Feeding Food to Wild Animals May Impact Their Risk of Disease

Feeding food to wild animals may just impact their risk of disease. Scientists have found that supplemental feeding of wildlife can actually increase the spread of some infectious diseases and decrease the spread of others.

Giving food to wild animals is becoming more and more common. As people move into previously undeveloped areas and wildlife habitat is lost to development or agriculture, wildlife ecology changes. Natural sources of food decrease and new sources appear, provided by people. Sometimes these sources are intentional, like backyard bird feeders or winter feeding stations for elk. However, sometimes they're accidental, like landfills or garbage cans.

"We knew of studies of supplemental feeding showing both increases and decreases in parasitism and disease, but no one had synthesized them," said Daniel Becker, one of the researchers, in a news release. "We wanted to know if there was an overall net tendency, and we wanted to know what could explain the different responses."

The researchers combined over 20 published studies of supplemental wildlife feeding and infectious disease in order to understand infection patterns. This also allowed them to create predictive models of pathogen transmission.

With pathogens like bacteria or viruses, food sources that attract large numbers of animals can encourage transmission, including transmission from one species to another. In addition, the researchers found that even when the food provided is very nutritious, in most cases it's not enough to overcome the exposure risk of being in the midst of a large group with frequent aggressive contacts over resources. In many cases, the food is not nutritious enough to help and can even impair animals' immune defenses. For example, when tourists in the Bahamas feed grapes to rock iguanas, the reptiles' overall condition is impaired and levels of infection by hookworms are higher.

"For intentional feed sources like bird feeders, we expect parasites like bacteria and viruses to increase, so spacing these resources apart can help reduce the high contact rates driving transmission," said Becker. "And cleaning feeders periodically can help limit the buildup of infectious stages in the environment that occurs when lots of animals become more sedentary."

The findings are published in the journal Ecology Letters.

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