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In nature, survival of the fittest is key for newborns that are the most vulnerable to predators and for the red squirrels, the mothers know just how to give their offspring an upper hand. Squirrels that are bigger in nature tend to have higher chances of claiming territory that comes with foods, such as seeds from the trees. With the territorial boundaries, these squirrels would not have to worry as much about foraging for food and competing with others. According to a new research study, red squirrels know how to use stress instead of food as a way to promote the growth of their young ones.

"When population density is high, only the fastest-growing offspring survive," explained Andrew McAdam, the study's researcher who is from Canada's Guelph University. McAdam and his colleagues observed the red squirrels from the North American region in Yukon. They devised field experiments in which the experimenters exposed the squirrels to recordings of territorial squirrel vocalizations, also known as rattles. The experimenters wanted mother squirrels to believe that there were numerous contenders and fellow threats within the forest.

The researchers found that the rattles triggered the pregnant squirrels to produce a stress hormone known as cortisol, which caused their offspring to grow significantly faster after they were born. The higher cortisol levels almost benefited the ruts of a big litter that would have otherwise remained small and vulnerable.

"Despite the widespread perception that being stressed is bad, our study shows that high stress hormone levels in mothers can actually help their offspring," a postdoctoral researcher from the University of Cambridge, Ben Dantzer stated. Although these squirrels appeared to grow faster and thus, were generally bigger than other baby squirrels, the researchers found that the rate of growth was not necessarily good. They found that these squirrels also burned out faster, meaning that they peaked too early and died faster than other squirrels that might not have grown as fast.

This study provided insight into the possible beneficial effects of stress for animals. Previous studies have looked into the role of stress for humans, and researchers have repeatedly found that some levels of stress can be helpful for humans as well.

The study was published in the journal, Science.