Delaware Bay, Delaware Bay 2011, shorebird ecology

what we still don’t know

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Pervious Post

Our work here on Delaware Bay has gone into hyper drive.  Surveys nearly everyday just after dawn, then trapping  and scanning the rest of the day.  As with all other years, Mandy and I are indebted to the volunteers that have come to the bay from nearby and those from South America, Australia, Great Britain.  This year we even had a volunteer from Kenya, Chege Wa Kariukiour banding team having dinner

The knots have voted with their wings throughout the month.  First in New Jersey, then to Delaware, then back again all in the search of the best feeding conditions for eggs. The birds (and us) have been blessed with settled weather again this year, the third in as many years.   The birds are gaining weights at good rates, and we hope to see at least a modestly-successful departure (however, at a population level that is as much as 90% below historic levels).

The settled weather has helped overcome the lack of any improvement in the number of breeding crabs and eggs.  This cannot last long – truly something needs to be done to avoid tragedy in coming years.  Since 1997, when our intensive study first began, we have had weather that has stopped horseshoe crab egg laying for as long as a week, in all but the last three years.   These last three years of settled weather masks the lack of improvement in crabs as does the tragically low number of shorebirds which reduces demand.The number of mature horseshoe crabs in a survey trawl done by Virginia Tech. The graphs is sanctioned by the Atlantic States Marine Fish Commission and shows no improvement over the last 6 years.

With no improvement in crab numbers and egg densities, a bad year would be a disaster for the birds. We need more crabs to overcome these natural variations in suitable breeding weather and to do this we need to stop the harvest, stop the bleeding of female crabs and significantly reduce bleeding mortality overall until there is a responsible solution to the lack of recovery.  Doing anything else at this stage is irresponsible.

On a more positive note we have recaptured four red knots with geolocators.   The early mapping from the birds is as stunning as the birds I’ve reported about here and there.  We are trying to catch long-distance migrant red knots with geolocators because we have so few, but yesterday we caught a Florida wintering knot that told an intriguing ecological storyRed knot 2AX with a geolocator.

Ever since the early days of work on red knot (the Brits call it “knottery”) here in the US, the prevailing theory held that Florida winterers bred in a different location then those wintering in Tierra del Fuego.  It stood to reason because TDF birds were slightly smaller and their molt schedule was different.  Red knots flying to TDF molt their flight feathers in TDF while birds wintering Florida and other southeast areas tend to molt on the way to the wintering area.  Ultimately, this means distinct breeding populations; otherwise, these morphological differences could not be maintained.  The guess was short-distance birds bred west of the TDF birds in the Canadian ArcticA preliminary map of the track recorded by red knot 2AX’s geolocator ( map by Ron Porter)

But the red knot 2AX (its leg flag id) wintered in Indian Shores, Florida, came to Delaware Bay then bred on Southampton Island, Nunavut, exactly in the same place where two TDF winterers with geolocators bred.

How can two morphologically distinct populations breed in the same area?  How do they maintain separateness in the same place?  The geolocators have shown us much, but most of all they are showing us what we don’t know of one of the most studied birds on the planet.

 

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