Red squirrels living in the Yukon experience a significant amount of stress, even if they have plenty of food available. During times of high population growth, red squirrels breed earlier in the year and give birth to smaller litters that grow up faster.
Ben Dantzer at the University of Michigan and colleagues at the Kluane Red Squirrel Project wanted to learn what caused the females to speed up the growth of their offspring. To find out, they set up loudspeakers in a forest and blared the sounds of squirrel chatter. They wanted the females to believe that the red squirrel population was booming in the area and see how they would respond.
Females who gave birth after hearing the broadcasted squirrel chatter had offspring that grew faster than babies born to females in a control group. The researchers found that the differences did not depend on the amount of food available.
The researchers analyzed the mothers’ fecal matter and found that those with faster-growing babies had higher than normal levels of the stress hormone glucocorticoid. This hormone drove the offspring’s rapid growth, which increased their chances of survival.
Dantzer and the other researchers want to find out if the young squirrels’ rapid growth was due only to hormone levels prior to birth or if it was also influenced by the mothers’ behavior. They are developing radio collars with cameras that they plan to use to study nesting activities, such as nursing and licking, which affect growth rates.
After they finish developing the collars, the team plans to repeat the experiment with the loudspeakers and follow the offspring that are born afterward throughout their lifetimes, which can last up to eight years. The want to learn what effect rapid growth has on the aging process. They hope that by studying how wild animals respond to stress and environmental challenges, they might be able to gain insight into how to treat medical problems related to stress in humans.