Social stress alters hormone levels in red-squirrel mothers and leads to faster-growing pups.

Credit: RYAN TAYLOR

In a 22-year study, Ben Dantzer, now at the University of Cambridge, UK, and his team found that, in densely populated red-squirrel (Tamiasciurus hudsonicus; pictured) communities, females that had faster-growing pups saw more of them survive their first winter. The researchers simulated crowded conditions by playing recordings of squirrels' territorial cries. Mothers living in dense groups or exposed to the cries had higher levels of breakdown products from the stress hormone cortisol in their faeces. Pups of squirrels that heard the recordings grew faster than pups of females that heard bird noises. Feeding pregnant squirrels cortisol also boosted the growth rate of their pups, by 41%.

Science http://dx.doi.org/10.1126/science.1235765 (2013)