Delaware Bay Shorebird Season – Update 2

Dr. Larry Niles

May 19, 2021

Dear Team,  The status of the stopover remains a mystery.

Yesterday we knew of about 3000 knots and less than 2000 ruddy turnstones on both sides of the bay. This is less than half of what Clive and I would normally see in the morning’s reccis at this time, but just for the area from Pierce’s beach to Reeds Beach. In 2017 and 2018, we saw over 7000 red knots and 7000 ruddy turnstones in the same place, so numbers for both species are way down.

So, why are numbers so far below normal? One answer may be how last year unfolded. In 2020, Stephanie and I saw less than 1000 knots by this time on the Bayshore, but over 6000 at Stone Harbor because the crab spawn failed from water too cold for spawning. We counted 19,397 knots in the baywide count – about 10,000 lower than the previous few years, when numbers went above 30k. There was no aerial count because of COVID restrictions that year, but the estimated number based on resighting was also down by about 10k.

But the season unfolded horribly for knots. The horseshoe crabs did not spawn in great numbers until the end of June, so most knots failed to accumulate weight. Most of the 19,397 knots we saw left by the 23rd, and of the 6000 birds that stayed to the end of May, only 30% reached 180 grams.

This collapse of horseshoe crab spawning occurred in the early 2000s because of both cold water and the overharvest of crabs. Then knot numbers dropped dramatically and only gradually recovered but over the next decade. Some part of this decline was the result of mortality and lack of production, which eventually returned to normal. Another part of the recovery was because the birds that avoided the bay after experiencing few eggs in subsequent years gradually returned.

So this year the decline may be a result of last year.

But the situation may be a result of other factors. David Mizrahi reports a similar situation for Semi Sandpiper, finding few in the main concentration areas like Fortescue Beach and Heislerville Impoundments. They too suffered the lack of eggs of in 2020 but we would not expect this kind of reduction in numbers.

Weather patterns in the Southeast may also be causing this decline, holding up migrants because of adverse winds. See this weather system that has been guiding winds at 250 m high since the 12th and very likely impeding northward migration. The winds aloft today are still from the north, so it doesn’t look much better.

Finally, the invasive peregrine falcons managed by NJ Fish and Wildlife are having a much greater impact on the much-reduced numbers of shorebirds. Each day the birds are hunted down by nesting peregrines. Two days ago, we missed our catch of knots because of repeated attacks from peregrines, probably from the towers maintained on the Atlantic side. Yesterday the flock disappeared for the entire day after repeated early morning attacks. Peregrines are not native to the coast of NJ. They are only here because of management, which started in the 1980s to help restore the population (I was one of the young biologists doing the restoring and led the project for the Division for years). Now they are restored to many habitats – bridges, buildings. The towers are of little value to the population. The substantial influence of peregrines on shorebirds on both the east coast and west coast of the US is well documented and doesn’t belong in this ecosystem except in migration.

On the brighter side, this year’s crab spawn is decent and may improve with the coming daytime high tides gaining height until May 23. Unfortunately, the full moon tide occurs at the end of the month, so the birds may not be able to take advantage of those huge tides and the likely peak of crab spawning. Generally, it seems crabs spawning may be equal to a normal year even though it has been impeded by cool air temperatures at night, driving water temperature below the threshold for crab spawning.

Brighter still, the food has been glorious and abundant thanks to the volunteer cooks from Citizens United. Our days are much longer as we continue to search for birds, dig eggs, and trap birds, and a good meal helps us recover for the next day.

Yesterday we heard from Henrietta that the Delaware Folks caught for the first time with just their home team – 65 knots and turnstones. We also made a small catch of sanderlings for the National Zoo staff as part of the new Delaware Bay exhibit in the newly renovated Birdhouse. See this video on the progress.

Thanks,  Larry and the Delaware Bay team.