Filthy, Stinking Niche: Vultures in the Ecosystem

Vultures have garnered perhaps the worst reputation of all birds worldwide. They’ve been blamed for killing cattle and stalking vulnerable prey.  And while they do scavenge upon what humans would label as filthy, gross meals, without the tidy housekeeping of vultures, any ecosystem would quickly be overrun by insects and diseases.

Photo: Rhonda Spencer

If being maligned in popular culture wasn’t enough insult, vultures are also generally ignored by even the most ardent wildlife watchers. Such is the fate of many common creatures, like rabbits and sparrows, whose only offense is being commonplace. However, let’s not be hoodwinked by the mundane, and shine a spotlight on these underappreciated “Queens of Refuse” and their redeeming qualities.

Vultures don’t kill. They instead scavenge on dead animals. Cars, diseases, and predation cause animal deaths in the Sonoran Desert and vultures are among the most prompt in the ecosystem cleanup crew. Because they don’t have much vertebrate competition for roadkill, they effectively dominate a specialized niche. A freshly dead carcass can be quickly overrun with microbes, fly larvae, beetle larvae, and fungi. Carrion can host salmonella, anthrax, rabies and botulism. Without vultures to rapidly consume a dead animal to the bone, these diseases would linger in the environment and spread throughout animal populations. Vultures can handle and eviscerate deadly diseases due to their incredibly strong stomach acid and can therefore digest rotting flesh and bacteria without getting sick. Just imagine if we didn’t have these carrion custodians in our desert.

Photo: Robert Henderlong

Vultures aren’t usually considered cute. They lack the large eyes of mammalian babies and their bald heads aren’t as endearing as the iridescent, feather-covered heads of hummingbirds. However, bare domes are a twofold adaptation: to radiate excess heat off their head (it’s a means of thermoregulation in a hot, arid environment) and to keep dead flesh and excrement from soiling their feathers. Without a substrate to cling to, putrid organ meat does not last long on a vulture.

Spindly legs on the opposite end of the bird make one well aware that the avian lineage isn’t all that far removed from dinosaurs, evolutionarily speaking. The scaly pink legs are often depicted as white as they are frequently covered in hardened uric acid. By peeing on themselves, vultures stay cool. (Swamp cooling is used by more than just humans in the arid southwest!) The uric acid has the added benefit of killing diseases that hitchhiked onto the birds and off of roadkill. Sanitation via urination! Their legs end in a flat-footed design. Although these animals can (and do) perch, they are more often standing on the ground and need those fallen arches to help balance. They do have a comical and distinctly awkward ambulation, but it gives them a leg up in life.

The Sonoran Desert is home to both turkey and black vultures and the two species are often seen together in a desert vista. While observing a kettle (a group of vultures spiraling in flight), look for a few key differences between the two. Turkey vultures have red heads, long black and white wings, hold their wings in a “v” shape, and rock unsteadily while soaring. Black vultures have an all-black head, black wings with white just at the tips, and hold their wings flat while soaring.

Due to their keen sense of smell, turkey vultures are the first to come upon odor plumes and then circle to locate a dead animal. They are the first responders to a scene. It is interesting to note that these birds help humans locate leaks in natural gas lines, as natural gas has a distinct scent that attracts the birds. Black vultures need only watch the behavior of turkey vultures and follow them. At a carcass, black vultures are known to muscle their way in and bully turkey vultures away from the prey item. In some parts of the desert both species are then run off by the real menace- the caracara. The three species have an established, and very literal, pecking order.

Most articles highlighting animals share a sobering reminder: this animal is disappearing due to human activities. This pattern is true for Old World vultures as their populations are in a steep decline due to purposeful poisoning of large carnivores. In India, collapse of the vulture population in the 1990’s led to an explosion in the number of wild dogs, and a tremendous increase in rabies, causing a public health crisis. Scientists are concerned the same could potentially happen in West Africa.

Compared with the twenty-three vulture species worldwide, our turkey and black vulture populations are of least concern. Their populations in America are actually increasing due to human activities Urban sprawl, road construction, and an increase in number of drivers have directly impacted the amount of roadkill. Thus, vulture populations are not only growing in density, but are also expanding their range northward. The primary human threats to vultures are cars (they get hit while eating roadkill) or lead poisoning after eating an animal that contains spent ammunition.

These “Queens of Putrescence” proudly display their bald heads, urine-soaked legs and flesh-eating skills which, all in all, can be pretty cute- in their own bird way. They fulfill an unsung but essential role in our environment. Bow down to them, if you wish.

Written by Catherine Bartlett, ASDM Education Specialist

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