The following daily entries have been submitted by Clive Minton and Susan Taylor, Australian researchers who are part of the Delaware Bay Shorebird research team. These entries were intended as file notes for reference purposes.
Delaware Bay Shorebird Migration - Daily Logs 2005
Our biologists and other members of the research team felt sharing these notes with the public via the Internet would be appreciated by the many folks interested in, and concerned about, migrating shorebirds. We hope to have daily log entries for the entire Shorebird research season which normally lasts through early June.
The entries are presented in their original, unedited form.
For more information on Delaware Bay shorebirds, see the Shorebird Information page.
DELAWARE BAY, NEW JERSEY, 2005 - DAILY LOGS
Well, the research team went home but the shorebirds didn’t! Whilst the international team set off in all directions on Saturday 4th June, and whilst all the equipment in the Reed’s Beach house was dismantled and taken back to the New Jersey Fish & Wildlife Department at Tuckahoe and near Trenton, the shorebirds did not depart on the evenings of the 3rd and 4th but remained on the bay.
In fact, they were joined by new arrivals. When chief scanner Ron Porter went out on Sunday 5th June he found lots of birds still on the beaches, with many of the Red Knot carrying engraved flags which had not previously been sighted this season. Furthermore there was an unduly high proportion of Red Knot carrying engraved red flags from Chile and engraved and plain orange flags from Argentina. This suggests that the new arrivals were a cohort of birds that had spent the non-breeding season in the southernmost part of the range, Tierra del Fuego.
The unusually large number of birds remaining in the bay in early June was confirmed by the Kathy Clark / Jim Dowdell / Ron Porter aerial survey on Tuesday 7th June. They located nearly 3000 Red Knot, a similar number of Sanderling, and nearly 8000 Ruddy Turnstone. The Ruddy Turnstone were split almost equally between the Delaware & New Jersey shores of the bay, but in the other species the greater proportion was in New Jersey.
Larry Niles decided, on the basis of the above information, that it was necessary to make a further catch of Red Knot in order to ascertain the weight profile of this late staying population. After considerable effort, on Thursday 8th June a catch of 46 Red Knot and 32 Sanderling was made on the shore at Fortescue. The weights were revealing. There were two clear cohorts in the Red Knot population. One group averaged about 180g, close to but at the bottom end of the take-off weight range. The other group averaged only 140g and was clearly composed of birds which had been on the bay for a short period. The retraps also confirmed the scanners’ impression that there was an exceptionally high proportion of South American flagged birds. Of the nine retraps, two had been banded in Chile and three in Argentina. Incidentally, eight of the 46 Red Knot were immature (one-year-old) birds.
The weights of the Sanderling were more uniform and averaged 83 g, close to the average take-off weight and an indication that most of the remaining birds were close to departure for the Arctic. Observations over the next few days showed decreasing numbers of all three species, and most had departed by the 14th June.
There is now considerable discussion and speculation about the interpretation of this year’s results and in particular of the continuation of arrivals of new birds until so late in the season – to well after the normal last major departure date from Delaware Bay in most years. One possible explanation is that some birds from non-breeding areas in southern South America are no longer making a direct flight from Brazil to Delaware Bay but are instead working their way up the south-east coast of the USA. In support of this was the sighting of 3000 Red Knot still in Virginia on June 1st, at two locations.
Analysis of the large amount of data collected in the field over the past 5 weeks may throw more light on the explanation. The principal task of all the scientists involved is now to analyse and interpret the data collected this year on:
A) Arrival weights, rates of weight gain, departure weights, weight profiles of different catches, departure datesAll the above data, and more, is being collected to help fully understand the situation occurring on Delaware Bay during the May/June stopover period for northward migrating shorebirds. Only with such comprehensive knowledge can problems be identified and explained and appropriate conservation actions planned and implemented. The knowledge is fundamental to the current move to have the rufa subspecies of the Red Knot placed on the “endangered” list.
So for the next few months, deskwork takes priority. The next planned fieldwork is monitoring, primarily by volunteers, of the numbers of Red Knot (especially juveniles) occurring on the eastern seaboard during southward migration in August-October. Then the next critical data will come from the aerial counts of Red Knot in the non-breeding areas of southern Argentina and Chile. These take place in late January / early February 2006. Unfortunately, no funding was available for a visit this year in late June / early July to the breeding grounds of the Red Knot in Arctic Canada to measure the number of nesting pairs on the study area which has been monitored for the last four years.
Saturday, June 4, 2005
Sure enough there are plenty of birds still on the beaches between Sunray and Norburys. Somewhat to our surprise there are still hundreds of turnstone and more than 100 red knot. This is the first time this season that those species have been present in such numbers on these southern New Jersey bay shores. Clearly the weather conditions on Friday evening prevented any further migratory departures.
But the Sanderling which were present - perhaps a couple of hundred - were mixed in with a very much larger number of semipalmated sandpipers. We tried to concentrate the sanderling in the single net we had set near Sunray Beach but it was difficult to get the desired sample of 50 sanderling into the catching area. Those that were present insisted on feeding right in the tide edge, running up and down between the quite significant waves in typical sanderling fashion. We also found that we had set the net slightly too far up the beach. When high tide had arrived we decided that the only option was to take a chance that the net would go out far enough to catch the sanderling. It didn't! The catch was 11 turnstone and just one sanderling.
Interestingly the turnstones had a much higher average weight than the sample caught at Reeds Beach the previous day. Nine of the 11 would have probably departed on the previous evening if the weather had been suitable. Time precluded a further attempt at catching as six team members had various flights to catch at Philadelphia airport in the afternoon.
A fascinating observation was made just after dawn on Reed's Beach. As usual, many thousands of laughing gulls arrived from their Atlantic coast night time roosting grounds to feast on the horseshoe crab eggs deposited on the beach by the night time tide. But they were almost totally absent from the 400 ft of shoreline where the gull exclosure, dismantled the previous day, had been. They clearly remembered that this was a "no go" area, presumably from a previous encounter with the unseen nylon monofilament lines. Unfortunately the ending of the fieldwork and dispersal of the team meant that observations were not continued to see how long it took the gulls to learn that this section of the beach was available, unimpeded to them again.
So how did the 2005 season pan out? Well, better than at one time seemed possible. Every year of the nine northward migration seasons now studies at Delaware Bay has been markedly different. With so many possible variables, this may not be surprising. The main features of 2005 are detailed below.
All three study species - red knot, turnstone and sanderling - were extremely late arriving on Delaware Bay from their non-breeding areas further south. Their arrival weights were also low. There was very little crab spawning until the end of the third week of May, due to the unusually cold sea temperatures, and many birds therefore only gained weight slowly. The saviour as far as the red knot were concerned was the almost enclosed Mispillion Harbor on the Delaware side of the bay which was awash with horseshoe crab eggs for a critical period of about a week. Gradually horseshoe crab spawning improved on the New Jersey shores of the bay, which were sheltered from three separate stormy days, and red knot subsequently transferred to that side of the bay for their final fattening process.
By the end of May the majority of birds of all three species had reached satisfactory take-off weights. They had clearly decided that this was the primary objective, and was achievable given the continuing supply of eggs, rather than departing northwards at their preferred date. Thus birds departed this year on average about five days later than normal. In 2004, and in a number of previous years, departures mainly took place between May 25th and May 28th, with few birds remaining after May 31st. In 2005 departures did not really commence in earnest until May 31st and there were still many hundreds of birds left, of all three species, when the main fieldwork ceased on June 4th.
A pleasing feature of the results this year was that red knot and turnstone populations recorded by the aerial surveys of the bay did not show any decrease from the previous year. Sanderling numbers were higher than in 2004, returning to levels typical of more recent years. Horseshoe crab spawning was lower than in 2004, but above the disastrously low level of 2003.
The closing of beaches most frequented by feeding shorebirds appears to have been a great success. The largest concentrations of shorebirds were frequently found in these areas and were able to feed free from significant levels of human-induced disturbance. The gull exclosure experiment also potentially leads to a means of increasing the availability of horseshoe crab eggs to shorebirds, and it will be continued next year.
Let us hope that the apparent early snowmelt on the arctic breeding grounds gives the birds the opportunity to breed more successfully in 2005 after two disastrous breeding years in 2003 and 2004.
We hope that you have enjoyed these daily log reports, sharing the highs and lows of this season of shorebird northward migration through Delaware Bay. These vagaries are typical of fieldwork studying wildlife. We hope to continue the story next year.
Friday, June 3, 2005
The many thousands of laughing gulls present on the beach proved a real problem. They occupied almost every inch of space, and had pushed the shorebirds up to the top of the beach and were largely preventing them from feeding. The gulls themselves were having a feeding frenzy as, for the first time this season, there was a scum of horseshoe crab eggs on the tide edge which were being washed up and deposited on the beach at the high-tide mark. Repeated jiggling cleared the gulls from the catching area only temporarily, and this process was repeated perhaps as many as 25 times over the half-hour period which it took Nick to move the shorebirds along the beach towards the catching area. Just as we were contemplating a catch of 50-100 knot and turnstone mixed with an undesirable 200 laughing gulls, a miracle happened! Some unseen cause made the gulls temporarily lift-off from the whole beach making room for more shorebirds to walk quickly into the catching area. The net was immediately fired and produced a nice catch of 42 red knot and 106 turnstone - and only ten laughing gulls.
