Of a Feather: The spread of the scavengers

By BILL CHAISSON
By Bill Chaisson

Turkeys are ubiquitous this time of year, with many females foraging on the roadsides with half-grown to nearly full-grown poults. We were driving back from Jaffrey on Route 114 last weekend, when we saw a lone turkey-sized bird slowly strutting along the roadside. When I gave it a second look, I could see that it was not a turkey, but the aptly-named turkey vulture.

Shorter legged than an actual turkey, the vulture is also a much darker shade of brown and lacks the band of chestnut at the tips of the tail feathers. But, of course, the two species share the mottled bare red skin that makes their heads look a little too small for their bodies. And while the turkey is the heaviest bird in North America, the turkey vulture is built for the air and weighs next to nothing.

Vultures are scavengers. They have weak talons, and their beaks are not hooked like those of the raptors. Instead their adaptations are for finding and dining on carcasses. Featherlessness is an obvious advantage for a bird that spends a certain amount of time with its head shoved into decaying flesh. Less obvious are the physiological features that help it find a meal.

The turkey vulture (Cathartes aura) is able to stay in the air for hours without flapping its wings. Although they are between two and three feet long and have a 6-foot wingspan, they weigh a little more than 3 pounds. A bald eagle, which has an 8-foot wingspan, weighs two to three times as much. Vultures survey the ground from hundreds of feet in the air in groups called “kettles.” You may be able to see only a few birds from below, but many more birds can see each other. When one locates a carcass and drops down to investigate, all the rest follow. Consequently, you may have seen only two or three in the air, but suddenly a dozen will land next to their next meal.

Many vulture species find their food with keen eyesight, but the turkey vulture adds an uncanny sense of smell. They are able to detect carrion from a mile away and have the largest olfactory apparatus of any bird. Vultures are reluctant to leave a carcass once they have found it, which provides the best opportunity to get a good look at them. Up close appear to have one large opening in the middle of their upper mandible, protected by a bony ridge. This structure protects their nostrils while they are feeding.

Allan R. Keith and Robert P. Fox’s “Birds of New Hampshire” was published in 2013. They document only three records of C. aura in New Hampshire before 1900 — the first one at Hampton Falls in 1882 — and only two more by 1940. Through 1950 there are no records north of Merrimack, Cheshire and Rockingham counties. Since that time the species has been spreading up the Connecticut and Merrimack river valleys. Birds began to be seen throughout the summer in the 1960s, but breeding was not confirmed until 1981 in Antrim and Lebanon. Breeding bird surveys show it increasing in the state by 11% per year since 1966.

As a kid, I had a list of Dutchess County birds from the Waterman Bird Club. Next to the name of each species were its dates of arrival and departure. Most showed up in the spring and departed in the fall, although a few, like the tree sparrow and the rough-legged hawk, were on the opposite schedule. After a winter of watching the same 10 species (or less) at my bird feeder, I was always ready for spring. The blackbirds arrived in late February, but the turkey vulture was right behind them, making its way up to the mid-Hudson Valley by March.

In the southern parts of their extensive range — they are found clear down to Tierra del Fuego — C. aura is a permanent resident. What causes them to withdraw from the northern third of their distribution in North America? In a word, the cold. While vultures do not have impressively hooked beaks, their bills are strong, but they can’t tear apart a frozen carcass.

The other North American member of the family Catharidae is the black vulture. Overall, it has a more southern distribution than the turkey vulture and is generally less common throughout the United States, drawing even in numbers in Mexico and through the Caribbean. It is not particularly closely related to the turkey vulture. Coragyps atratus is smaller, more compactly built, with shorter, broader wings and a short tail.

The turkey vulture holds its wings in a dihedral position (slightly above horizontal). The black vulture holds them horizontally, but does not soar as efficiently, frequently resorting to flapping. While the chocolate-brown turkey vulture appears black, C. atratus really is black all over, including the skin of its bare head.

There are only scattered records of black vultures in New Hampshire before 1992, when one was spotted at Boscawen in April. Before 2013 all records were only for dates outside the breeding season; these were wandering birds. Throughout their range black vultures tend to be permanent residents, migrating only a short distance or down from higher latitudes in the winter. A look at the NHBirds online forum, however, reveals that black vultures are now being spotted during the summer in New Hampshire. This year birds were seen near Hinsdale and Portsmouth in June. One was seen on July 15 at Westmoreland.

The most prevalent theory for what is causing the spread of vultures focuses on the nature of development. Suburban sprawl works in favor of carrion eaters because it multiplies miles of road faster than it increases the density of the human population. More roads mean more roadkill and more for vultures to eat. As winters warm, they may be residents here through all four seasons.

Bill Chaisson, who has been a birdwatcher since age 11, is a former editor of the Eagle Times. He now works for the Town of Wilmot and lives in Sutton.