Squirrels save for the family’s future

Red squirrels about to start a family don’t exactly set aside nuts for college. Yet some females do hoard extra food to pass along to youngsters that have not yet been conceived.

A red squirrel in Canada defends its territory. T. Karels

In northern Canadian forests, the red squirrels, Tamiasciurus hudsonicus, survive winters thanks to caches of fir cones. The animals nip the cones off trees just before they open and bury their treasures in a pile of debris, or a midden. This heap forms the center of a territory that a squirrel defends fiercely.

In a long-term study, Stan Boutin of the University of Alberta in Edmonton and his colleagues allowed female squirrels a chance to take over a second, undefended midden. Among seven females who had raised young, six did stretch out their territories to include the spare midden. However, out of six females that had never raised a family, only one took over the extra midden.

That makes sense, Boutin argues, because the extra midden benefits not the mom but the young to whom the middens are bequeathed. In the Oct. 22 Proceedings of the Royal Society of London B, the researchers point out that females who have had litters once almost always have another the next season.

But females who haven’t yet had offspring remain less assured of parenthood next season. The mother squirrels did occasionally dip into their reserve midden as well as into their original one. Yet the two-midden females didn’t seem to fare particularly better than females living off a single midden, report the researchers.

Of the litters that survived to weaning, one youngster took over the spare midden. That windfall increased that particular little squirrel’s chances of surviving its first winter alone. Boutin emphasizes that the reserve midden came into the families’ possession a good 4 months before the youngsters’ mothers even mated. The squirrels’ midden takeovers represent the clearest example yet in a nonhuman of “anticipatory parental care,” he says.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.