Dead Bird Quiz answers

1 11 2012

Thanks to Wouter, super dead-bird-identifier, for submitting answers on this quiz! Especially since Bird B is nearly skeletal and Wouter is quite an expert in seabird osteology.

Bird A presents a particular kind of challenge: the falling apart bird. What we have here is a partial head and a set of wings. It’s always possible that the parts are actually from more than one carcass and just got jumbled together. We can reserve this explanation if we can find no single species that fits both the head and wings of this carcass. So, to assess what we have: a broad, duck-like bill attached to part of a dark capped, white cheeked head. What ducks have a dark cap and a white cheek? All three of our scoter species have some degree of white cheek, but only the Black Scoter has a bill shape and profile that roughly matches the one in our Bird A. Black Scoters though tend to have something of a brownish wash to the cheek, unlike the bright white we see in Bird A.

Adult male Ruddy Duck showing some breeding blue on the bill. Clean white cheeks are evident here.

Black scoters show a less stark contrast between dark cap and white cheek.

The white cheek in male Ruddy Ducks is set off quite starkly from the dark cap. This is consistent with the coloration in our Bird A. Juvenile Ruddy Ducks and females have a much muddier look to the cheek, so we can rule those out in this case. Now, about those wings. I admit that the grayish color with faint spots of chestnut made me think of something like a night heron.  We don’t have a wing chord on Bird A since it was not found on a SEANET survey, but a night heron’s wing is almost twice the size of a Ruddy Duck’s, and, roughly speaking, the wings in the photo of Bird A seem closer to Ruddy Duck size than heron size. So, could these wings actually be a Ruddy Duck’s? While breeding male Ruddy Ducks have a reddish cast to the wing (hence the species’ name), in its non-breeding plumage, the male’s wing takes on a darker, gray or brown cast. Check out this image of a male Ruddy Duck wing from the Slater Museum and see what you think. Any other ideas for what it might be?

Bird B presents another challenge: the mostly skeletal bird. This carcass is severely weathered, and essentially no useful plumage characteristics remain. There are some useful features here that can get us quite far. The foot, at first glance, appears unwebbed with “talons” that might make one think of a raptor. On closer inspection, however, some tattered, leathery remnants of foot webs do remain, and in fact are present between all four toes. This is the hallmark of the pouchbill group of seabirds, including gannets, cormorants and pelicans.

What’s left of the fully webbed foot of Bird B.

The other feature that tells us this is a pouchbill is the arrangement of the clavicles, or collarbones. In birds, the clavicles are joined at the center in a v-shaped structure called the furcula (or “wishbone” in common parlance). In most birds, the furcula is not attached to the sternum (breastbone), but in pouchbills, it is quite firmly fused. This adaptation seems especially fitting in the gannets, which plunge dive for food from great heights. The stability provided by a fused furcula/sternum helps them withstand the force of impact with the water’s surface.
So, within the pouchbills, the most likely candidates for a bird found in Maine would be Northern Gannet and cormorant. The only measurement we have on this bird is the tarsus, reported as 50mm. This would be small even for a Double-crested Cormorant, and very small indeed for either a Great Cormorant or a Northern Gannet. I agree with Wouter on this one: cormorant is most likely, but it’s difficult to say for sure which species. Given the apparent small size, and the general rarity of Great Cormorants on SEANET beaches, I might wager a small amount of money on Double-crested. But only a small amount.




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