We now know why so many shorebirds are still here - on the 3rd June. A significant proportion of birds of both species were well below the normal range of departure weights, some even being at almost 'fat free' or arrival weights (e.g turnstone at 100 gm and red knot at 109 gm). These medium and, especially, low-weight birds will now find it difficult, if not impossible, to get to the breeding grounds. Some of these are probably young birds making their first northward migration (at age 2). Support for such an explanation is that the re-trap rates were much lower than normal (5-7% compared with the normal 15-20%). Young birds will not have previously been exposed to banding activities on Delaware Bay. It is also possible that some birds were at low weight because of problems they have encountered at an earlier stage of this year's northwards migration. Others may have found food just too hard to obtain during their stay here. But it is more likely that most were recent arrivals, younger birds being known to migrate later than experienced adults. Seven of the red knot were actually one-year old birds in non-breeding plumage and these are unlikely to be travelling back to the breeding grounds in any case.
There were so many gulls on the beach this morning that huge numbers penetrated into the 'gull exclosure' area. However, numbers were much thinner there than on the rest of the beach, and there were noticeably more uneaten eggs on the tide edge and on the beach under the exclosure than elsewhere. Furthermore, when we first came down onto the beach, there were 150 shorebirds feeding in the exclosure, and these remained when the more nervous gulls flew off.
During the early afternoon, a meeting of the full team was held. Larry Niles briefed everyone on the outcome of the meeting in Washington. He outlined the steps and timescale for preparing a "status report" as the first formal stage for an emergency listing of the rufa subspecies of the red knot as endangered.
Later in the day, the gull exclosure was dismantled, and the materials prepared for storage until next year. Whilst the trial was not fully successful, it certainly shows promise and tangible benefits in keeping many gulls off the beach, allowing some shorebirds in, and preserving many horseshoe crab eggs from gull predation. It is intended to continue the trials next year, including replicating the exclosure at a number of other locations on the shores of the bay, especially where large concentrations of feeding shorebirds regularly occur.
Taking down the exclosure was not quite as easy as envisaged! This was primarily because Clive forgot to consider the tide height. Half the exclosure was already full of water when we started and completely full of water by the time we finished. All four of us were wading around fully clothed in waist deep water. And we still needed to use the step-ladder to undo items at the top of ten foot poles. A step-ladder looks pretty funny when it is out in the sea with only the top three steps above water level! And the person on it looks even funnier. Also, it wasn't easy walking around in bare feet in the sea which was full of mating and spawning horseshoe crabs. Cold pouring rain at times didn't add to the fun. Furthermore, as usual, the rain got into the telephone system and put us off-line for 24 hours - hence the late appearance of this batch of daily logs.
The day ended with a wonderful seafood barbecue and chowder (prepared by Chris Porter). Team leader Larry Niles thanked everyone for their efforts in making this year another successful fieldwork season. The team disperses (migrates!) tomorrow.
Thursday, June 2, 2005
It was good that the birds had ‘got away’, as the weather gradually deteriorated during the day, with increasing cloud, easterly winds, and some rain starting during the night. Such weather conditions are not suitable for inducing or successfully completing migration.
The meetings in Washington were productive – a second meeting being added to enable a senior officer of the US Fish and Wildlife Service to be briefed about the red knot situation. There is now a strong move for the rufa sub-species of red knot to receive an emergency listing as an endangered species.
Wednesday, June 1, 2005
At most locations it was immediately apparent that there were significantly fewer birds on the beaches today than yesterday, especially red knot and sanderling. Red knot at Reeds Beach, for example, had reduced from their peak of 4,000 only two days previously to just under 1,000. Overall, the aerial survey showed that the number of red knot on the bay had fallen to 8,605 from 15,345 eight days previously. Sanderling numbers had almost halved, from 12,765 to 6,675. However, ruddy turnstone numbers had remained almost constant: 42,190 compared with 42,995. As usual, huge numbers of semipalmated sandpipers was counted on the bay shores (58,360); and there will have been many more that were not countable because they were feeding or roosting on the extensive saltmarshes and brackish lagoons behind the shoreline when counting took place.
Humphrey and Nicholas carried out the last of the aerial radio-tracking surveys around the bay at low tide. They found 15 red knot carrying radio transmitters, 12 in New Jersey and three in Delaware. This compares with the count of 28 on the low-tide aerial survey two days previously, and is consistent with the reductions in the red knot population shown by the aerial counts and the beach surveys.
Significant horseshoe crab spawning was observed, not just by field-workers on the beaches but also from the planes. The weather remained calm, and reasonably warm, although the cloud did increase as the easterly wind freshened to some extent later in the day.
In the afternoon, six members of the team, led by Larry Niles, departed by road for Washington. The purpose of the visit was to make requested presentations on the red knot ‘population crisis’ to the staff of a number of Senators and Representatives from New Jersey and other relevant areas.
The ‘scanning team’, however, remained at Delaware Bay in order to continue collecting as many sightings as possible of engraved flags before the birds leave on migration.
Tuesday, May 31, 2005
The radio tracking also indicated that not many red knots had departed. A visit at 3a.m.to Stone Harbor by Humphrey located 20 red knot with transmitters at the night-time high tide roost. This is only a small reduction from the 24, which were found the previous night.
The weather continued fine with only a light NW wind. A moderate level of crab spawning was observed on the afternoon tide; and the ‘pot holes’ on the beach and upturned crabs indicated that the night-time tide also had produced further crab spawning.
A nice catch of 76 red knot and 51 ruddy turnstone was made on Reeds Beach in the morning. Amazingly, four of the red knot carried bands put on in Argentina, and one of the ruddy turnstone had been banded in northern Brazil one month previously. Average weights for both species reached the highest levels for this year, at 185 gm for red knot and 150 gm for ruddy turnstone. More than 90% of the population seemed to have satisfactory weights, and there was only a small ‘tail’ of moderately low-weight birds. Overall, the majority of birds now seem to be at or very close to take-off weight, and it is slightly surprising that more have not already left. In many of the earlier years of the study, the beaches were almost bare of birds by May 31st, with peak departures occurring in the period 25th-28th May.
The origin of re-traps (i.e. birds already carrying a band when caught) is always of particular interest. This is especially so for birds caught twice in the same migration season when changes of weight can be measured during the stopover period at Delaware Bay. One of the red knot re-captured today had been originally banded on 17th May at Fortescue (just 20 miles further up the New Jersey shore of the bay). Then it had weighed 101 gm; today it weighed 185 gm. The increase of 84 gm in 14 days (6 gm per day) is a rate of weight gain in relation to its ‘fat-free’ weight of close to 6% a day. This is typical of what birds need to achieve in order to gain the pre-migratory weight required in the time available. Interestingly, this bird also carried a radio transmitter, so when the automatic receiving stations are down-loaded and analysed, we should know in detail how it has spent the last two weeks on Delaware Bay.
A re-trapped turnstone had similarly shown the requisite increase in weight, from 80 gm on 14th May to 164 gm today. This 84 gm increase in 17 days (on average 5 gm per day) is also equivalent to a 6% per day weight gain.
Extensive scanning continued of knot, turnstone and sanderling. Lots of ‘new’ birds are being seen each day as the flocks are systematically scanned. However, it may also be that there are continuing small arrivals of additional birds from further south.
The day ended with two notable events. Ron Porter saw a total of 4,100 red knots departing from Stone Harbor area just before dusk, in flock sizes ranging between 20 and 600. This seems to be the first big departure for this season, at the amazingly late date of May 31st. Secondly, most of the team were treated to a wonderful show of slides and digital photos of shorebirds in North America by world-renowned photographer Kevin Carlson (who lives at Reeds Beach).
Monday, May 30, 2005
So, just as early in the expedition we eagerly scanned the beaches first thing in the morning to see what birds had arrived, now we look to see whether numbers have decreased. We expected this morning to see a marked reduction in numbers, especially because Allan Baker and Patricia Gonzalez had observed some flocks of red knot leaving Reeds Beach in a northerly direction the previous evening.
But we were wrong! The first clue that birds were still remaining here for further fattening came from Humphrey’s 2 a.m. radio-tracking visit to the night-time red knot roost at Stone Harbor. Twenty-four birds with transmitters were located, only a small reduction on the number present the previous day. And early risers at the Reeds Beach house found large numbers of red knots and turnstones on the nearby beaches feeding vigorously. A careful count during the morning gave a figure of 3,800 red knot and at least 1,050 ruddy turnstones. This is the largest congregation of red knot on Reeds Beach for several years – and what a wonderful and memorable sight for everyone!
