Activities at Delaware Bay (New Jersey and Delaware, USA) in May and early June this year followed a very similar pattern to previous years. The usual international team (8 Canada, 4 Australia, 3 England, 2 Chile, 1 New Zealand, 1 Kenya, 1 Argentina, plus around 12 from USA) assembled at the Reeds Beach base on the New Jersey side of the Bay and a similar team was based at Slaughter Beach, near Mispillion Harbour, in Delaware. Fieldwork operations started on 10th May and continued until 2nd June.
Overall it was an excellent year except that the number of Knot and Turnstone coming to Delaware Bay was lower than in 2010 and lower than in any previous year. Those birds which did arrive were on time and generally in good condition, except for a few low weights in the Turnstones which arrived on 17th and 18th May. Crab spawning continued on the New Jersey side of the Bay at a good level throughout the month, two tides per day, and almost regardless of tide height (springs and neaps). This was because the weather was either calm or the winds were from an easterly direction which meant that the New Jersey shore of Delaware Bay was protected. Horseshoe Crabs will not come to the shore to spawn (around high tide) if there is significant wave action because they get overturned and can be left stranded upside down on the beaches. By about 20th May spilled Horseshoe Crab eggs could easily be seen on the New Jersey bay shore and some dense patches collected in creek mouths and other sheltered places. Birds thus gained weight steadily, uninterrupted by the short, cold, wet, windy spells which have occurred during the middle parts of May in most previous years.
Overall 2,171 birds were banded and flagged or retrapped, in 13 cannon-net catches (2,181 in 17 catches last year). The Red Knot (713) and Turnstone (588) samples were ideally spread at 3 or 4 day intervals between 12th and 30th May. The Sanderling (870) were mainly caught in 4, rather more widely spaced catches (deliberately), between 11th and 31st May. There were more within-season recaptures in Red Knot (25) and in Sanderling (23) than normal. Most Red Knot gained weight at 3 to 5 g per day (one, however, gained 15 g in one day) and most Sanderling gained weight, at 1 to 2 g per day. Peak weights reached by individuals were 210 g for Red Knot, 185 g for Ruddy Turnstone and 110 g for Sanderling.
Finally, to round matters off, the weather was particularly settled for the last 10 days of May, meaning that suitable weather conditions for northward migratory departures were available every day. There were huge emigrations of Dunlin and Short-billed Dowitchers from about May 20th onwards and the first Red Knot/Turnstone/Sanderling left on May 24th - a day earlier than ever previously recorded. At the end of the month it was surprising to see that perhaps 20% of the population of these 3 species still remained, even though their weights were satisfactory. Presumably they were waiting for the appropriate date - an unusual situation since in most previous years birds have been struggling to reach take-off weight and have suitable weather conditions for migration by their preferred date of departure.
It is very disappointing that the Knot and Turnstone populations again showed a further decline this year. This was confirmed by both aerial surveys and by coordinated ground/boat counts. With the Red Knot population at the main site at Bahia Lomas in Chile having reduced from 11,000 to 6,000 according to the usual aerial survey earlier this year it was not unexpected that Knot numbers would decrease. Just under 14,000 were present on the whole Bay at peak. The explanation for this apparent sudden further decrease in population is not clear. It has been suggested that the increased frequency of severe hurricanes (there were 8 this year) in the Caribbean during August/September may be causing the loss of some birds during their southward ocean-crossing from North America to South America. Insufficient is known about Ruddy Turnstone to know what factors are affecting their populations other than the obvious one of the major decline in overall Horseshoe Crab numbers at the Delaware Bay northward stopover.
Five geolocators were retrieved from Red Knot this year. Two had been put on in Florida, 1 in Massachusetts, 1 in Argentina (which had originally been banded in Chile) and only 1 from Delaware Bay itself. However this was a particularly interesting one as it was a bird with a geolocator which was retrieved last year (and replaced with a new one). Its migration in both years was very similar. However one of the Florida birds (where 3 migratory journeys were recorded on the logger put on in early 2010) had changed its migration pattern this year, stopping off in Delaware Bay whereas in 2010 it had flown directly from Florida to Hudson Bay. This bird also, notably, had arrived back in its non-breeding area in Florida (again by direct flight from Canada) at the early date of August 15th. It was still in Florida until the day before we caught it in Delaware Bay (May 21st). The bird from Argentina had flown directly across the South American continent on its northward migration and made its initial stopover in Colombia. Fifty new geolocators were applied to Red Knot at Delaware Bay this year.
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