In May 2012 Ruth Walker, an Ecologist from our Derbyshire office in Hathersage, travelled to Delaware Bay in the United States to make an international contribution to an important conservation initiative for red knot and other waders. Ruth, who specialises in ornithology for BSG, is a bird ringer and here she provides a summary of this impressive conservation project.
Red knot, along with many other shorebirds, face threats and pressures throughout their ranges including predators, toxic algae, unpredictable food resources, human disturbance, coastal development, climate change and sea-level rise. In recent years, scientists have come to realise that in order to protect migratory species, maintaining just one part of their range such as their breeding grounds, is no longer enough. For many of our fast-declining bird species, impacts on their staging and wintering sites are likely to be key factors affecting their populations.
Delaware Bay, an estuary spanning more than 212km², is the largest and most important migratory bird stopover point on the Atlantic Flyway [i] and is considered to be a globally important wetland. In spring the Bay, which lies between the States of Delaware and New Jersey, plays host to hundreds of thousands of migrating shorebirds moving between their South American / South-eastern US wintering grounds and their breeding grounds in the Arctic.
The Bay is also home to horseshoe crabs. In the spring, these prehistoric creatures spawn on the beaches in their millions and it is their tiny, protein filled, green eggs that attract the shorebirds. Horseshoe crabs are used as bait by conch fishermen, who prefer the larger females. Back in the 1990s, the industry was unregulated, leading to overfishing of the crabs. The resulting decline in the horseshoe crab population was such that the numbers of eggs produced was not sufficient to feed the thousands of shorebirds that relied on them. The result was a dramatic decline in red knot numbers.
The Delaware Shorebird Project
The plight of the red knot led to the regulation of the fishing industry and the establishment, in 1997, of the Delaware Shorebird Project [ii]. The project was established to research and monitor the health of the shorebird populations in order to better understand the connection between the birds, the Bay and the horseshoe crabs. The project works in partnership with the British Trust for Ornithology [iii] and the Wash Wader Ringing Group [iv] and it is through the latter that Ruth was able to join the project for two weeks this May. A sister project, the Delaware Bay Shorebird Project [v], runs concurrently on the New Jersey side of Delaware Bay. The birds use both sides of the Bay to feed, often swapping shores to avoid inclement weather. Having data from both sides is crucial for researchers to gain a full picture of the state of the shorebird populations using the Bay.
Ruth was involved in catching the birds, ringing (placing a small, uniquely identifiable, metal ring onto the bird’s leg) and flagging (placing a small flag with a unique code that is readable from a distance, onto the bird’s leg) them. The aim of the project is for the Delaware and New Jersey teams to each catch 350 individuals of each target species each year. Target species are red knot, ruddy turnstone, sanderling and semipalmated sandpiper. Every three days or so, samples of 50 birds of each species are caught.
The team also visits key beaches along the Bay shore, including Back Beach in Misspilion Harbour, where the largest numbers of birds congregate, to count the birds and attempt to read leg flags using telescopes. Re-sighting colour flagged birds gives information on arrival and leaving dates of individual birds, their movements within the Bay and information on survival of individual birds.
Approximately 10% of the red knot population passing through the Bay is estimated to be flagged, along with smaller percentages of other birds. Flagging projects take place in a number of different countries; the flag colour indicates which country the bird was flagged in. In the US, lime coloured flags are used, Canada uses white, Argentina orange, Brazil blue and Chile red. Counts are also taken of knot and turnstone to ascertain how many birds in the group are flagged (e.g. 50 clearly visible birds of one species will be counted and the number of flags noted). Researchers can use this data to calculate what percentage of the population is flagged, which in turn can be used to estimate population numbers.
Conservation work of global importance
The work done by the Delaware Shorebird Project and the State of Delaware’s Department of Natural Resources and Environmental Control (DNREC) (amongst others) is helping to improve the conditions in Delaware Bay for shorebirds and is increasing awareness of, and encouraging measures to prevent disturbance to, shorebirds whilst they are in the Bay. Today, the horseshoe crab populations are showing signs of recovery and the red knot population using Delaware Bay is stabilising. Recovery of the population may take a little longer, but for now, the monitoring and protection of shorebirds in Delaware Bay is helping to reverse the decline of an iconic species by ensuring that they have a safe haven to stop and re-fuel before completing the journey to their breeding grounds in the Arctic. This sort of integrated scientific effort provides a good example of how conservationists across huge areas can collaborate to understand how to effectively conserve important bird populations.