The scanners naturally had a field day, and over 300 individual red knot with inscribed leg flags were recorded. About 50 turnstone were also seen, but only a small number of sanderling as these have now transferred to the less-watched and scanned beaches further south.
Because the banding team’s target was again sanderling, they also went south at midday and set a net on Sunray beach, about a mile south of Norbury’s landing. It did not take long for a satisfactory flock to gather in front of the net, and a good catch of 100 new birds and 10 re-traps was made. The weights of these birds were extremely satisfactory, with an average weight of 86 gm, being close to the maximum average ever recorded for this species (90 gm). Some individuals weighed over 100 gm with a peak of 104 gm. There was only a small ‘tail’ to the distribution, indicating that almost all birds are on target to reach satisfactory departure weights. A bird at 45 gm appeared to be going nowhere, however.
Time was taken during the morning to further modify (Mark 10) the gull ‘exclosure’ on Reeds Beach. Observations since the previous modification indicated that it was now quite effective at keeping out the laughing gulls, but that only occasional sorties of up to 200 red knot at a time were using it to feed or roost. Four of the seven poles at each end of the structure and in the centre of the exclosure were removed in order to create a greater impression of ‘openness’. The suggestion was that the poles may previously have appeared too great a physical barrier, inhibiting some birds from entering the area. So the total 600ft x 60ft exclosure is now using only nine poles to hold up the network of nylon filament wires. Hopefully, this will encourage more red knot to utilise the increasingly rich food resources in the area.
The weather remained calm and sunny all day, and temperatures were higher than at any time in the preceding month, though only about 77° F (25° C). Some crab spawning was apparent in the form of depressions in the sand and upturned crabs stranded on the beaches after the night-time tide. There were still some horseshoe crabs in the tide edge on the daytime high tide (3.40 p.m.), indicating a continuing modest level of spawning.
The final fieldwork of the day was a night-time radio tracking flight by Humphrey and Nicholas over the Atlantic marshes and the shores of Delaware Bay at low tide. The results were fascinating. Twenty-eight radio tagged birds were located, indicating that departures of red knot at dusk this evening were only on a small scale. All 28 birds carrying transmitters were in New Jersey. It was of particular interest that 14 of these were in the Atlantic marshes between Stone Harbor and Cape May Court House, and a further two were at Stone Harbor point itself. These observations indicate that, at low tide at night, a significant proportion of the red knot population was feeding in saltmarsh habitat – quite different from the beach habitat where they largely feed during the day. Although they are feeding on horseshoe crab eggs during the day, they are (at least this year when mussel spat is plentiful in the marshes) topping up at night on alternative food. Twelve birds were also located within Delaware Bay, but nine of these were at Egg Island near Fortescue, a well-established alternative night-time roost (and possibly feeding?) location.
What will tomorrow bring?
Sunday, May 29, 2005
Looking out from the balcony of the Reeds Beach house at first light confirmed the impression that few birds had departed (as also did visits to a range of beaches during the morning). Red knots were still present in the flock on Reeds Beach, with numbers increasing for a time to 3,000. There were also plenty of turnstones on the beaches; and further south, near Norbury’s Landing and Villas, there were many sanderling. Although some departures had taken place, they must have been on relatively small scale. This indicates that most birds had not yet reached the optimum weight for migration.
It was a lovely fine morning and remained calm and sunny all day. An attempt was made to catch sanderling, as three days had elapsed since the previous catch. It is highly desirable to monitor the weights closely at departure time to see what departure weights are achieved, and what proportion of the population reaches a satisfactory departure weight by the necessary date (roughly 26 May - 1 June). We set a net at Kimball’s beach, but were not successful, partly on account of the complex geography of the shoreline there – a major creek, some sandy islands and some small pools; this made it difficult to get the sanderling into the catching area.
On the afternoon high tide, Humphrey and Nicholas carried out another radio-tracking survey of Stone Harbor and the whole of the shoreline of Delaware Bay. They located 28 red knot, all in New Jersey. They got off the plane in Delaware where they were met by members of the Delaware team and driven to their base.
Most of the rest of the team caught the 2.30 p.m. ferry to Delaware for the annual get-together with our counterparts on that side of the bay. This proved a most fruitful liaison opportunity for everybody. Our joint results have shown even more this year that the shores of Delaware Bay are considered by migrant waders as a single food resource and stop-over site. This makes it even more imperative that there is close collaboration and liaison between the diverse teams based in New Jersey and Delaware. The Delaware team were most generous hosts, and everyone felt it was perhaps the most productive and enjoyable of our get-togethers. The three-hour drive home afterwards was no problem after such a pleasant evening.
Saturday, May 28, 2005
Needing a catch of red knot, turnstone and sanderling today/tomorrow, Larry Niles decided that we should try to get an initial catch today on Reeds Beach, because there have been so many red knot present there over the last few days. Only one net was set and after a gentle twinkle by Mark Peck and Nicholas Branson a very satisfactory dry catch was made of 81 red knot, 52 turnstone and 9 sanderling. The weights of these birds were again close to the average for the last nine years for this date and slightly above the weights recorded two days ago. It seems that the majority of birds are currently on track to achieve a satisfactory weight provided that feeding conditions remain good over the next few days. However, there is still a small “tail” to the weight histograms of the red knot and turnstone, with about 10% of the birds lagging well behind the main population in their weight gains. Interestingly, one sanderling was aged as a juvenile (i.e. one-year-old); it was in partial breeding plumage and not very heavy.
There were, again, very good numbers of red knot all along Reeds Beach and on many of the beaches south of there right down to Villas. With numbers of at least 2000 at Reeds Beach again these observations further suggest that no major departures of red knot occurred last night. Good numbers of turnstone were also still present at all locations and, at most, only a modest departure of this species could have occurred.
With red knot continuing to be present on the more accessible beaches, the scanners had another field day. Over 250 red knot with inscribed flags were again recorded, plus 60 turnstone and 40 sanderling.
It appeared to be quite a good day for spawning horseshoe crabs again, on both the night-time and day-time high-tides. This naturally attracted large numbers of laughing gulls all over the beaches soon after dawn and again on the beaches around the 2.00 p.m. high-tide. However, crab spawning in the Fortescue area was small.
The gull exclosure was keeping out the majority of the laughing gulls though small sorties of up to 100 occasionally walked in. Similar numbers of red knots also went into the area to feed but did not stay long. Flocks of hundreds of red knots were frequently present right up to the ends of the exclosure but most were reluctant to enter. It is almost as if a brick wall is present!
The horseshoe crabs responded dramatically to the calm sea and warmer temperatures and, having been unable to spawn for the last two or three days, the pent-up demand was released. At the lunch-time high tide on Reeds Beach spawning crabs were a metre o so wide all the way along the beach. However, it was still noticeable that there was a great surfeit of males – perhaps five males to one female – and so the appearance probably gave an exaggerated impression of the number of eggs laid. Nevertheless, it was the first really satisfactory spawning of the season and couldn’t be more timely, given that the birds need to have all departed for the final leg of their northward migration to the Arctic over the next few days. Heavy crab spawning was also reported, by a number of other members of the team, at various locations on the New Jersey side of the bay.
Another heart-warming sight was the large congregation of red knot feeding and roosting on Reeds Beach for much of the day at both low and high tide. Numbers at times were estimated at up to 2000, the largest flock or red knot seen on this beach for two or three years. Knot flocks were again widely spread on the New Jersey shores of the bay, with good numbers also at Cooks and Kimbles.
Humphrey Sitters and Nicholas Branson’s aerial radio-receiver survey of the bay produced similar results to yesterday, though today’s survey was carried out at high tide rather than low tide. Thirty-one red knot carrying transmitters were located, all but one on the New Jersey side of the bay. One of these birds was a “new” one; meaning that 45 out of the 50 birds carrying radio-transmitters have now been picked up by the hand-held, radio-tracking receiver during the last 48 hours.
With so many red knot on the more accessible beaches in New Jersey, the scanners had a field day. 260 different red knot carrying individually inscribed leg-flags, put on this year and in the previous two years, were located. Additionally, over 200 ruddy turnstone flags were identified and about 20 sanderling. At the present rate of making flag sightings we seem to be on track for generating a sufficient amount of data to calculate survival rates for all three species over the last year.
Further improvements were made to the gull exclosure on Reeds Beach early in the morning and observations on the effect of these were made at regular intervals throughout the day. The “roof” of the exclosure is now composed of parallel lines of nylon monofilament line 400 feet long and spaced only one and a half feet apart (with a total width of the exclosure of 40 feet). This makes it much more difficult for gulls to fly into the exclosure area from above and makes it more likely that they will be impeded when they try and fly out of it, having originally entered it by walking from the ends or swimming in from the sea. The results were encouraging. Throughout the day there were far greater densities of gulls immediately outside each end of the exclosure than inside the exclosure. Often, there would be 500 or more laughing gulls and a small number of herring gulls within 100 feet of each end. But a maximum of only 100 laughing gulls at a time were recorded within the exclosure and most of the time there were fewer than this. Red knot, in numbers up to 150 at a time, were seen penetrating into the exclosure area by walking in from both ends. They clearly benefited from the extra rich feeding there. However, the main flocks of red knot (and turnstones) remained outside, but right up to the ends of the exclosure – sometimes in gatherings of 500 up to 1000 or more at both ends. We will continue with observations for a further day or so before deciding whether any further modifications to the exclosure are necessary, or possible.
