Saturday, June 12, 2010

Horseshoe Crabs & Shorebirds

Over the past two Saturdays I've pedaled down to Plum Beach in search of Horseshoe Crabs and shorebirds.

The spawning season for Atlantic Horseshoe Crabs and northbound migrating shorebirds have been inextricably linked for tens of thousands of years. Most shorebird species are long distant migrants and horseshoe crab eggs are an important food source during stopovers when heading to their arctic breeding grounds. During the crab's spring breeding cycle large numbers of shorebirds and seabirds can be found feasting on the eggs along NYC beaches. Plum Beach is one of these locations. If you look closely in this photograph, you can see lines of pale green eggs running parallel to the high-tide mark. These are eggs that have been exposed by the tide, making them available to hungry birds.

Last Saturday I met Heydi there at 6am and it appeared that we timed our visit perfectly. Horseshoe Crabs were found all up and down the beach and shorebird numbers were very high compared to the day before. When I spoke with Shane he said he found only 50 Semipalmated Sandpipers on Friday. On Saturday I estimated there were around 1200 shorebirds. The flocks were primarily composed of Semipalmated Sandpipers, but our final morning list contained Black-bellied Plover, Semipalmated Plover, American Oystercatcher, Willet, Sanderling, Western Sandpiper, White-rumped Sandpiper, Dunlin and Short-billed Dowitcher. In addition, there were large numbers of Laughing Gulls feasting on the eggs. Least and Common Terns dove for fish just offshore. Here's a short video of one mixed flock of shorebirds on the low-tide mudflat.

video

Unfortunately, all is not rosy with this avian-"crab" relationship. Due to over harvesting and habitat destruction, horseshoe crab numbers have plummeted. PBS produced an excellent documentary about this issue which can be seen online here. In an effort to understand Horseshoe Crab movements the US Fish & Wildlife Service and US Geologic Survey have been tagging individuals from various locations. This past Saturday Heydi and I located one of the tagged crabs at Plum Beach. I submitted the tag and location data and will let you know when I find out where this individual was originally captured.

Plodding along on dry land, Horseshoe Crabs appear ungainly and clumsy. I frequently find them turned over on their backs where they struggle helplessly to right themselves. If left on their backs, they will eventually die. I'm not sure how they end up that way and if it is ignorant people who flip them over, but Heydi and I rescued a couple of dozen over two Saturdays. If you ever spot one on its back, just pick it up by the shell (http://www.horseshoecrab.org/act/flipem.html), carry it down to the water and place it right-side up. In contrast to this uncoordinated image, I watched a large number of them swimming on the incoming tide within Plum Beach's tidal marsh. The speed and agility of these living dinosaurs was remarkable:

video

Finally, here's a short slideshow of some images I shot at Plum Beach and Floyd Bennett Field:

5 comments:

OpposableChums said...

Amazing pix and story. Thanks.

Matthew said...

Rob, I understand that picking them up by the tail or telson is not recommended because it can damage the optical sensors that are there. This from the just flip 'em campaign at horseshoecrab.org and from personal conversation with rangers at JBWR, who both say the uncrabs should be handled by the edges of the shell.
http://www.horseshoecrab.org/act/flipem.html

Rob Jett said...

Matt,

Thanks for the info. I'll update the post.

Beth in NYC said...

Rob, I've been intending to go to Plum Beach for just the same reason. Do you think it's safe for a woman with a camera and large lens to be there alone?

Rob Jett said...

I do believe that Plum Beach is a very safe location.

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