Wednesday, January 25, 2006

Hybrid Duck

This afternoon I walked around the east end of the National Mall to see if there was anything unusual. The reflecting pool in front of the Capitol was deserted; usually there are plenty of gulls there, but not today. We did have very high winds today so perhaps they took shelter elsewhere.

The National Museum of the American Indian still had the swamp sparrows I had noted earlier, plus a song sparrow. The usual mallard contingent was there as well. Among the mallards there was one unusual-looking bird. The photo is below.

The head is mostly grayish-brown, but with a green stripe curling from the back through the eye area. The back and sides are darker than one would expect from a mallard, but the breast is more finely streaked than a black duck, with a richer coloration. The wing patches (specula) are a bluer color than the surrounding mallards, but still have a noticeable white edging. So what is this bird? My guess is that it is a hybrid, probably mallard X black duck. Such a combination is quite common around here. In fact, I was seeing mallard X black duck hybrids in D.C. several months before I saw an actual black duck, during my first year of birding here.

Birders need to be aware of possible hybrid individuals and stay on the lookout for them. Some hybrids are given names, such as the Lawrence's and Brewster's crosses of the blue-winged and golden-winged warblers. Hybrids can and do show up anywhere one of their constituent species can be. When the two species are relatively easy to distinguish, like the mallard and black duck, hybrids should not add too much extra complexity into the equation. In other cases, the presence of hybrids would make positive identification much more difficult. Hybridization among gulls of the herring gull complex creates special problems, because gulls are not that easy to distinguish to begin with.