The final fieldwork for the day was another visit to Stone Harbor by Humphrey Sitters with a hand-held radio-transmitter receiver to see which red knot came to roost tonight at the Stone Harbor night-time gathering. Thirty different radio-tagged individuals were recorded. This is a similar level to preceding evenings and suggests that there was no major departure migration of red knot at dusk this evening.
Thursday, May 26, 2005
The main activity of the core team was scheduled to be catching waders, as no samples of sanderling, turnstone or ‘bay’ Knot had been obtained for four days. But before the shorebird catching was attempted, a catch of 120 Laughing Gulls was made in a single net at Reeds Beach at the request of the team from South Georgia who are studying avian-borne diseases by taking cloacal swabs.
After this exercise was quickly completed, both nets were set along Reeds Beach. and after a gentle twinkle an excellent catch of all three target species was made: 138 red knot, 96 turnstone, 60 sanderling. With a strong team, augmented by a range of local helpers as well as three volunteers who had driven over from Baltimore, Maryland, that morning (leaving at 2.15 a.m.!) all birds were fully-processed and fitted with engraved leg flags. One of the red knot captured had originally been banded on Southampton Island in the Canadian arctic on its nest on 28th June 2002 and re-trapped, again on its nest, on 27th June 2003 (this would mean that it was a male, as only males return each year to the breeding territory). Also in today’s catch, but from the other end of the 10,000 mile migratory path, were two red knot which had been originally banded in Argentina.
It is very pleasing to report that, on all three species, the mean weights were close to the averages for this date for the whole nine years of this study. This means that after a very slow start, with late arrivals and low arrival weights, birds have steadily been finding sufficient food gradually to catch up and to be almost on track for achieving departure weights by the required date. In the case of the red knot, it seems that this has been achieved by intense gorging on the horseshoe crab eggs which were abundant for over a week in Mispillion Harbor. With the population size now so reduced, it seems that this one major source of food can alone make a significant contribution to the food needs of the whole population. Then, in the last two-three days, with Mispillion ‘eaten out’, the red knot have moved across the bay to the New Jersey shores where cumulative modest levels of horseshoe crab spawning are now giving a reasonable supply of eggs on the beaches. The high winds of the last two days have also contributed by uncovering some previously buried crab eggs.
This mass transfer of the red knot population to the New Jersey side of the bay, and the strong favouring of Stone Harbor as a night-time roosting location, are beautifully illustrated by recent results from the radio transmitter work. Using a hand-held receiver station, Humphrey Sitters has been recording the presence (or absence) of birds carrying radio transmitters. Fifty red knot have had radio transmitters placed on them this season. On Wednesday night 28 of these birds were present at the Stone Harbor roost at dusk. Tonight, 26 were present at dusk at 8.30 p.m., but this number had increased to 33 by high tide at 11 p.m. During the day, an aerial survey of the bay at low tide located 30 red knot with transmitters. 28 of these were on the New Jersey shores of Delaware Bay, one was at Stone Harbor, and only one was on the Delaware shores of the bay. Altogether, during the two evening surveys and the day survey, 44 different red knot carrying radio transmitters have been located. Out of the total of 50 carrying transmitters. This inter alia confirms other evidence that negligible northward departures on migration have taken place so far this month.
Given the forecast for improved weather, and the relatively high weights of the samples of birds caught today, we would expect the first really significant migratory departures to occur on Friday and Saturday evenings.
It was fortunate that the majority of the day had been scheduled for a meeting at the Reeds Beach house with a range of parties involved in wildlife conservation; the purpose of the meeting was to discuss the possible listing of the red knot as an endangered species.
The “scanners” did continue, however, with their activities for part of the day, even in the bad weather conditions, but reported many fewer red knot and other shorebirds than on the previous day. Monday 23rd May still stands as the best result so far, with 193 different engraved flagged birds located (88 ruddy turnstone, 74 red knot and 31 sanderling).
Further minor modifications were made to the gull exclosure. It does seem to be keeping most of the Laughing Gulls off that section of the beach for large parts of the day. It is also still keeping out many of the shorebirds. But red knot seem to be the most prepared of the three shore-feeding species to enter the area, and on several occasions flocks of over 100 were feeding or roosting, unmolested by Laughing Gulls, in the exclosure area.
An evening visit to Stone Harbor again found a large collection of red knot just before dusk, estimated at 14,000. For the second consecutive night, no migratory departures were observed, but this is not surprising considering the appalling weather conditions and strong head winds they would have faced.
A visit to Stone Harbor from 7 p.m. until darkness fell at 8.30 p.m. revealed a vast gathering of red knot, estimated at 20,000. This must mean that all the red knot from the Delaware and New Jersey sides of the bay had collected there, together with the 500-1,000 red knot which feed in the saltmarshes around Stone Harbor. It was particularly interesting that, at 8.01 p.m., a small flock of 95 red knot lifted off from the gathering and headed northwards, eventually climbing and forming into a V-formation. This is probably the first northwards migratory departure of red knot this season, after their stop-over in Delaware Bay.
A further modification to the gull exclosure was made in the early evening.
Monday concluded with a lobster bisque supper made by Ron and Chris Porter to say farewell to team member Ruth Croger who was due to return to England the next day.
Now for Tuesday, 24th May.
This was a critical day in this year’s studies. The weekly aerial count of the bay shores and Stone Harbor was expected to coincide with the peak numbers of red knot, Ruddy turnstone and sanderling. The results confirm that there had been major new arrivals of all three species since the previous aerial survey on 18th May. Red knot had increased from 4,480 to 15,345. This is fairly close to last year’s peak figure of 13,315 (on 25th May). There had been a big transfer of red knot from the Delaware shores to the New Jersey shores of the bay, with 9,900 found on the latter; the big storm of 20th May seems to have somewhat disrupted their food supplies on the Delaware beaches because the strong winds were directly on-shore.
Turnstone numbers were 42,995 compared with 15,445 only six days earlier. As usual, there were rather more on the Delaware shores (23,775) than the New Jersey shores (19,220). The total is close to the 25th May count in 2004 (45,380).
Sanderling numbers had increased from 8,240 to 12,765. This is well above the unusually low aerial survey count of 7,105 on 18th May 2004. As usual, there were more sanderling in New Jersey (7,765), but the 5,000 counted in Delaware is a particularly good total there for this species.
A complete count from the ground and from boats was made of all the beach shores on the New Jersey side of the bay. Unfortunately, an increasingly strong on-shore wind prevented any boat counts on the Delaware side, but ground counts were carried out at the main accessible locations. A comparison between the ground and aerial counts is currently being prepared.
Overall, the count figures, coupled with the catch weight data and visual observations, suggest that this year’s count may well be close to the total number of individuals of each species visiting the Delaware Bay stop-over in 2005. Few birds could yet have departed northwards, and the great majority of birds coming here should have arrived by 24th May.
Observations of the beaches during the counts indicated some further Horseshoe Crab spawning on the New Jersey bay shores, but significantly less than on the previous two days. However, nowhere were Horseshoe Crab eggs present on the surface of beaches in visible patches as they have been at some stage in each of the previous eight years of the study. During the day, the weather became increasingly cold and cloudy, and the wind freshened considerably from the NE, ahead of the major deterioration forecast.
Early in the morning, before the wader-counting activities took place, a further catch of 56 red knot was made at Stone Harbor, after a brilliant combined twinkling effort by Humphrey Sitters, Mark Peck and Nicholas Branson. The mean weight was almost identical to the previous day, but the spread was greater. Whilst there were a number of birds weighing between 190-197 gm, there were some newly-arrived birds weighing only 97, 99 and 100 gm. These birds will have a lot of hard eating to do if they are to double their weights in the next week – as May 31st is close to the last day for take-off to meet the optimum arrival time on their Arctic breeding grounds.
A further visit to Stone Harbor in the evening again revealed a large night-time roost gathering of red knot, estimated at 15,000. However, this may be a conservative figure as radio tracking observations indicated quite a few new birds arriving just after dark – probably these last cohorts were coming from feeding areas on the Delaware side of the bay. It was later learned that the high-tide roosting location sometimes used at night by red knot behind Mispillion Harbor in Delaware is currently deeply flooded. This may be the reason why it appears that the whole of both the Delaware and New Jersey populations of red knot are roosting together this year on the sandbanks at Stone Harbor. Even these were largely submerged by the extremely high evening tide – the highest forecast for the month, but with its height accentuated by low pressure (1005 mb) and by the now strong on-shore NE wind.
