15 June 2009

Spectacle on the Delaware Bay

Finally, I'm done with grading and comments and the house renovations are nearing completion. Now I can catch up on a backlog of posts. I'll start out with the promised photos from the horseshoe crab and shorebird spectacle on the Delaware Bay. I headed over to the Delaware Bay in the very predawn on May 24th. Each year around this time (third week of May is usually the peak) horseshoe crabs come ashore to spawn on the beaches of the Bay. The crabs normally come ashore at evening high tides during a full or new moon and the female will leave approximately 80,000 eggs (http://horseshoecrab.org/nh/spawn.html). Conveniently (at least for the shorebirds), this is the time of year when hundreds of thousands of hungry shorebirds arrive in the Bay during their northward migration to the breeding grounds. The shorebirds take advantage of the ready food source in the form of horseshoe crab eggs that have been brought to the surface by the burrowing of subsequent crabs and the waves. Some shorebirds almost double their weight during their short stopover here. Some of the major species of shorebirds utilizing this stopover area are Red Knots, Dunlin, Ruddy Turnstones, Sanderling, and Semipalmated Sandpipers. (Spawning Horseshoe Crabs (Limulus polyphemus) at Sunrise, Mispillion River Inlet, Milford, DE)

Recently it seems that the numbers of spawning crabs have gone down in the Bay
(scientific evidence is spotty at this point because of different counting methods) and with it the populations of dependent shorebirds such as the Red Knot (there is good scientific evidence for the shorebird declines, but not why) . It isn't incredibly surprising that the population of horseshoe crabs started dwindling with increasing harvesting pressure. Really it seems that their breeding success is really a numbers game given the amount of natural mortality. Thousands of adult crabs die during spawning from being "stranded" out of the water and/or being predated. Despite the huge numbers laid, the shorebirds must put a decent dent in the numbers of eggs, not to mention larval mortality which I don't think has been studied. Add to that: pollution in the Bay, harvesting for bait, bleeding mortality for medical use, and human modification of the shoreline and it is a wonder that they are doing as well as they are. In particular, I noticed that the crabs I observed spawning at Mispillion Harbor were having a real problem with the erosion control barriers put in place to protect the houses and roads we insist on building right on the waterfront. Imagine trying to drag that huge, heavy, inflexible shell over all the rocks you see in the above photo, not to mention curbs, berms, roadside ditches, and assorted other erosion control measures... I actually spent a large part of my morning flipping over crabs and returning them to the water, or unwedging crabs that had slid between rocks or curbsides. (Spawning Horseshoe Crabs and Erosion Control, Mispillion River Inlet, Milford, DE)

Mispillion Harbor and the Mispillion River Inlet are actually famous for their concentrations of Red Knots (Calidris canutus). The day I was there, there were approximately 8000-10000 of them out in the Harbor. It was an incredible sight, but unfortunately none were close enough to photograph. However, along the little rocky causeway between the river and the marsh there were quite a few Ruddy Turnstones (Arenaria interpres), with appearances by Willets (Catoptrophorus semipalmatus), Dunlin (Calidris alpina), Semipalmated Sandpipers (Calidris pusilla), and Short-billed Dowitchers (Limnodromus griseus). (Ruddy Turnstone, Mispillion River Inlet, Milford, DE)

(Willet, Mispillion River Inlet, Milford, DE)

(Ruddy Turnstone, Mispillion River Inlet, Milford, DE)

While photographing along that causeway, I also happened to spot and photograph the Ruddy Turnstone pictured here. I could read the green leg flag on this bird in the photograph (XC5) and reported the sighting to the Delaware Shorebird Project(http://www.fw.delaware.gov/Shorebirds/Pages/AboutShorebirdProject.aspx). It turns out that this was the first time this bird had been resighted since it was originally banded at Gandy's Beach, NJ in 2007.

As it turns out, I missed out on the real dawn hot spot that morning, Port Mahon Road. I decided to visit Port Mahon second that morning, which was a big mistake. It was teaming with horseshoe crabs and birds and most certainly would have been better in the early morning when the light was sweet and the tourists few. Very few Red Knots show up along Port Mahon, but the flocks of Ruddy Turnstones, Semipalmated Sandpipers, and Dunlin were very accessible photographically and there were incredibly dense concentrations of crabs. Well, now I know where to go first next year. I'll finish off this post with a few shots from Port Mahon. I didn't get any real great shorebird shots here. A combination of the speeding trucks with boats and tourists disturbing the birds, the harsh light, and the fact that I had to photograph the birds from my car window without a tripod. Positioning my car for any length of time on the mostly one lane road was also difficult. So, I've included one flock shot of Semipalmated Sandpipers just so you can get a feel for it, but realize it isn't my best. (Spawning Horseshoe Crabs, Port Mahon Road, Port Mahon, DE)

(Spawning Horseshoe Crabs
, Port Mahon Road, Port Mahon, DE)

(Spawning Horseshoe Crabs
, Port Mahon Road, Port Mahon, DE)

(Spawning Horseshoe Crabs, Port Mahon Road, Port Mahon, DE)

(Flock of Semipalmated Sandpipers and One Dunlin, Port Mahon Road, Port Mahon, DE)

1 comment:

  1. Awesome! Great photos. I love horseshoe crabs.