Hi all,
I saw some photos of an immature YELLOW-HEADED BLACKBIRD that a student from College of the Atlantic, Jordan Chalfant, found 28 August while working on Seal Island (thanks to Rich MacDonald for relaying the pix). This is a really neat find. There have been just a couple seen in Maine each year in the past couple of years.
Yellow-headed Blackbird has a long history of vagrancy to the East Coast and beyond (e.g. Bermuda and even, if natural vagrants, Europe). During the 1980s after I moved to New England, it seemed expected that one might see a few in fall or (less routinely) spring. But by the late 1980s and through the 1990s, up until recently, it became a very rare bird. In the past few years, there has been a slight uptick in records in New England, however.
I was curious about this pattern and thought I'd share some thoughts and speculation on the change in status.
Yellow-headed Blackbird is a moderate distance migrant, with populations east of the Rockies, e.g. the prairies, migrating the farthest and wintering in central and southern Mexico. They mainly leave in late August and arrive on the wintering grounds by late September (i.e. they migrate earlier than most other blackbirds). The birds west of the Rockies, mainly in widely scattered populations, typically go no farther south than northwest Mexico. Roughly speaking, birds east and west of the Rockies differ in size, migration routes, and wintering areas; yet no subspecies are recognized and the birds appear similar.
My guess is that vagrants to the east come from the long distance migrants, the prairie populations. Those would seem the most susceptible to being driven long-distances north and east of their intended migration routes in the fall. If most vagrants eastward are from that area, then it is interesting that surveys in North Dakota showed populations dropping by half from 1981-82 to 1990. The high numbers in the early 1980s were almost 5 times a previous estimate from 1967; so there was a big spike up in the early 1980s. Such fluctuations could be due to drought conditions (or lack of them), habitat availability, and other factors (loss of wintering habitat in south-central Mexico?). It seems interesting that vagrants to the Northeast followed a similar trend, greater in the late 1970s to early 1980s, then dropping off through the 1990s. I don't know if current populations are on the upswing or whether the current weak trend toward more vagrants is real.
To read about banding studies that showed the difference in migration routes, see this paper by Royall:
http://elibrary.unm.edu/sora/Condor/files/issues/v073n01/p0100-p0106.pdf
The North Dakota surveys were published by Nelms et al. (1994) in Am. Midland Naturalist (I don't have a link for that).
Louis Bevier
Fairfield
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