Signs of Spring 5: Turkey Vultures!

Photo by D. Sillman

(Click here to listen to an audio version of this blog!)

Almost every evening for the past two weeks Deborah and I have watched a flock of vultures circling over the trees just to the north and west of our house. Most nights there are only four or five birds in the flock, but one night there were over a dozen. Occasionally, one or two of the birds glide into the large silver maple tree at the northwest corner of my field. They land in the branches, flutter their wings to stabilize themselves, and then stay a couple of minutes before taking off again to re-join their companions in their steady circling around the area. A few nights ago, though, at least ten of the vultures landed in the silver maple and settled in for the night.

A flock of circling vultures (called a “kettle”) is an omen of great literary power. It foretells death or impending disaster or doom. Just the image we need while we are isolating in place away from the coronavirus! Actually, vultures are the biological cleanup crew for our ecosystems! We should all thank them for all of the carcasses they dispose of!

Some neat names associated with vultures: vultures just hanging around (on the ground or on tree perches) are called a “committee,” and vultures group feeding at a carcass (which apparently they do with great manners and social skills (see below)) are called a “wake.”

I wrote a blog about vultures back in 2014. Here is an update!

Photo by Dori Wikimedia Commons

The turkey vulture (Cathartes aura) 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 (they weigh up to four pounds and have wing spans up to six feet) and 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 wobble just a bit (and are held in an upward “V” (for vulture?) shape) as they soar in great circles in the updrafts.

Turkey vultures are found all across southern Canada, the continental United States, Mexico, Central America, and down South America 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, each day along their migration routes they must seek out secluded roosts as evening approaches.

Hinckley, Ohio (a small town just south of Cleveland) celebrates the spring return of their turkey vultures with a “Return of the Buzzard” day on March 15. For the past fifty-seven years they have been greeting the returning flocks of turkey vultures as an important sign of spring. It makes more sense than Groundhog Day, that’s for sure (although it less aesthetically pleasing than House Cat Day!).

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. Actively foraging and flying turkey vultures assemble in great flocks that can rise together in circular paths in the thermals of the heated atmosphere.

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 M. Baird 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, are possible threats to 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 beak. They also show a distinct preference for relatively fresh kills and will not readily consume rotting carcasses.

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 laid 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 breeding 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!