Imagine estimating baby food availability and then planning kids. That’s what red squirrels in the Canadian Yukon and Europe seem to be doing, looking up spruce trees carefully, mentally calculating the seed cones to come and then deciding to have a litter or two.

Researchers report that squirrels are able to predict when the trees will provide such copious amounts of food and produce two litters one after the other just at the right time to take advantage of it.

Many trees produce relatively little seed in most years, which helps keep the populations of seed-consuming animals down. In certain years, the trees produce large amounts of seed, an event known as masting. With the seed eaters’ numbers reduced, having so much seed ensures that more of it will not be eaten and will have the chance to grow.

It’s a “swamp and starve” strategy, says Stan Boutin of the University of Alberta, lead author of a study on the squirrels in the journal Science. Most years, the trees starve the animals, and then they swamp them with food. “The predators don’t have time to respond.”

But the squirrels are different, says Dr Boutin, who has studied them in the Yukon for two decades. They know in advance when a mast year will occur, and after they have a first litter, the mothers interrupt their weaning and conceive a second one. “The squirrels time it so they have the maximum number of members in the population right when they can take advantage of that seed,” Boutin explains. Having an abundance of seed cones is critical for the young squirrels’ survival because it helps them break into a highly territorial system. “It’s such a big win for these females to produce that second litter.”

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