Good horseshoe crab egg densities draw 34,500 Red Knots to the bay

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by Larry Niles (Part 2 of 3)

The best news is a direct consequence of these good conditions, the number of knots and turnstones increased this year. Our season-high estimates show that there are 34,500 knots in the bay and 21,000 ruddy turnstones. These may be the highest counts on the bay in at least 15 years.

Why? At first one would conclude the increased numbers on the bay represent a real increase in the size of the population, but it is not. Shorebirds need time to respond to improving conditions because they are relatively slow breeders, as are most Arctic breeders. Knot numbers on Delaware Bay basically depend on the availability of crab eggs. In bad years, numbers go down because birds come to the bay and leave quickly.

This was the case last year. Egg densities during May plummeted to less than a few thousand-eggs/meter2.  Knots banded in Delaware Bay were resighted days after release in other stopovers like Cape Cod. Consequently, our Red Knot count on the bay fell from 24,500 in 2016 to 17,500 in 2018. We assumed this was not a real decrease in numbers, but the result of birds leaving right after finding eggs too scarce or competition too intense on the bay.

This year we found good egg densities, and birds staying long enough to be counted. The aerial and ground counts detect only a portion of that number depending on the total number of red knots and the egg density. The longer birds stay, the greater the proportions of the total are seen on one day. So this year we had good egg densities, good weights, and good numbers. It was one of the best of seasons in recent memory.

Dr. Larry Niles has led efforts to protect red knots and horseshoe crabs for over 30 years.

A red knot flock near Straight Creek on Egg Island in NJ. This flock was one of several on Egg island that totaled over 13,000, a third of the entire bay flock. The birds use this remote marsh as a staging site before flying off to the Arctic.
Shorebirds on Cooks Creek Inlet seen from Cooks Beach. The birds practically reside in this inlet and the four others that flow from the marsh behind the beaches from Reeds Beach to Pierce’s Point.
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  1. Larry,

    I think there may be typo in your posting “Consequently, our Red Knot count on the bay fell from 24,500 in 2016 to 17,500 in 2018.” I think you meant 2017 and not 2018.

    Love the work you and your team are doing. My buddy and I stumbled on the team in Fortescue on May 24th, but didn’t get to see the banding as the cannon firing was called off.

    A few weeks later (June 12th) we found three red knots closer to home – Sandy Hook.

    All the best,

    Karl

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