Why vultures matter -- and what we lose if they're gone

http://www.eurekalert.org/pub_releases/2016-05/uou-wvm050516.php

Public Release: 5-May-2016
Why vultures matter -- and what we lose if they're gone
University of Utah researchers highlight ecosystem and human impacts of vulture declines
University of Utah

vultures in some parts of the world are in danger of disappearing. And according to a new report from University of Utah biologists, such a loss would have serious consequences for ecosystems and human populations alike.

The primary threat to vultures, according to the report published today in Biological Conservation, is the presence of toxins in the carrion they consume. On many continents, vultures are the unfortunate victims of poisoned carcasses -- especially impactful because dozens -- or even hundreds -- of vultures can feast on a single carcass. Populations of most vulture species around the world are now either declining or on the brink of extinction.

Losses of vultures can allow other scavengers to flourish, according to biologists Evan Buechley and Ça?an ?ekercio?lu. Proliferation of such scavengers could bring bacteria and viruses from carcasses into human cities.

•••••

In the mid-1990s India experienced a precipitous vulture decline, with more than 95 percent of vultures disappearing by the early 2000s. "That was a massive collapse that led a lot of people to really focus more attention on vultures," Buechley says. The cause was eventually traced to diclofenac, a veterinary anti-inflammatory drug that relieved pain in cattle, but proved highly toxic to vultures. Hundreds of vultures would flock to each cattle carcass. And if the cow had recently been treated with diclofenac, hundreds of vultures would die. Because of this highly gregarious feeding behavior, less than one percent of cattle carcasses contaminated with diclofenac could account for the steep vulture decline. Fortunately, international cooperation led to a total ban on veterinary diclofenac use. Buechley says the numbers of vultures have stabilized, and are now showing signs of slowly increasing.

Now, the center of the vulture crisis is in sub-Saharan Africa. "In Africa, it's a lot more challenging," Buechley says. "It's a darker story." Potent newly affordable poisons are used to control predatory pests, such as lions or jackals. The poisons are so toxic that they can cascade through ecosystems: birds, mammals and insects are often found littering the area around these poisoned carcasses. But, as the predominant scavenger, vultures take the brunt of the poisoning and face the largest number of casualties. For example, an elephant carcass poisoned in Namibia in 2007 killed as many as 600 vultures. In other cases, vultures are the victims of poachers who poison carcasses so that vultures do not give away the location of illegally taken animals. "Vultures are taking the hit, indirectly, for a lot of this human-wildlife conflict, as well as the illegal trade in animal parts," Buechley says. This crisis, unfortunately, is ongoing.

•••••

In vultures' absence, other scavenger populations increase to take advantage of all of the uneaten carrion. By some estimates, in Central America, South America and Africa, vultures eat more meat than all predators combined. Without vultures, animals that eat carrion as a part of their diet (called facultative scavengers, as opposed to vultures, which eat only carrion) proliferate to take advantage of the available nutrients in a dead carcass. "There are a ton of nutrients in carrion that are going to be taken advantage of by something," Buechley says.

Crows, rats, dogs -- any of these species can suddenly become abundant and dominant, to the point of crowding out the remaining vultures. Hundreds of vultures on a carcass can easily frighten away packs of dogs, ?ekercio?lu says. But when only a few vultures are left, the dogs can rule.

Such changes in populations of certain animal groups can upset the balance of food webs. "All these facultative scavengers are also predators, and so they also go out and eat other organisms too," Buechley says. "You have this cascading effect."

•••••