Tree swallow study: Stressful events have long-term health impacts

Date:  August 28, 2018

Source:  Cornell University

Little is known about how brief yet acute stressors -- such as war, natural disasters and terror attacks -- affect those exposed to them, though human experience suggests they have long-term impacts.

Two recent studies of tree swallows uncover long-term consequences of such passing but major stressful events. Both studies provide information on how major stressful events have lasting effects and why some individuals are more susceptible to those impacts than others.

"We aren't looking at humans in either of these studies, but this research certainly could have implications for how humans respond to stress," said Maren Vitousek, assistant professor in the Department of Ecology and Evolutionary Biology. "The basic way that most vertebrates respond to stress is quite similar. We often see similar things predicting stress resilience in humans and in other animals."

The first study was published in Proceedings of the Royal Society B. Vitousek is the paper's first author.

The researchers developed a new method for manipulating hormone levels in free-living birds: They dissolved a stress hormone (glucocorticoid) in a gel and put it on eggs in tree swallow nests. The females, the only ones who incubate, absorbed the hormone through their skin. They were given five separate doses for an hour each early in their reproductive periods.

After absorbing the hormone, females fed their offspring at lower rates once they hatched, which led to much smaller offspring compared to two types of controls (one type with gel but no hormone on an egg and the other undisturbed). The smaller offspring in turn had lower survival rates.

"The take-home message here is that the hormones that birds would be exposed to if they had a short-term stressor do have these long-term effects," Vitousek said.

The researchers also found that birds exposed to higher doses of glucocorticoid were more likely to endure lingering impacts, she said. This result suggests that individuals who naturally mount a stronger hormonal response to brief challenges may be at greater risk of suffering from lingering effects of stress, Vitousek said.

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