Savvy squirrels outwit trees

Like good stock brokers, red squirrels predict when the market will be flooded with seeds and then invest big by producing a second litter of young, a new study finds.

"Lots of animals time their reproduction to match predictable increases in resources like the new growth of plants every spring," said lead researcher Stan Boutin of the University of Alberta. "But the interesting twist here is that these squirrels have figured out a way to produce this second litter of babies at a time when they have little food and before an ‘unpredictable’ boom in seed production.”

The results are detailed in the Dec. 22 issue of the journal Science.

Smart squirrels
Boutin and his colleagues monitored two species of red squirrels, including a natural population of American red squirrels in southwestern Yukon, Canada from 1987 to 2004, and Eurasian red squirrels in Belgium and Italy.

Somehow the squirrels could anticipate when the trees would be laden with cones, and only during these years they produced a second litter of young.

In addition to predicting the future, the squirrels were able to reproduce while females were breast-feeding the first litter — something that doesn't normally occur in mammals, said study team member Andrew McAdam of Michigan State University.

While the researchers still aren’t certain how the squirrels can predict the cone market from year to year, they think it might be some chemical or visual cue from the buds that ultimately form tree cones. Every summer the squirrels nibble on these buds. "Squirrels could be using a visual cue or a hormonal cue they gain from eating the buds," Boutin said.