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France’s native brown bears, Ursus arctos, need more women. That’s the conclusion of a group of scientists studying the nation’s two remaining populations of the bears, which are on the verge of extinction.

Both are found in the Pyrénées mountains.

One, the central sub-population is doing fairly well. It was created by moving brown bears there to start a new population. But the native bear population, slightly to the West, is in decline.

The causes, say researchers, could be a result of the skewed sex ratios of the groups. The central bear population has more females than males. The western group has more males than females. The researchers looked at field data from 1993 to 2005 and found that the Western bears produced healthy cubs at a lower rate than the centrally sited bears. Their research is being published today in the journal PLoS ONE.

Too many male bears can be a problem. When there aren’t enough females to go around, males resort to killing cubs, so that the cub’s mother becomes reproductively available again. That might be a good reproductive strategy for the individual bear, but it’s a bad one for the population as a whole.

The answer, the researchers say, is to bring new female bears into the area to even out the sex ratio and stop the male bears from killing cubs.

"Our results suggest that having a viable bear population in France requires further translocations. In particular, male bears need more females," says one of the study’s authors, Guillaume Chapron from the Grimsö Wildlife Research Station, Swedish University of Agricultural Sciences, Sweden. He worked with colleagues from Washington State University and the Office National de la Chasse et de la Faune Sauvage, France.