Photo by M. Baird Wikimedia Commons
(Click on this link to listen to an audio version of this blog … Vultures of Colorado
There are three species of vultures found in the United States: the turkey vulture, the California condor and the black vulture. The turkey vulture (Cathartes aura), though, is the only vulture currently found in Colorado. The California condor (Gymnogyps californianus) probably once flew over Colorado’s mountains and plains, but the extinction of the great herds of grazing animals in the Late Pleistocene and, probably, direct human hunting drove them into their current, limited West Coast range long ago (see Signs of Winter 3, December 17, 2020). Black vultures (Coragyps atratus) are primarily found in the southeastern United States (I remember seeing flocks of them up close in their winter, nesting caves in the Texas caprock back in the early 1970’s), but they may be expanding their range northward (see discussion at the end of this blog!).
The turkey vulture is a very common sight in our Colorado skies. It is a bird that everyone knows and almost no one loves. They are a joy to watch soaring along in their great circles across the sky, but the closer you get to them the less majestic they seem! They are large birds weighing up to four pounds with wing spans up to six feet, and they are the most abundant and most widely distributed avian scavenger in the New World. They are easily recognized on the ground by their featherless, red heads and in the air because of their broad, “eagle-sized” wings that characteristically held upright in a “V” (for vulture!) and wobble just a bit as the birds soar in the updrafts.
Turkey vultures are found all across southern Canada, the continental United States, Mexico, Central America and down South America all the way to Tierra del Fuego. Birds in the northern regions of this broad distribution migrate to warmer habitats in the winter while birds in the warmer to milder regions of this range stay in place all year round. The vultures in the northeastern United States tend to migrate to Florida or Texas, while birds in the northwestern United States migrate all the way down to South America possibly as far as Argentina. Migrating flocks can be extremely large (thousands of individuals!). Turkey vultures, though, cannot fly at night (they require the thermal updrafts generated by the heat of the day) and, so, at the end of each day along their migration routes they must seek out secluded, night roosts.
The seasonal migrations of turkey vultures is celebrated all across the country! Hinckley, Ohio (a small town just south of Cleveland) marks the spring return of their turkey vultures with a “Return of the Buzzard” day on March 15. Makanda, Illinois celebrates the southward, Fall migration of their turkey vultures with a “Vulture Fest” on the third weekend of October, as do the vulture aficionados in the Kern River Valley of California with their September “Autumn Nature and Vulture Festival.” Down in Georgia, at Reed Bingham State Park, thousands of over-wintering, migrating turkey vultures are welcomed in the later Fall to their roosts in the pine and cypress trees of the park.
Photo by P. Tryjanowiki, Wikimedia Commons
There is even a international “Vulture Awareness Day!” (The first Saturday in September!). Vultures get lots of attention (but still not very much love!).
The turkey vulture is an extremely gregarious bird. They roost in large, communal groups in specific locations that may be used for many generations. During the day, smaller, foraging groups of turkey vultures may pause in the high branches of a tree or on the roof of an abandoned building forming a group called a “wake.” Actively foraging and flying turkey vultures assemble in great flocks that can rise together in circular paths in the thermals of the heated atmosphere. These swirling flocks are called “kettles” because of their resemblance to heated water boiling up in pan.
Turkey vultures are very long-lived birds. Life spans up to 25 years have been recorded. They have few predators except for a “usual suspects” list of potential nest predators (raccoons, skunks, foxes, opossums, snakes, etc.). They are relatively timid birds who will, if challenged at a carcass by another scavenger (like an eagle or a black vulture), regurgitate their ingested materials for the challenger to consume. At a carcass, turkey vultures feed in an organized, individual manner. Turkey vultures waiting for their turn at the carcass are exhibiting a behavior called “queuing.” Turkey vultures respond to threats and danger primarily by vomiting on the source of the danger. Since their stomach contents are typically acidic slurries of dead animal flesh, this behavior is quite an effective deterrent against aggression.
Photo by Shravans14, Wikimedia Commons
The impact of DDT on egg shell stability reduced the turkey vulture population slightly, but the banning of this pesticide has led to a completely recovered and, possibly, growing worldwide population. Potential lethal impacts of lead ingestion (from bullets and pellets in hunter-killed animals), though, is a significant danger for turkey vultures. Turkey vultures have also been killed by farmers and ranchers out of concern that these carrion consuming birds will spread pathogens and diseases from carcass to carcass. The great efficiency of the turkey vulture’s digestive system, though, very effectively destroys ingested pathogens (turkey vulture fecal materials are completely free of any pathogenic organisms).
Turkey vultures use their extremely well developed sense of smell to locate a carcass. This is most unusual since most avian scavengers and birds of prey utilize vision to find their food. This reliance on scent detection explains why foraging turkey vultures soar at lower altitudes than other types of vultures, and it may also explain their “wobbling” behaviors in flight (this motion may increase their ability to detect and precisely locate a scent source). Use of scent also enables turkey vultures to find buried or cached carcasses that had been hidden by some terrestrial carnivore. The greater abundance of turkey vultures in open or semi-open landscapes is also probably related to their particular method of finding food. Highways all over North and South America have become prime foraging habitats for this species.
Turkey vultures have extremely weak feet and blunt talons. Thus, they are not able to readily kill prey or rip at a carcass with anything other than their sharp, curved beaks. They also show a distinct preference for relatively fresh kills and will not readily consume rotting carcasses.
Public Domain
Turkey vultures mate for life, but upon the death of a partner an individual may take a new mate. Courtship behaviors include a “dance” involving raised wings and feet and long, following flights led by the male. Nests are located in individually selected locations not far from the pair’s communal roost. The term “nest” might actually be a bit of an exaggeration in describing the egg site for a turkey vulture. It is typically a site located on the ground (in a cave, hollow log or tree stump, or in a dense mass of vegetation) where soil and leaf litter and pieces of rotting wood have been pushed aside to make a spot for the one to three eggs. In a given area there will be relatively few specific locations that will suitable for a turkey vulture to build its nest. A chosen site, though, may be used for a decade or more. Both parents incubate the eggs and also the nestlings. Both parents feed the rapidly growing young. Incubation time is between 28 and 40 days, and nestling developments times are between 60 and 84 days. So, at a maximum, a reproducing pair of turkey vultures may spend over four months in intense caring for and rearing of their young.
Turkey vultures are not beautiful to look at, they make no beautiful songs (in fact they lack the organ of song generation (the syrinx) completely!), they eat dead animals, they smell bad, and if you get too close to one it will vomit on you (did I mention that they don’t make very good pets?). They are, though, beautifully adapted to their scavenger role in our ecosystems and have many good if not noble traits. They form lasting social and mating bonds, they are very good parents, and they have excellent “table” manners at a carcass!
Black vulture, Photo by Rangerbob13, Wikimedia Commons
There was an article a month or so ago in The New York Times about black vultures. Black vultures, as I mentioned above, are found in the southeastern U.S. They are starting to move northward, however, possibly because of the increasingly mild winters in the northern states. Flocks of black vultures were observed in Indiana where, according to a number of eye-witness reports, they were seen killing new-born cattle. Some of the attacked calves seem to have health problems ranging from scours (an intestinal illness) to broken legs, but some may have been healthy animals. This apparent transition of a scavenger into the role of a predator raises both alarm (especially in the minds of the cattle farmers) and also some doubt (in the minds of most ornithologists). This might be, though, a most unexpected consequence of the ongoing warming of our planet.