It was another 5.00am rise and 5.30am departure – becoming the norm for the banding team and for the scanners. This time the target for the banding team was a sample from the 1000 or so red knot which are feeding in the marshes around Stone Harbor and roosting on Stone Harbor point, on the morning, daylight, high-tide. The beaches are extremely flat, making the position of the high-tide line, and consequently the birds’ roosting place, difficult to predict. After much debate two nets were set and fortunately the tide just came to the edge of the catching area of one of these and, after some excellent twinkling, a catch of 84 red knots was made.
It was immediately apparent that many of the birds we were handling were extremely fat. This confirmed observations of red knot at this location made the previous day by the scanners. The average weight of the sample was 166gms and several individuals weighed over 180gms (up to a maximum of 196gms). This compares with the fat-free weight of around 110gms and an arrival weight of some individuals down to 90gms. Also of interest was the capture of four first-year birds (ie birds hatched in the arctic in summer 2004), all of them in complete non-breeding plumage. Each year a few of these young birds come as far north as Delaware Bay, but they do not continue to the arctic as red knots do not breed for the first time until they are two or three years old.
This cohort of relatively high-weight birds that we caught on the Atlantic coast at Stone Harbor today is clearly quite different from the low-weight population sampled yesterday at Fortescue. The weights also do not correspond with the “medium” level of weights of the 93 red knot caught by the Delaware team in Mispillion Harbor on Saturday. Discussion is continuing on the likely provenance of these birds; the re-capture of two birds previously banded in Georgia may be significant.
Scanners on the New Jersey side of the bay reported some hundreds of red knot at several different locations on the bay shores – Fortescue, Moores Beach, Reeds Beach, Kimbles and Rutgers. This is the first time this year that this has occurred. Better numbers of horseshoe crabs were also seen spawning at most of these locations.
The gull exclosure on Reeds Beach was again full of gulls. But this time, quite a few red knot were also feeding in the area and there was even a small roosting flock.
A little more crab spawning was observed, but still only at a modest level, and far less than would normally be expected only a day before the May full moon.
Early morning observation of the gull exclosure on north Reeds Beach again showed it crammed full of laughing gulls, but encouragingly, some turnstone also. We have some ideas for further modifications, but no time to implement them!
It is now five days since we made any catch of shorebirds. Our regular monitoring of arrival weights and rates of weight gain after arrival is prejudiced if we can’t maintain this – preferably with catches of samples of around 50 of each of the three main study species at three or four day intervals.
Today perseverance at last paid off, aided by the fortunate timing of the arrival of some small groups of red knot for the second of our two catches, on the shore at Fortescue. All 40 red knot on the shore were caught, together with a total (in the two catches combined) of 102 sanderling and 33 turnstone. As in all previous catches this season the average weight of the birds caught was at the bottom end of the range for the eight previous years for this particular date. Weights of some individuals had increased, but there were other birds of extremely low weight which had obviously only just arrived.
It was a great relief to the team to finally achieve what is only its second catch of red knot for the 2005 season – on the 22nd May! But this was eclipsed by the sighting of no less than 13,000 knot at the high-tide roost in Stone Harbor at around 8pm. It is well established that most of the New Jersey red knot population adjourn to Stone Harbor at night, and that some birds from Mispillion Harbor from the Delaware side of the Bay come there too. But this gathering tonight would appear to be the whole of the red knot population from both shores of Delaware Bay plus those that are currently feeding in the marshes around Stone Harbor itself. A truly amazing sight, magnified by the previous dearth of red knot almost everywhere except Mispillion Harbor so far this season.
Fittingly, the day ended with a celebratory “shrimp on the barbie” get-together of all the various shorebird researchers based on the New Jersey side of the bay.
The banding team continued with its plan for Friday and took the equipment out by boat from Stimpsons Islands to try and catch red knot on the marshy shores east of Moores Beach. This proved extremely difficult with the birds having a great many different pieces of shoreline to land on and with accessibility difficult, even by boat, because of the shallow water. After a 5.30am start, and four hours of perseverance, including setting the net in two different locations, we gave up.
One of the scanners reported 400 red knot on the shores of Fortescue so the banding team made haste to get there. But by the time we arrived and set the net there were fewer than 50 red knot, and this, coupled with the large number of laughing gulls, again made it impossible to get an adequately-sized sample of red knot into the catching area in front of the cannon-net. So it was a thoroughly unsuccessful day for the banders. As so often when trying to catch red knot it was a question of being at the right place at the wrong time and vice versa. We seem to be perpetually a day, a few hours, or even just an hour behind the red knot!
The scanners found a few more knots on various New Jersey beaches to look at today but still had to be mainly content with finding and reading engraved leg-flags on ruddy turnstone and sanderling.
Little new crab spawning was seen, the horseshoe crabs appearing to still be discouraged after the cold and rough weather the previous day. Rather more crab eggs were available for the shorebirds (and gulls!) on some beaches because of the washing out of buried eggs caused by the previous day’s rough weather. But this slight increase in food supply was short-lived and appeared to have been consumed by the end of the day.
Not suprisingly, the majority of the team were confined to the Reeds Beach house most of the day. However, it was a great time for making engraved leg-flags and forming colour bands ready for future catches. Also for catching up on paperwor, e-mails and sleep.
A few brief sorties were made, but mostly revealed beaches full of laughing gulls and huddled clusters of shorebirds looking miserable. However, the rain did temporarily stop in the early evening and this produced the highlight of the day when 4500 red knot were found sitting out an extremely high-tide at dusk at Stone Harbor point. We watched these until it was too dark to see, in the hope they would give us a clue to where they might be mist-netted at dusk – on a calmer day of course. But like shorebirds everywhere around the world they moved off before the light had completely faded, probably going to Champagne Island or to some remote part of the saltmarshes where they would be potentially more free of ground predators approaching during the night-time.
The gull exclosure on Reeds Beach continued to attract very high numbers of laughing gulls!
No horseshoe crab spawning was apparent on any beach on either the morning or evening tide because of the cold, rough weather.
The lack of active fieldwork today provides an opportunity to include in this daily log the work of an eight- member team from the Virginia Tech. at Blacksburg, led by Prof. Jim Fraser and Dr Sarah Karpanty.
Their project aims to look at egg depletion by foraging birds (includes shorebirds and gulls) on the shores of Delaware Bay (both sides).
The study is trying to demonstrate that reproduction and survival of red knot are limited by processes in the Delaware Bay. In 2004, they conducted a radio-telemetry study of red knot and demonstrated that the distribution of red knot in Delaware Bay is most strongly influenced by the abundance of crab eggs. The distribution of red knots was also impacted on by the abundance of Donax variablis, and the levels of disturbance on bay beaches.
In 2005 they are studying whether foraging birds (shorebirds and gulls) are depleting available egg resources around the bay. If there is evidence that foraging birds are depleting available horseshoe crab egg resources, then they will have strong evidence that the red knot may be limited by the availability of this food resource. This data will be used to design the best management strategies for both shorebird and horseshoe crab populations.
To date, they are finding an extremely uneven distribution of surface eggs around the bay. They are finding that laughing gulls are depleting surface eggs within the first few hours after sunrise on all ten study beaches around the bay. Shorebirds arrive about one hour after the laughing gulls and after the majority of surface eggs have been eaten. They will continue to document arrival times of different foraging bird species and depletion patterns of eggs for the remaining few weeks of the season. To achieve this information they have to be out on the shore at 2.30am every morning so that they can measure available crab eggs on the beaches before the first laughing gulls arrive, as it gets light, around 5.15am.
Thursday, May 19, 2005
The boat trip indicated some significant crab spawning at some locations, including, for the first time, in the creek mouth at Moores Beach. However, crab spawning is still very patchy.
During the day the knot scanning team was transported by boat to the saltmarshes. In this location scanning is much more difficult than on normal beach shores but nevertheless they managed to read more than 12 engraved leg-flags as well as some cohort colour-combinations from previous years. Humphrey Sitters also moved one of the automatic radio-transmitter tracking stations to the East Moores Beach saltmarsh area.
The team also set out by boat to try and make a canon-net catch of red knot on the saltmarsh on the 6.30pm high tide. However, just before the boat reached the destination the scanners observed the red knot from along the coastline taking off groups and flying away high eastwards towards Stone Harbor. It is not quite clear why they departed for their night-time roost areas so early; probably yet another indication that their clam food supply was covered by the incoming tide and there was no other alternative available to make it worthwhile staying.
So the catching attempt was abandoned and most of the team rapidly adjoined to Stone Harbor. There, sure enough, was a sight to be seen. For the first time in New Jersey this season we were able to look at large congregations of knot. About 1800 were roosting over the high tide period on the beaches at Stone Harbor point and a similar number were roosting in several flocks in the saltmarsh vegetation on the adjacent Nummy Island. These flocks almost certainly contained the red knot that had been feeding earlier in the day on the New Jersey side of the bay but may also have included some birds from Delaware. Radio-tracking in 2004 showed that some red knot which spent the da feeding at Mispillion Harbor came over to Stone Harbor to roost at night (a round trip of about 40 miles).
