Delaware Bay, on the east coast of America, is positioned on
the West Atlantic Flyway and is the final staging area for many thousands of waders
on their migration from their South American wintering grounds to their Arctic breeding
grounds. In spring, the Bay is also home to Horseshoe Crabs. These prehistoric-looking
creatures spawn on the beaches in their thousands and their tiny eggs are
full of protein – just what hungry waders need to replenish their body fat and
to provide them with enough energy to complete their journey north.
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| The Horseshoe Crab eggs that the birds rely on. Photo by Ruth Walker |
Unfortunately, for a number of complex reasons, the
shorebird populations have diminished in recent years. As a result, in the
mid-1990’s,
Wash Wader Ringing Group members helped American scientists
to establish the
Delaware Shorebird Project. The project aims to research and
monitor the health of the wader populations on the Delaware side of the Bay in
order to better understand the connection between the birds, Delaware Bay and
the Horseshoe Crabs. A sister project runs concurrently on the New Jersey side
of the Bay. The birds use both sides of the Bay to feed, often swapping shores
to avoid inclement weather. The data gathered are helping to identify and
protect the resources that are so critical to the success of the wader
migration. In part due to the work of the project, the key target species for
the project, Red Knot, has recently been officially recognised as ‘threatened’
by the US Fish & Wildlife Service.
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| Red Knot. Photo by Ruth Walker |
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| Location of Delaware Bay on the Red Knot's spring migration route |
A number of BTO ringers, including BTO staff, still travel
out to Delaware each May using their holiday time to volunteer alongside other
researchers from around the world on this important project. The study aims to
catch and fit individually coded colour flags to 350 individuals of each target
species each year: Red Knot, Ruddy Turnstone, Sanderling (all of which are
colour flagged) and Semi-palmated Sandpiper (though these are not flagged on
the Delaware side of the Bay). Samples of Dunlin and Short-billed Dowitcher are
also ringed and measured if caught. During their time in the Bay, birds can double
their body weight and therefore catching birds throughout the season is vital
to ascertain their fitness levels. In order to survive their migration, it is
thought that Red Knot need to weigh at least 180g when they depart (having
arrived a couple of weeks earlier weighing 110-120g).
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| The very similar looking Semi-palmated Sandpiper (left) and Sanderling (right). Photo by Ruth Walker |
We aim to ensure that approximately 10% of the Red Knot
population passing through the Bay are flagged, along with smaller percentages
of Ruddy Turnstone, Sanderling and Semi-palmated Sandpipers. Because waders are
global travellers, flagging projects are undertaken in a number of different
countries. The flag colour indicates the country the bird was flagged in, so
birds caught in Delaware have a green flag, but we also see birds with red
(Chile), orange (Argentina), blue (Brazil) and white (Arctic) flags . We attempt
to catch approximately every three days so that we have weight samples throughout
the stopover period, with the rest of the time spent counting the numbers of
birds using each of the beaches each day, re-sighting the colour-flagged birds
as well as the seemingly endless task of entering and checking all of the data.
Re-sighting colour-flagged birds not only gives information on arrival and
leaving dates and movements of individual birds within the Bay, but also information
on survival and the total number of birds using the Bay.
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| An American-ringed Ruddy Turnstone foraging. Photo by Ruth Walker |
This year, 362 Red Knot were caught, along with 284 Ruddy
Turnstone, 75 Sanderling, 407 Semi-palmated Sandpipers, 472 Dunlin and 78
Short-billed Dowitchers. It was very pleasing to see that of the Red Knot
ringed during the final catch of the season, 74% weighed more than 180g, 23% were
over 200g with the heaviest bird weighing in at a whopping 228.6g! Thankfully,
only 4% weighed less than 150g and would need to remain for longer in the Bay.
As the birds departed the Bay, so did the BTO staff and
other volunteers. We look forward to catching up with the birds again next
year!
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