Turkey vulture (Cathartes aura)
A soaring Turkey Vulture, its long wings held in a shallow V as it teeters from side to side over open terrain, is a majestic and familiar sight to many Montanans. Up close, when its naked head and wrinkly nape are visible, the bird is much less appealing. This atypical raptor uses its keen sense of smell to locate the carcasses of dead animals upon which it feeds. Aside from the other two species in the genus, C. burrovianus and C. melambrotus, which also use olfaction to find food, no other vulture is known to have this ability (Houston 1984). Turkey Vultures have the widest range of the seven species in the family Cathartidae, occurring from s. Canada and throughout the continental U.S. to the Greater Antilles, Central America, and South America. Each fall, more than two million of them pass over a migration watch site in Veracruz, Mexico, with counts of up to 300,000 birds on peak days (S. Hoffman, pers. comm.). The evolutionary relationships of cathartid vultures have been hotly debated. Some authorities believe they should be placed with storks in the order Ciconiiformes, whereas other workers group them with hawks and eagles in the order Falconiformes; the latter placement is favored by the AOU (2007).
Subspecies: C. a. meridionalis
Status and Occurrence: Uncommon to fairly common breeding resident in w. half of state and uncommon breeding resident and migrant in e. half of state. Arrives from late Mar to early Apr and leaves from late Sep to early Oct. Rare outside this period, with notable sightings by Denver Holt near Frenchtown, 9 Dec 1991; by John Ormiston at Hamilton, 21 Dec 1996; by Dennis Flath near Three Forks, 9 Feb 2005; and by Betty Anderson near Roundup, 4 Mar 1949. Few nests have been found in Montana, and little is known about the timing of nesting events in the state. Montana's first specimen was taken by R. S. Williams on Belt Cr. on 28 Jun 1889 (MCZ 186555). Cameron (1907: 259) mentions a bird shot by a rancher near Mizpah in Oct 1896 that apparently was not preserved as a specimen.
Habitat: Hunts over a variety of habitats, including pastures, shrublands, grasslands, and forests. Also soars along highways in search of road-killed animals. Roosts (often communally) in large trees and on rock outcrops and nests in recesses in cliffs, in tree hollows, on the ground beside fallen trees and beneath shrubs, and in abandoned buildings (Kirk and Mossman 1998, Houston et al. 2007).
Conservation: BBS data indicate a significant survey-wide increase in numbers of 2.2% per year from 1980 to 2007. Data for Montana are derived from inadequate sample sizes and suggest a nonsignificant decline of 1.7% per year during the same period. The global population estimate is 4.5 million birds (Rich et al. 2004).
Turkey Vultures are vulnerable to lead poisoning from ingesting bullet fragments in carrion and to eggshell thinning from DDT contamination (Wilbur 1978, Kirk and Mossman 1998). They occasionally are shot for alleged depredations on livestock, are commonly struck by vehicles when feeding on road kills, and have a propensity to collide with aircraft owing to their “disinclination to take evasive action” in flight (Kirk and Mossman 1998) .
Historical Notes: Saunders (1921) believed that Turkey Vultures had been abundant but became rare after Bison numbers were severely reduced toward the end of the 19th century. Direct reports from the 1800s give a mixed view of the species’ abundance. Cooper (1869a: 596) noted that they were “Occasionally seen through the Rocky Mountains, but not very common” in the summer of 1860, and Coues (1878) failed to see them along the 49th parallel during the summer of 1874. Thorne (1895: 214) believed them to be “rare” at Fort Keogh from 1888 to 1892, his only mention of them during this period being “Twelve seen in June, 1889.” Hayden (1862: 151) stated that they were “Very abundant throughout the Northwest,” and Grinnell (1876: 83) considered them to be “Abundant on the plains” in 1875. In the summer of 1873, Allen (1874: 65) saw “Quite a number…assembled around Camp Thorne [Glendive], attracted, doubtless, by the offal from the beeves slaughtered for the support of the garrison stationed there.” Richmond and Knowlton (1894: 302) said they were “common” in Gallatin Co. in the summers of 1888 and 1890.
The most interesting historical accounts of the species in Montana are by Charles McChesney and Ewen Cameron, both of whom related second-hand reports of nesting “colonies.” McChesney (1879: 2392) reported that in the summer of 1878, Colonel Brackett “saw a large colony of them on a point on the Yellowstone, where they had evidently been breeding, as the tops of the trees were worn, and seemed almost bare of foliage on account of the number of these birds that had been roosting, resting, and flying about among them.” A rancher on the Powder R. named Dan Bowman told Cameron (1907: 259) that in the fall of 1883 vultures were “incredibly numerous in eastern Montana, and roosted in the thousands on the Powder River.” Bowman further stated that “The birds constructed their nests in the cottonwood trees along the river, the stench from these rookeries being so great that it was almost impossible to approach.” Cameron remarked that “Without doubt it was the prodigious slaughter of bison which attracted the birds, for while the southern herd…had already ceased to exist, the northern herd…was wiped out in 1883.” By 1906, Cameron considered Turkey Vultures to be “accidental wanderers” in the eastern part of the state with which he was familiar.
The notion that Turkey Vultures build nests in trees, a phenomenon that was not witnessed by McChesney or Cameron, requires an explanation because New World vultures do not build nests in the traditional sense. Bendire (1892: 163) relates a second-hand account of a Turkey Vulture nesting in an old heron nest in Texas. It is thus possible that the vultures seen by Brackett and Bowman roosted communally and also nested, albeit in smaller numbers, in Great Blue Heron colonies along the Yellowstone and Powder rivers, respectively. We suggest that in times of superabundant food, as would exist during the slaughter of large numbers of Bison, vultures would nest in unusual situations like old heron nests in trees, especially if more typical nesting sites were in short supply.
Contemporary Work: The species is virtually unstudied in the state. Systematic counts of migrating raptors conducted by HawkWatch International in the Bridger Mts. during fall yielded totals of no more than two Turkey Vultures per season from 1999 to 2007.
In recent years Canadian researchers have marked Turkey Vultures that nest in abandoned houses in Saskatchewan. An adult tagged with a satellite transmitter on 19 Jun 2005 initiated southward migration on 29 Sep, entered Montana airspace on 5 Oct, and remained in Valley Co. until 12 Oct, when it departed the state to the southeast (S. Houston, pers. comm.). A nestling marked with a wing tag on 6 Aug 2005 was seen in McCone Co. south of Wolf Point in mid-May 2006 (S. Houston, pers. comm.).
Sponsored by Stuart Houston, Saskatoon, Saskatchewan
Copyright Notice: © 2008. Jeffrey S. Marks. All Rights Reserved