The Red Knots “Vote with their Wings”
Clive Minton is fond of saying, “the knots vote with their wings” as a way of saying knots concentrate in the best places for knots. Of course it’s true, animals move to the habitats they find most suitable, nature leaves little room for anything but. Sometimes however, animals use a habitat only because they have little choice — in other words, they are making the best of a bad situation. The job of a good wildlife biologist is to understand the difference. Unfortunately, it’s often not obvious.
In all the places studied by this author — Tierra del Fuego, the Arctic, and many places in between — knots distinguish themselves as highly selective habitat specialists. There are many practical reasons for this: usually knots occur in flocks and thus require more space than many other species. More importantly, as they put on weight for their incredibly long-distance flights, they often push the limit of safe wing-loading (body weight to wing area). This makes them vulnerable to predators, both real and imagined. They need more flying space, more space for advance warning of a predator’s presence. They demand special roost habitats as well, especially night roosts that are free from disturbance and have good sight distances. Altogether they need more.
In Delaware Bay, they need all this, but above all they need good horseshoe crab egg densities. In the mid 2000’s when shorebird numbers were high, the demand for those eggs exceeded the production from the rapidly diminishing crab population. Knots wandered the bay like homeless refugees. Competition for eggs drew tens of thousands of birds to places unused by knots in healthier times.
Mispillion Harbor, Delaware, for example, in some years supported much of the knot population in the Bay because it acts like a funnel-trap for crabs. Crabs wandered into the harbor through long stone jetties finding themselves in crab breeding heaven, sandy shoals in a closed space, free from wind-generated waves that normally leave them upside down. The egg-laying frenzy caused eggs to reach epic densities, thus preparing many shorebirds for their onward journey to the Arctic. Tens of thousands of shorebird packed into Mispillion Harbor in densities so high that one could smell ammonia off-gassing from the amount of bird waste.
But for knots, Mispillion left a lot to be desired. The same jetties that protect the inner harbor from wind-driven waves also provide low-flying raptors the cover to pounce on flocks before they can easily react. Fat birds make easy prey for peregrine falcons, who themselves struggle to keep up with the insatiable hunger of rapidly growing chicks.
But even as shorebird numbers fell in response to the reduced crab numbers, egg densities improved in other places. Knots reassessed their choices and voted with their wings.
This is why this year’s high count of red knots on the New Jersey side of the Bay are so important. Two days ago, Mark Peck, Joe Smith and I flew the entire Bay to count knots, ruddy turnstones and sanderlings. We counted over 24,000 knots, with 21,000 of these using the beaches managed by the many groups that take part in shorebird management on the New Jersey shore of Delaware Bay.
I am not saying this is a competition between two states — I’m saying the numbers serve as assurance that all our hard work is paying off. It’s a confirmation that the beach restoration projects, the Shorebird Stewards project, the reTURN the Favor crab rescue project, and more are bearing fruit. These coordinated strategies are led by Conserve Wildlife Foundation of New Jersey, American Littoral Society, Manomet Center for Conservation Sciences, New Jersey Audubon Society, the Wetlands Institute, Citizens United to Protect the Maurice River, The Nature Conservancy, as well as Downe Township, Maurice River Township, Middle Township and the Division of Fish and Wildlife, New Jersey Department of Environmental Protection. This work is funded by the US Department of Interior, Fish and Wildlife Service, the National Fish and Wildlife Foundation and the Willliam Penn Foundation. Good work all!
We now near the end of the stopover season at Delaware Bay. Three days of southerly winds are proving irresistible for many birds. Nearly two-thirds have left and the rest will be gone in a few days. Thanks to the people who love birds and the residents of the Bay, they leave well-prepared for the next stage of their challenging and inspiring lives.