Stressed Hatchlings Become Obese Adult Birds, Researchers Say

Stress can have a long-lasting effects on baby birds, according to Newcastle University researchers, who found that chicks who have a harder time feeding as newborns are more likely to be fatter and greedier than their more fortunate siblings later in life.

"Building up body fat reserves as a safeguard against times of potential future famine is an evolved survival mechanism. What we have shown is that birds that had struggled against larger brothers or sisters for food early on were keener on finding food and tended to overeat when they became adults," Dr. Clare Andrews, one of the study researchers from the Newcastle University Centre for Behaviour and Evolution, explained in a news release.

This behavior in birds is similar to obesity trends observed in humans, researchers added. People tend to eat more food during a single sitting if they are unsure when their next meal may come.

For their study, researchers tested the disadvantages some European starling birds face when experiencing increased competition for food at a young age. When a group of smaller starlings were placed among larger hatchlings the smaller ones had to work harder – and subsequently exhausted more energy – when trying to get their parent's attention or move to the best feeding spots. On the other hand, similar-sized chicks placed in each other's company lived in relative luxury.

To test how early feeding stress affected individual starlings later in life, researchers presented the same birds with the choice of either feeding on easily accessible sources of crumbs or on hidden crumbs that took more time and energy to acquire. Researchers concluded that "hungry" starlings, or those at a disadvantage, had an embedded memory that made them fearful of being hungry. As a result, they spent more time searching for hidden crumbs and ate the freely available crumbs only after exhausting other food resources.

"By carrying extra energy reserves as body fat, or knowing where else to find food if need be, birds growing up in more difficult conditions might be insuring themselves against starvation in case of future food shortages," Melissa Bateson, a professor of ethology at Newcastle University and one of the study researchers, added.

The study was recently published in the journal Animal Behaviour.

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