During the day the gull exclosure on Reeds Beach was completely re-constructed. This was in an effort to create a structure that world more readily encourage access by shorebirds whilst having a significant deterrent effect on gulls. With previous designs shorebirds had only occasionally been seen feeding in the area in though food must be richer there than elsewhere because of its generally successfully exclosure of gulls. The height of the nylon monofilament "wires" was raised to eight feet and the number and distribution of poles supporting the wires were placed in three separate groups, well-apart to minimise any visual impact. Unfortunately, we overdid it! A few shorebirds did enter the area but massive quantities of laughing gulls – maybe as many as 2000 on the evening high-tide – clearly discovered the rich food resources there and were prepared to brave the occasional impact or near miss with an unseen nylon monofilament barrier. So, it will be back to the drawing board again. But it is beginning to look increasingly doubtful that we can construct an exclosure which will be acceptable to the shorebirds as a feeding area but at the same time will deter the majority of gulls (which take the majority horseshoe crab eggs currently available).
The weather yet again today was sunny and, in the morning, calm and yet warm. But in the late afternoon, as cloud increased from the west, a fresh easterly wind came up and it became distinctly chilly. Rain is forecast for tomorrow and may interfere with planned fieldwork.
Wednesday, May 18, 2005
The aerial survey recorded a total of only 4,480 red knot in Delaware Bay. However, the inner parts of Mispillion Harbor, in Delaware, are difficult to count from the aerial survey flight line and some red knots feeding there may have been missed. Of the total counted, 2520 were in New Jersey, with 2460 of these being in the Bidwells Creek to East Moores Beach section. The traditional red knot sites of Reeds Beach, Cooks, Kimbles and Fortescue had no knot. The total is still well down on the corresponding date in 2004.
Ruddy turnstone numbers had increased markedly since the previous aerial survey. 15,445 were present bay-wide compared with only 1,845 eight days previously. As with red knot these were split almost equally between the New Jersey and Delaware shores of the bay. These figures confirm ground observations of significant daily arrivals of turnstone over the past week.
The sanderling count of 8240 was already up to the maximum total count for 2004 (which however, was the lowest ever peak count). Unusually, more than half the sanderling were in Delaware – at Slaughter Beach and shores immediately south of there (4435). In recent years, the maximum count of sanderling on the Delaware shores has usually been nearer 2000. It will be interesting to see if this balance of the sanderling population between the two shores of the bay is maintained during the rest of the migration stopover period.
We have not mentioned in previous daily log reports two additional studies which are taking place on Delaware Bay. Veronica D’Amico, a PhD student from Argentina, is collecting blood samples from a proportion of red knots caught for banding. The purpose is to look for internal parasites and avian-borne diseases such as malaria, influenza and encephalitis in the birds. There is some evidence that shorebirds may select a particular non-breeding site related to their immuno-competence, in order to minimise their exposure to parasites and pathogens. It is possible that this is part of the explanation why red knots which come to Delaware Bay do so from such a huge range of non-breeding areas (south-eastern U.S.A., northern Brazil, right down to Argentine and Chilean Tierra del Fuego). The external body condition of the knot is also being examined for feather lice etc.
A team from the University of Georgia is, for the second consecutive year, collecting cloacal swabs from a sample of all species of shorebirds caught. This is part of a worldwide examination program of migratory birds to evaluate their possible role in transmitting diseases. Results to date indicate that shorebirds carry a very low level of such diseases.
Tuesday, May 17, 2005
Up to 200 red knot were reported briefly at Fortescue in the early morning but this had declined to about 40 by 8.00am. Only a handful were present at Reeds Beach in the morning, but this had increased to over 100 by late afternoon. Turnstone numbers seemed to have increased, with a greater proportion of females now present in the population. The early flocks were nearly all males. Sanderling numbers at Fortescue had also increased from 100 to, at least, 500.
Some horseshoe crabs were spawning on each tide at most locations. But numbers were still modest and the overall density is still insufficient to create the desired level of spilled eggs on the surface of the beaches and in the tide edge. It is this surfeit of eggs which is really needed by red knots. Turnstone and sanderling can cope better with a lesser supply of eggs because they are able to dig up eggs that are buried in the beach. Observations of the spawning crabs at high-tide indicated that there were eight males for every female present. So a visual impression of the number of crabs in the tide edge or stranded upturned on the beach as the tide ebbs can give a misleading impression of the level of crab spawning taking place. The dearth of female crabs is partly the result of the selective, and excessive, harvesting of these over the previous 15 years.
The banding team had an energetic day. Nets were set on Reeds Beach at 5.30am in the hope that a few knot had arrived overnight and would at least facilitate a small catch so that the first radio-transmitters could be put on. No sooner had net-setting been completed than a message was received that there were 200 red knot at Fortescue. So the nets were immediately taken up and moved to Fortescue (a three-quarters of an hour drive). By the time we arrived there were only 50 knot present. At the first location the net was set, laughing gulls continuously occupied the catching area and prevented shorebirds from entering it. After slightly altering the net location a good catch was made – 16 red knot (the target species) and a by-catch of 50 turnstone and 143 sanderling.
The team had not been back long at Reeds Beach when late in the afternoon Larry Niles spotted two flocks, each of 50 – 70 red knot roosting on the north end of Reeds Beach. They looked like newly-arrived birds and were resting rather than feeding, even though most of the other shorebirds were actively foraging. Two nets were quickly deployed and after a one hour/25metre "twinkle" by Dick Veitch, 25 red knot and a by-catch of about 200 turnstone was made in a single net. "Twinkling" is the process of gently moving birds along the shoreline towards the catching area. Overall, in the two catches, 34 radio-transmitters were attached to red knot. So, at last, after the red knot catches in Delaware and New Jersey in the last two days the radio-tracking team is in full operation.
The huge pressure of laughing gulls, with at least 4000 forming a thick band along the shore of Reeds Beach, particularly for the first hour or two after dawn, really tested the exclosure. At the peak of the gull population dense patches of birds penetrated into the area but on the whole the area was virtually free from gulls for most of the day – and unfortunately free of shorebirds also! We will test these current designs for another day or two before making further possible modifications.
There have been welcome new arrivals for the shorebird study team. Mark Peck – a member of the team ever since visits commenced in 1997 – arrived from Toronto last night together with a new team member, Jerry Binsfeld. Ines de Lima Serrano do Nascimento, the Head of the national banding scheme and of shorebird studies in Brazil, also arrived today. She has visited Delaware Bay several times and also been heavily involved in those components of the red knot studies that take place in South America.
Monday, May 16, 2005
The Delaware team successfully made a catch of 73 red knots with, additionally, significant numbers of turnstone, dowitchers and even least sandpipers. The weights of the knot were at the low end of the range (100gms) but some individuals were already increasing their weight quite well (up to 140gms) indicating that birds which had arrived a few days ago were obtaining sufficient food in Mispillion Harbor. Thirty radio-transmitters (each weighing 2.9gms) were attached to red knot to facilitate tracking of their daily movements within Delaware Bay and on nearby Atlantic shorelines. The information helps us understand how the birds utilise the food resources at the different locations around the bay and how their night-time locations differ from that used during the day. It also enables the length of time each bird remains at the Delaware Bay stopover site to be calculated.
There are 13 automatic radio-tracking stations erected in New Jersey – 10 on the northern shores of the bay between Matts Landing and Money Island and three on the Atlantic shore and adjacent marshes around Stone Harbor. There are also three radio-tracking stations in and around Mispillion Harbor on the Delaware side of the bay. All are now switched on.
The "scanners" had another busy day with engraved flags recorded on 80 turnstone, 50 sanderling and 10 knot.
It was decided to double the area of the "gull exclosure" on Reeds Beach. The new structure has the poles spaced far more widely to try and encourage the shorebirds to enter the area.
For the record, the weather remained the same! It has been the most windless May we have experienced on Delaware Bay in nine years. But it has remained pretty cool with only Saturday and part of Sunday being warm so far this month.
Sunday, May 15, 2005
There was a further modest increase in the numbers of turnstones on the bay shores. A complete count from the ferry terminal northwards up to Reeds Beach (about 12 miles) during the high tide period revealed a total of 4000 sanderling and 1000 turnstone. Only five red knot were seen.
It was particularly pleasing to see that by far the greatest concentration of sanderling in the Villas area (an area much favoured each year by sanderling) was in the relatively short stretch of beach which is now fenced off from public access for the remainder of the shorebird migration season (up to June 4th). The birds have very quickly learned where they can roost and feed relatively undisturbed, by people and their pets. Volunteer wardens have been manning all the key sites yesterday and today and they reported that the public were most co-operative in complying with the temporary restrictions to access now applying to certain sections of the beaches.
There was better news on red knot from the Delaware side of the bay. Crab spawning has apparently been heavy in Mispillion Harbor and the red knots, which have arrived on the bay, seem to have largely congregated there. It is estimated that there are at least 2500 present, and a catch is apparently planned for Monday.
