Spring has sprung. Guelph is green, lush, and as usual full of squirrels. The University of Guelph campus is a prime place to spot squirrel pups following close behind their mother’s feet in a high-stress and very busy environment.
Andrew McAdam, Amy Newman, and Ben Dantzer of Guelph’s Department of Integrative Biology have recently published a study on how mother red squirrels raise their pups in stressful situations. Pups born into a hectic environment are much more likely to be nurtured by an extra zealous mother. When these babies leave their nest, or drey, they will be significantly larger than squirrel babies born in low-stress environments.
You can see a number of dreys around the city of Guelph and on campus – vaguely spherical jumbles of branches and leaves usually built quite high up in a tree.
McAdam, Newman, and Dantzer found that mother squirrels listen to the social cues of other squirrels. When stress factors increase, other squirrels make territorial defense calls, or “rattles.” The mother’s stress hormone levels increase in response to these noises, and she tailors the intensity of her pup-rearing accordingly.
A high population of squirrels is a stress factor. If the mother hears frequent territorial and defense “rattles” due to an exponential increase in the squirrel population, she knows her offspring must be fit and competitive.
The researchers employed some very clever means of manipulating the environment around mother squirrels. Newman and Dantzer played recorded squirrels calls in the forest they were studying and tricked mother squirrels into believing that they had more neighbours than they really did.
McAdam noted that, “when there are lots of squirrels around, only the fastest-growing squirrels survive. When population density is low, all squirrels survive well, so how quickly they grow doesn’t matter.”
Dantzer and Newman also fed some mother squirrels peanut butter laced with stress hormones; those mothers also raised faster-growing pups than control females.
“Despite the widespread perception that being stressed is bad, our study shows that high stress hormone levels in mothers can actually help their offspring,” Dantzer suggested.
The researchers note that similar principles most likely apply to other animals, though it is unclear as to what extent this applies to human parenting.