Black vultures

Karen Bartomioli’s article in last week’s Journal, “Vultures cluster around school,†gave a thorough and balanced picture of the rapidly expanding population of black vultures in our region, which has become a source of concern at North Canaan Elementary School.

Perhaps all that remains to be said is that the growing presence of “BVs†in this area, usually mixed in with the more abundant and closely related “TVs†(turkey vultures), is almost certainly a result of steadily increasing average winter temperatures in America, which most scientists attribute in large degree to human activities.

During the past four decades, the average temperature in the lower 48 states during the month of January has risen by nearly by 5 degrees Fahrenheit. This is according to a new report just released by the National Audubon Society that documents the dramatic northward shift in the ranges of many North American birds over the same time period. (The report, “Birds and Climate Change: Ecological Disruption in Motion,†is available on the Audubon Web site audubon.org/birds/bacc.)

The statistics, which were gleaned from Christmas Bird Count data, are staggering. Fully 60 percent of 305 species that were studied have exhibited northward movement in their winter range, and the average range shift was 35 miles.

Among well- known birds in our region, the ranges of the purple finch and wild turkey have both shifted northward by more than 400 miles, the ring-billed gull by over 350 miles, and the pine siskin by nearly 300 miles. For these species which, like our black vultures, appear able to adapt to the changing climate, the prognosis may be positive, though where and when such birds are seen is clearly in flux.

The report highlights other species, particularly habitat specialists, that seem unable to adjust. For example, the range of the eastern meadowlark, a grassland bird, has actually moved southward 25 miles, at the same time its populations have declined by more than 70 percent.

The influx of black vultures has been remarkable. BVs were almost unheard of in the Northwest Corner a decade ago. I remember seeing my first pair in this area less than 10 years ago, scavenging on West Cornwall Road. Now flocks in excess of 25 birds occupy roosts in Sharon and elsewhere.

I’ve written before about how to tell BVs from TVs, but here’s a quick recap: Both are very large, dark and heavy-bodied birds, but the BV is slightly smaller and more compact. Its head is always charcoal or black, while the TV’s is typically reddish. (Beware young TVs, however, which have grayish heads.)

In flight, the differences are fairly easy to detect. TVs are long-winged and relatively long-tailed, and hold their wings in a pronounced dihedral (“V†shape), habitually rocking side to side. The wings are noticeably paler along the entire trailing edge.

BVs’ wings have a bow-shaped appearance and are held in a shallow dihedral. The tail is quite short, and the birds never rock side to side the way TVs do. There is a sharply demarcated, triangular white patch at the tip of each wing.

Fred Baumgarten is a naturalist and writer. He can be reached at fredb58@sbcglobal.net. His blog is at thatbirdblog.blogspot.com.