While monitoring shorebirds on Mass Audubon’s Tern Island in Chatham last week, I came across an individual bird that illustrated the hemispheric scope of bird migration, and shed some light on the struggles of a threatened Arctic nesting shorebird population.
The bird in question, a Red Knot, had a field-readable flag on its leg placed there by researchers studying their migration ecology, and his unique three-letter code allowed me to trace him to a beach in Delaware, where he was first captured back on May 16.
The Red Knot is a species that migrates between high Arctic nesting areas and wintering areas as far away as the southern tip of South America. We primarily see them in their southbound migration from July through October, where they can be mainly found on tidal flats and outer beaches from Eastham to Chatham. At this time of year they feed on tiny, young mussels, known as mussel spat, as well as small shrimp and other marine invertebrates. They are way pickier than other shorebirds about where they hang out, so you are unlikely to find more than a few away from Chatham, where flocks of 600 or more are possible at places like Tern Island, North Beach, South Beach, and Monomoy.
But in the spring, they are hard to find anywhere in this region - most of them converge on certain beaches in New Jersey and Delaware. And while it may be surprising that anything would go to New Jersey on purpose in such numbers, it turns out the knots flock to these sites to feed on the eggs of thousands and thousands of horseshoe crabs.
It’s hard for us in relatively horseshoe crab-free Massachusetts to imagine the scene on Delaware Bay beaches in May – uncountable hordes of horseshoe crabs clambering over each other to spawn, churning up each other’s eggs in the process. The eggs brought to the surface from the buried nests are then available for Red Knots to eat, and they depend on this abundance of eggs to get them in the right body condition to fly to the arctic and breed successfully. Getting enough eggs to eat is the difference between breeding and not breeding, or even surviving the flight or perishing.
Which brings us to the knot I saw and photographed on Tern Island. It turns out this bird had just been trapped and fitted with the leg flag in Delaware on May 16. Less than a week later he was in Cape Cod. This is odd because once a knot is in Delaware Bay, the routine is to gorge on horseshoe crab eggs, get fat, then fly straight to the arctic – they should not be coming to Cape Cod first. Larry Niles, one of the scientists studying knots and horseshoe crabs, confirmed that they are having a bad year for both horseshoe crabs and Red Knots down there – his data shows that the birds they are capturing are not gaining the minimum amount of weight necessary to migrate and breed successfully this spring. This bird was probably not finding enough horseshoe crab eggs, so came begging to Cape Cod for alternative food sources. All of this points toward a potentially bad year for Red Knot breeding, which could mean fewer knots migrating through Cape Cod later this summer.
If you’re someone who likes to watch shorebirds, and you own a spotting scope or a good telephoto lens, you can help with this important research. Just report the flag color and code for any marked shorebirds you see to http://bandedbirds.org/
You can even bring up a map of the other locations your bird has been seen, which sometimes includes places like Chile and Argentina. And while it may be depressing to learn that a five ounce shorebird is more well-travelled than you are, at least you know you are contributing to an important, hemisphere-wide conservation effort.
