The European squirrel Sciurus vulgaris plans its children according to the future food supply. Photo: Gianfranco Scieghi
Reading Squirrel can predict how many seeds a tree will carry in the coming season and plan the number of their children according to the future food supply. With this strategy they win in an evolutionary tug-of-war against spruce and pine trees, which actually wanted to trick the squirrels with periodically changing seed production. Squirrels are the enemies of the spruces. They eat their seeds, minimizing the reproductive success of the conifers. Therefore, the trees have developed a counter-strategy: every few years, they produce a particularly large amount of seeds, in the years in between there are less. They outsmart their predators, because animals can only reproduce if there is enough food for them and their offspring. During the years of famine, the trees keep the number of seed-eaters to a minimum, so that enough seeds remain for their reproduction during the one-off surplus production.

However, the squirrels often thwart these plans, as Boutin and his colleagues have now discovered. For more than twenty years scientists in Canada, Italy and Belgium watched the game between squirrels and their fodder trees and discovered the unexpected: somehow the red rodents can foresee the next big harvest and produce more offspring in time for the lush feast this coming autumn. On the other hand, it would not make sense for the children to receive the next year as an answer to the boom, because then there would not be enough to eat for parents and offspring again, the researchers explain.

"It's as if the squirrels are pursuing a very successful strategy on the stock market, " Boutin compares. "While it still looks bad in the market, they are investing a lot, their own offspring, but they are paying high dividends when the market is rising again."

The scientists can only speculate on the question of how the animals already know in advance how much food to expect. However, they suspect that the squirrels can detect the expected harvest through the buds of the trees they eat in the summer. display

The American squirrels, also known as red squirrel, have also mastered an additional challenge, as the biologists discovered: they throw like the European squirrels a second time a year and were already pregnant when they still nursed the previously born. They have also overcome a physiological hurdle, explain the researchers, because usually prevents suckling the conception of other children.

Stan Boutin (University of Alberta, Edmonton) et al .: Science, Vol. 314, p. 1928 ddp / Annette Schneider


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