The "scanners" had another productive day with 116 different birds carrying individually-marked, engraved flags seen. Sixty-eight were turnstone, 46 sanderling and there were just two red knot. Thirty sightings were birds marked in the previous two years that had not previously been sighted this year. Thirty-five were repeat sightings from previous years and fifty-one were first sightings of birds flagged here during the last few days. It is certainly a time-consuming exercise to locate birds with engraved flags, and to get the bird to stay still long enough to read the engraved letters and numbers, in the mixed flocks of shorebirds actively feeding and roosting on the beach.
Saturday, May 14, 2005
The total catch this morning was 112 turnstone and 90 sanderling. An amazing 27 of the turnstone carried bands from previous years, including several from as long ago as May 1998. Many of the birds still had extremely low weights, indicating they had only just arrived on the bay. But the mean weights for both species were also low, indicating that even those birds that had been present for a few days are only gaining weight slowly. This is almost certainly the result of the low level of horseshoe spawning that has taken place this year, resulting in comparatively few eggs being available at present for the shorebirds.
There was little evidence of further significant horseshoe crab spawning at Reeds Beach. But there were reports of some spawning further down the shores between there and the north side of Villas.
The "scanners" had a busy day at a variety of locations and managed to find 45 new engraved-flagged sanderling and turnstone that had originally been marked last year. They also saw a red knot – one of the very few present – with a Brazilian colour-flag (blue) and a white band indicating that the bird had been marked at Lagoa de Peche in southern Brazil. Red knot, however, are still virtually absent from the New Jersey bay shores and even the small flocks of red knot seen in recent days, in saltmarsh habitats at Matts Landing and near Stone Harbor, appear to have dwindled.
The weather was rather more changeable today. During banding activities in the morning there was a cool, south-westerly breeze but by the afternoon it was again calm - and warmer than any previous day. Saturday night was also very warm and hopefully this is leading to an increase in sea temperatures sufficient to trigger a much-needed greater volume of crabs spawning.
Regular observations were made of the gull exclosure during the day. Virtually no gulls and no shorebirds entered the exclosure. In fact there were not many gulls on the beach at all, probably because of the absence of crab eggs, due to little spawning in the previous 24 hours. Consequently, the 1000 sanderling and 900 turnstone had more than enough room to feed (mainly by digging up crag eggs laid at the mid-beach level) and therefore had no need to enter the exclusion area.
Friday, May 13, 2005
Part of the team spent the day searching for other possible high tide roost locations for red knots. No suitable alternative cannon-net catching-site was found. It appears that the red knot which are here and are feeding at low tide on the mudflats at Matts Landing are adjourning to the upper marsh tidal lagoons near Bivalve and to the saltmarshes on the inner parts of Egg Island. The 200-300 red knots feeding on the mudflats on the low tide near Stone Harbor are not currently roosting on the beaches at Stone Harbor point. It seems probable that at high tide they too are moving into a saltmarsh location to roost, with large flocks of dunlin and large-billed dowitchers.
So until there is a significant arrival of red knot from the south, and sufficient horseshoe crab eggs on the bay shores for them to choose to feed there, some aspects of our red knot studies are held up.
The weather in Delaware Bay continues to be generally calm and fine, though the barometric pressure fell throughout the day after reaching a peak of 1029mB. At times there was a little cloud and a moderate wind from the south-east, but nothing to deter migrating birds or prevent horseshoe crabs from spawning. It seems likely that arrivals of red knots, and further significant arrivals of sanderling and turnstone, are not occurring because of unfavourable weather conditions further south, or because the birds have not yet gained sufficient weight in their previous stopover location in northern Brazil. The crab spawning is probably at its current rather low level because of the low sea temperatures – though fine, the days have been cool – and because it is now a period of neap tides. The horseshoe crabs prefer the high spring tides associated with the full moon and new moon periods because this gives them access to a much greater area of beach.
The "scanners" efforts and perseverance were rewarded with a particularly interesting sighting. A turnstone with engraved flag ANH, originally marked here in May last year and seen and photographed in the British Virgin Islands in the Caribbean during the winter, was sighted again on Reeds Beach. The previous day a turnstone which had been originally marked in Bermuda was also sighted. The knot scanners also found, at Matts Landing, a bird originally flagged in Argentina – the third sighting of an Argentine-flagged bird so far this May.
The news on the experimental "gull exclosure" on Reeds Beach was less encouraging. The re-constructed and expanded version was empty of birds for most of the time. However, when the high tide line ran through the area the laughing gulls overcame their inhibitions and entered it in droves. Because no birds had been gleaning horseshoe crab eggs from that part of the beach earlier in the day the amount of food available was particularly attractive to the gulls. The shorebirds, however, were more cautious and although a couple of hundred sanderling fed right up to the poles at the edge of the exclosure area they were reluctant to go under the nylon monofilament wires stretched between posts. Only small groups of sanderling ever entered the exclosure area and then only briefly.
In an attempt to prevent the laughing gull penetration into the exclosure area an additional partial network of nylon monofilament line was erected at a height of only three feet along the seaward side of the exclosure. This had the desired effect of almost eliminating gull movements into the area, but the shorebirds were still excluded too. We are running short of ideas on further modifications to test to try and achieve the objective of allowing shorebirds into the area but keeping gulls out. At present the reverse is easier to achieve! We decided to make no more modifications however until the current structure has been further evaluated. Ideally this should be under conditions where there are many more shorebirds feeding on the beaches and many more crab eggs available. This would lead to higher gull numbers and greater competition between gulls and shorebirds for food. It is under those conditions that the exclusion of gulls could be potentially the most valuable for maximizing the availability of horseshoe crab eggs for shorebirds.
May 12, 2005
The number of shorebirds on Reeds Beach was similar to yesterday – suggesting few new arrivals from the south – but the number of laughing gulls and larger black-backed and herring gulls had increased still further. No comprehensive survey or count of shorebirds was attempted today but the impression formed by the "scanners" was that numbers had not increased markedly. However, greater use of the shore at Cooks and Kimbles was being made by shorebirds during the low tide period, indicating that horseshoe crab egg-laying had now spread to this area as well.
The "scanners" had a field day with extensive observations at a number of locations, sighting many of the sanderling and turnstone flagged yesterday as well as a good number from previous years. Twenty-seven turnstone with engraved flags were seen, 19 of them being returns of birds flagged here last year. Similarly, most of the 24 sanderling seen with engraved flags were last year’s birds, with only 7 being birds that had been flagged the previous day. Red knot – the most important of the study species – with engraved flags are proving extremely difficult to find. This is partly because of the low numbers that have arrived so far but also because those which are present are mostly roosting and feeding at inaccessible locations – Matts Landing and the saltmarshes and creeks near Stone Harbor. An exciting report from yesterday, not included in the previous daily log, was the sighting of a red knot with an engraved, red leg-flag. This flag was put on at Bahia Lomas in the Tierra del Fuego part of southern Chile in February 2004 by the NJ fish and Wildlife team which makes an annual visit to this principal red knot non-breeding area. This individual bird has now been seen twice on successive days - once at Stone Harbor on the Atlantic coast and then at Reed Beach on the bay shore.
The erection of automatic tracking stations along the shores of the bay was completed today. There are six tracking stations on bay shores and three in Stone Harbor. Two have also been deployed in Delaware at, and close to, Mispillion Harbor (the red knot stronghold). All will be switched on as soon as the first knots are caught and have radio transmitters attached to them. Hopefully this will occur in the next few days.
No banding was attempted today, following yesterday’s successful catch of sanderling and turnstone, but everything is ready for a possible attempt at red knot tomorrow. This depends on sufficient birds coming over the horizon in the next 12 hours!
The modified "gull exclosure" was observed at frequent intervals throughout the day, including during both low and high tide periods. It was quite effective at keeping out gulls, but unfortunately almost as successful at excluding shorebirds! This was thought to be because the two latest modifications to the original exclosure have involved setting up the network of nylon monofilament at a lower level (four feet) than originally (eight feet). So late in the afternoon the original structure was completely dismantled and a new and expanded exclosure was constructed. This straddles the area in which most crabs have been laying their eggs and also encompasses the expected high tidelines for the next few days. Tides are gradually reducing to the lowest neap tide, which occurs on Saturday. The distance between the metal posts has now been doubled, to sixty feet. The total size of the new exclosure is 180 feet by 50 feet. The height of the nylon monofilament line stretched between posts has been set at six feet. It is hoped that this "mark 4" exclosure will allow the shorebirds to feed under it but deter most of the gulls.
Wednesday, May 11, 2005
The first attempt to catch shorebirds this year was made, on Reeds Beach. The catching programme has several purposes. The first is to measure the weights of birds over the four-week period during which shorebirds migrate through Delaware Bay. These measurements will indicate whether the birds are gaining sufficient weight in the necessary time, whilst they are at the bay, to fuel them for their final flight to their Arctic breeding-grounds and to meet their energy needs immediately after their arrival there, when food can be scarce.
