The decimation of ducks

4 03 2014
A sampler pack of scoter wings mostly with attached sternae found in Brewster MA. (photo: Diana Gaumond).

A sampler pack of scoter wings mostly with attached sternae found in Brewster MA. (photo: Diana Gaumond).

Winter is a grand time for viewing sea ducks near shore. Along my SEANET route, I routinely see bufflehead, common eider, scaup, common goldeneye, red-breasted merganser, and a handful of other occasional visitors. Not surprising then, that winter is also the time that we see the peak of duck mortality along the beaches as well. This winter, it looks like we may be seeing an uptick above typuical mortality among white-winged scoters (WWSC) on Cape Cod in particular. A quick glance at our numbers shows somewhere between double and triple the number of WWSC we saw last winter on SEANET beaches (though that number was never very large itself–fewer than a dozen.) Outside SEANET surveys, we have also been getting reports from Doug McNair, who surveys the outer Cape independently, that WWSC mortality seems well above normal.

Rare intact WWSC found by Warren Mumford in Chatham, MA.

Rare intact WWSC found by Warren Mumford in Chatham, MA.

One thing we tend to notice in duck carcasses is their incomplete nature. While other birds are often found intact, most duck species seem to be found in pieces. Doug raised the question of whether this might be anthropogenic; perhaps hunters strip off the breast meat and toss away the rest of the carcass? I can’t know for sure, but having looked at many pictures of carcasses in various states of disarray, it seems, to my mind, more likely that ducks turn up well scavenged in the average way, but that perhaps ducks are tastier than other carcasses?

And here we see a scoter head, spinal column and foot striking out on their own. (Photo by Jack Hooper).

And here we see a scoter head and neck striking out on their own. (Photo by Jack Hooper).

[I don’t have a clear answer on this, but in tracking individual carcasses over time on SEANET beaches, there does tend to be a typical pattern to their gradual dissipation. First, the entrails are dug out (typical gull behavior, that). Then, the pectoral muscles are stripped from the sternum. As the carcass further decomposes, the wings tend to stay with the sternu, the head goes off with the neck vertebrae, and the ribs, united with the lower vertebrae and fused pelvis eventually drop the legs and roll off by themselves. Given enough time, it appears, all carcasses (or most, anyway) will weather down to the most durable parts: bon, and the strong primary flight feathers that anchor into the bone.  This is merely my personal observation at this point, but it does give me yet another little project to delve into when time permits. I welcome your thoughts on what organisms are doing this stripping away of the meat. On my beach, I suspect the gulls. On southern beaches, I ave been impressed with the diligent scavenging of the ghost crabs. But people may be involved in certain cases too. Have any observations, Seanetters and other beach enthusiasts?

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