Scavengers like raccoons can be picky eaters


Birds and mammals preferred to feed on the carcasses of herbivores

Usually, when you picture a picky eater, a raccoon doesn’t come to mind. But new research from the University of Georgia has shown that scavengers like raccoons and vultures can be picky about what they eat. The study sheds light on how nutrients can circulate through food webs.

When multiple types of carcasses became available, scavengers of birds and mammals chose those of herbivores, such as ducks and chickens, rather than carnivore carcasses.

A photo of a raccoon captured by the motion-controlled time-lapse cameras set up by the research team.

Miranda Butler-Valverde, lead investigator at the to learn, published in Food Webs, installed remote cameras at the heavily forested Savannah River site near Aiken, South Carolina. Then Butler-Valverde, a recent graduate of the Savannah River Ecology Laboratory and the Warnell School of Forestry and Natural Resources, placed bird carcasses of various trophic levels in the area.

Trophic levels refer to placement in the food chain. A food web starts at trophic level 1 with primary producers such as plants. Herbivores are level 2 and carnivores are level 3 or higher.

A bobcat inspects the carcasses of two dead vultures, also thought to be scavengers.

A bobcat inspects two carcasses.

She placed 40 herbivore carcasses – 20 chickens and 20 mallards – along with the carcasses of 20 black vultures and 19 turkey vultures in the landscape

Motion-triggered time-lapse photos taken every five minutes for over a month showed scavengers, including coyotes, crows, bald eagles and wild boar, consuming the chicken and duck carcasses whole.

The cameras showed that there was less feeding on vulture carcasses. Scavengers, including coyotes and Virginia possums, consumed only 10 of the 39 vulture carcasses, five of each species. Some scavengers sampled or partially ate vulture carcasses.

The behavior of scavengers shows that animals may avoid disease

According to Butler-Valverde, now a wildlife technician at New Mexico’s Santa Fe National Forest, the fate of these carcasses sheds light on how nutrients can circulate through food webs.

A hawk thought to be a scavenger lands on the carcass of a bird next to railroad tracks

Cameras picked up a hawk eating from one of the carcasses.

“The vulture carcasses that were not eaten or only partially eaten were in the landscape for an extended period of time,” Butler-Valverde said. “This means that the microbial and invertebrate communities were likely able to take advantage of the lower competition and lack of disturbance in these carcasses. After the carcasses decomposed, nutrients would most likely have been incorporated into the soil and plant communities near the carcasses.”

Insects and microbes often miss opportunities to access nutrients from carcasses when scavengers quickly arrive and consume the prey, according to the study.

A bald eagle, also known as an occasional scavenger, perches on a bird's carcass

A bald eagle inspects one of the carcasses used in the study.

In this case, although the vertebrates at the higher trophic level arrived at the buffet early and obtained nutrients from lower-level carcasses, since the majority of vulture carcasses remained in the landscape, ecosystem balance occurred in the food web as everyone came to eat something or someone .

From a human perspective, one might expect the scavengers to choose the tastier meal, but researchers believe there’s more than the scavengers’ palates or taste buds at play.

James Beasley, a professor at SREL and Warnell and a co-author of the study, said the scavengers could avoid disease risks.

“Scavengers are mostly predators and higher trophic level species, and by scavenging on similar species they may be more exposed to pathogens that they may be susceptible to,” Beasley said. “So carnivores may be less likely or unwilling to eat other carnivores to reduce their exposure to pathogens.”

The study reports that what these animals ate while they were alive may have influenced the scavengers’ decision to eat them or not. Chickens and mallards are herbivores. Vultures feed primarily on the carcasses of dead animals, so the nutritional values ​​of carcass types differ.

Camera images show that cannibalism has occurred. Turkey vultures fed on vulture carcasses, but the study finds that most of these scavengers were immature, like toddlers who have yet to learn what is appropriate to eat.

Coyotes were the most common scavengers, followed by Virginia possums. Coyotes have eaten all types of carcasses, but have frequently visited vulture carcasses which they have not eaten. Butler-Valverde acknowledges that this behavior may be due to a scavenger not being hungry at the time, assessing the situation for a later return, and being wary of nearby predators.

The team’s research supports previous findings that fewer vertebrate species feed on carrion at higher trophic levels, but Butler-Valverde emphasized that feeding ecology is a relatively understudied area of ​​research. She said researchers should continue studying the ranges of the two vulture species to determine scavenging patterns and impacts.

Travis L. DeVault, Associate Director and Senior Research Scientist at SREL and Associate Professor at Warnell School, is also a co-author of the study.


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