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When Animals Worry

Chronic stress affects reproduction and survival levels

Sparrows, rabbits and other wild animals can suffer so much from the daily grind of finding food while avoiding predators that they can experience a form of chronic stress – and this can affect their reproduction and survival levels.

Researchers collected blood samples from 91 song sparrow fathers with six-day-old nestlings. They found food and predators together affected corticosterone levels (the principal stress hormone in birds), free fatty acid levels (the energy molecule used for flight), anemia, and nestling numbers and condition. The researchers concluded that birds in environments with limited food and many predators were the most stressed.

The study was conducted by Dr. Michael Clinchy and Professor Rudy Boonstra of the Centre for the Neurobiology of Stress and department of zoology at U of T’s Scarborough campus, and colleagues from the universities of Western Ontario, Washington and British Columbia.

In an earlier study on snowshoe hares, Boonstra and others showed that reducing predator pressure and boosting food levels led to an 11-fold increase in the population density of hares. In 2001, Professor Liana Zanette of the University of Western Ontario published the first study showing comparable effects in song sparrow reproduction.

“The fact that our new song sparrow data fit predictions from the snowshoe hare study so well suggests this is very general phenomenon,” says Boonstra. “If so, then targeting both food and predators may be the key in conserving threatened species.”

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