A second purpose of catching is to re-capture a sample of shorebirds which have been banded in previous years and which have survived and returned. Closely-linked to this, as an alternative method of measuring survival rates, is the need to put individually engraved leg-flags on birds so that they can be re-sighted with the aid of a telescope whilst they remain on the bay this year and when they return in future years. They may also be sighted elsewhere in the flyway on migration, on their Arctic breeding-grounds, or on their non-breeding areas in the Caribbean islands and shores and in South America.
The target today was birds newly-arrived after their migratory journey from the south. At the second attempt two cannon nets were set in the right position on the beach to facilitate the birds accumulating in front of them to feed. At the first setting location the birds just kept walking along the tide edge in a continuous procession with the numbers in the catching area never reaching the optimum target level (50-70 of a species). The prime objective was ruddy turnstone as these were the most newly-arrived species and it was considered likely that an adequate sample of sanderling would inevitably be caught as a by-catch. When a reasonable sample of turnstone had collected in the catching area, and as birds were walking out as fast as new birds were walking in, the nets were fired.
The result was an excellent catch of 37 turnstone, 155 sanderling and three red knot. Twenty-seven of the sanderling, five of the turnstone and one of the red knot carried bands from earlier years' banding activities at Delaware Bay. One turnstone had originally been banded eight years ago, on almost the first catch made at Delaware Bay, in May 1997. Today was the fourth time it had been caught.
The weights were interesting. In all three species the majority of birds were extremely light. The average weights were below the "fat-free" level (ie normal) and were below the weights recorded at, or close to, this date in previous years. It is certainly clear that these birds had just completed a long migratory flight, most probably directly from the northern shores of Brazil (5000km/3000 miles). The exceptionally low mean weight occurred in spite of the weather conditions during at least the latter part of this flight being ideal for migration (calm, clear, no rain or significant headwinds). The mean weights were probably low because almost all the birds in the catch sample had only arrived in the previous day or two. Few birds had been present long enough to regain their normal weights or to start the process of putting on fat for the next stage of their migratory journey.
In terms of numbers of birds present the most significant information today was confirmation that almost all the red knot currently present on the New Jersey side of the bay are feeding on saltmarsh and mudflat habitats. Here they appear to be eating small shellfish (their staple diet at most other locations in the world) and even polychaetes (worms). This strongly suggests that there are still too few horseshoe crab eggs available within Delaware Bay to satisfy their needs. Unlike turnstone, and to a lesser extent sanderling, red knots do not often resort to digging up crab eggs out of the sand. It also suggests, and initial observations confirm this, that it may be a good year for mussel spat.
In May 2003 some red knot exploited this alternative food source which was extremely plentiful that year. There was no mussel spat of any consequence in 2004 but fortunately horseshoe crab eggs were much more plentiful at the time the red knot were on Delaware Bay than they had been the previous year. Three hundred and fifty red knot were present today, all in saltmarsh habitat, at Matts Landing and 200 near Stone Harbor. At both places numbers of red knot have been slowly building up in recent days. In contrast, at Reeds Beach there were still less than 20 red knot and none on the other New Jersey shores of the bay. Two hundred have now apparently arrived in Mispillion Harbor, the prime red knot site on the Delaware side of the bay.
Tuesday, May 10, 2005
Interestingly, whereas a turnstone would dig a hole on its own, and repel intruders whether they be other turnstones or sanderling, sanderling themselves would gather in small groups of up to a dozen birds communally digging into a hollow created by an egg-laying horseshoe crab. They are less well-equipped - the turnstone has a very strong, short bill - for digging so presumably collaborating in getting at the food source is necessary.
David Price and other members of the scanning team spent much of the day trying to read the engraved leg-flags on sanderling to see which birds had survived since last year and returned. They confirmed previous experience that it is much harder to read the engraved flags on sanderling than on red knot, partly because the flags are smaller but mainly because the birds are so active in running up and down between the waves and along the beaches. They managed to read ten engraved flags (black engraving on light green flag) but found that it could take up to 15 minutes to actually read the three engraved letters once a bird with an engraved flag had been encountered.
The second aerial survey for this season of all the bay beaches was carried out in the period after high-tide by Kathy Clark, Jim Dowdell, and Ron Porter. They found that shorebird numbers in the bay overall were still very low. Red knot were almost absent from the beaches (less than 50), there were fewer than a thousand turnstone (most of these were on the Delaware-side of the bay at Port Mahon) and sanderling numbers were remarkably low (around 1500). It is interesting that the concentration of sanderling recorded yesterday in the Villas/Town beach area had dispersed; this was confirmed by the "scanners" (who reported hundreds, not thousands).
Further observations of the gull exclosure indicated that, although having a significant effect on bird distribution on the beach, some gulls, in addition to the shorebirds, were feeding under it at times. In the evening an additional set of nylon monofilament "wires" was therefore added to the structure at half the height of the previous arrangement. This meant that there was a network of nylon monofilament about four feet above the ground and another at about eight feet.
Monday, May 9, 2005
A complete count of shorebirds was carried out from Reeds Beach southward through Cooks, Kimbles, Pierces Point, Rutgers, Norburys Landing, Sunset, Villas, Town Beach, almost to the ferry. Sanderling was the dominant species with 4,000 altogether. Most were in the Villas/Town Beach section but there were 400 at Reeds Beach. The first turnstone had also arrived with 64 in total, 50 on Reeds Beach and the rest scattered in ones and twos. Six red knot were also seen for a short time at Reeds Beach.
Periodically during the morning the birds' reaction to the gull exclosure was monitored. Several times up to 70 sanderling fed within it and twice feeding knot (four and two) walked through it from end-to-end without any apparent concern. The laughing gulls were much more wary, but at times up to a dozen birds were also inside it, but for lesser periods than the shorebirds. It certainly seemed to be having some effect at keeping gulls off that section of the beach.
In the afternoon the whole of the New Jersey team travelled by ferry to the Delaware side of the bay for a 4-7pm meeting of the Delaware Bay Shorebird Technical Review Committee (at the Lewes Ferry Terminal). This meeting finalized the details, and liasion arrangements between the Delaware and New Jersey sides of the bay, of all aspects of shorebird-related fieldwork this May/early June.
Sunday, May 8, 2005
The sea was almost calm all day. No spawning crabs were apparent on the extremely high spring tide when we arrived at 11.00pm on the Saturday night and no crabs were apparent on the Sunday morning tide either. One crab was seen on Reeds Beach on the incoming tide on Sunday evening and there were reports of a couple being seen elsewhere.
Reeds Beach has rarely been so bare of birds in May. There were no laughing gulls and no other gulls. There were no shorebirds feeding anywhere on the beach. At one stage 20 sanderling dropped in but they did not stay long.
Reports from members of the team indicated a few small groups (typically 20) of sanderling on various bay beaches but no turnstone or red knot. There were about 70 red knot at a saltmarsh location at Matts Landing, just beyond Thompsons Beach. Stone Harbor has rather more birds with at least 80, perhaps up to 200 red knot in the marshy creeks. Also 350 sanderling, with an occasional flock of up to 2000, were seen in the ocean area.
Apparently it has been a very cold winter persisting well into the spring. The sea temperature was recently measured at 49°F and apparently it needs to be 53°F before many crabs will come ashore to spawn. Clearly none have done so yet and this is illustrated by the dearth of gulls on the bay shores. It also appears as if shorebird arrivals are late. A great contrast to last year when there was quite heavy crab spawning in early May and good arrivals of birds in good condition. Ironically, last year when all the shorebirds were early at Delaware Bay they were met by an extremely late snowmelt in the Arctic. This year, when the shorebirds are a little late here, the Arctic is apparently already exceptionally snow-free with some wildfowl already back near their breeding grounds!
A prototype gull exclosure was constructed on Sunday afternoon on the north end of Reeds Beach. It is about 60 feet long and 20 feet wide and is set over the high tide wrack (rubbish) and other sections of the top of the beach. It will not be possible to assess whether it is effective at keeping away gulls, but allowing shorebirds in, until some horseshoe crab spawning, to provide food, occurs and significant numbers of birds have arrived. But at least it will be possible to test its abilities to withstand weather and tides in the meantime. The design may need fine-tunning, or even radical re-development, to find the optimum configuration, but if it works several such structures will be deployed at shorebird feeding "hotspots" along the New Jersey shore of the bay.
Dr Humphrey Sitters is currently erecting automatic radio-tracking stations at various locations around the bay. Several are now deployed but not switched on yet. The greatest difficulty is finding owners of property, who mostly aren't occupying them at present, in order to get permission to set up the apparatus.
Ron Porter and David Price, and also Dr Allan Baker and Patricia Gonazales are regularly scanning but so far opportunities are limited by the lack of birds. Nevertheless they have already collected 20 or 30 engraved flag records from the few sanderling and even fewer red knot that are here.