Florida Puzzler perplexes Seanetters (Dead Bird Quiz answers)

31 07 2009

Looks like Seanetters generally were as stumped by this dead bird as our Florida contingent was. It’s always particularly difficult to i.d. skeletal remains since just about all the usual field marks have been obliterated. The skin of the unfeathered regions weathers away, and the keratin sheath that gives the bill its characteristic appearance is gone. In cases like this, it’s easy to feel adrift. Our unfortunate Shell Key specimen is, in fact, a Northern Gannet. Now, we must get to work figuring out how one might tell.

The mystery dead bird: a Northern Gannet

The mystery dead bird: a Northern Gannet

Take a look at this photo of a Common Loon’s bill (courtesy of an excellent website on seabird bones: http://www.shearwater.nl/seabird-osteology/). No one guessed loon, incidentally, but SEANET does not have any photos of heron skulls on hand, alas. The fundamental difference one should note between the loon and our Gannet friend is the lack of nostrils in the bill of the Gannet. The Gannets and other pouchbills, like cormorants and pelicans, lost their external nostrils over evolutionary time and only a small opening in the bone at the base of the bill remains. Once you’ve determined that the bird is a pouchbill based on lack of nostrils, it’s a matter of comparing the bill profile. Pelicans are so bizarrely distinctive that we can exclude them out of hand, but cormorants are still a possibility. Upon closer examination, however, one notes that cormorants have a more slender bill with a much more prominent hook at the bill tip–nearly a 90 degree angle. So we can be pretty confident that this guy is, in fact, a Northern Gannet, and based on the dark plumage, it’s a juvenile.

Common Loon skull; note the presence of nostrils in the bill

Common Loon skull; note the presence of nostrils in the bill

Oh, wait, what’s that you say? The feet weren’t webbed? True, by the time the specimen was found, no webs were present. But consider the state of the carcass. No soft tissue is left whatsoever, and what are foot webs but thin, fleshy triangles? They would long since have rotted away leaving only the skeletal toes lending it the appearance of a heronish sort of bird. It’s largely unexplored country, this land of seabird forensics, and this has been a particularly good case. Thanks for playing Seanetters!

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