Protracted Custody

A Scandinavian brown bear female and her cubs

Sigfried Klaus

The survival of a heavily hunted species should select for fast reproduction and accelerated life histories. But when hunting regulations protect female reproductive status, other patterns of selectivity may evolve. In a recent study of female Scandinavian brown bears, Ursus arctos arctos, from a heavily hunted population in south-central Sweden, it appears that hunting management practices have changed female reproductive behavior in a relatively short time.

Ecologist Joanie Van de Walle from the Université de Sherbrooke, Québec, Canada, and a team of researchers evaluated over twenty years of detailed data that documented the birth, reproductive success, and death of 200 individual female bears as part of the Scandinavian Brown Bear Research Project. They found that before 2005 most females kept their cubs with them for one and a half years, while only 7 percent cared for their cubs for two and a half years. However, by 2015, the proportion of females that kept their cubs for two and half years rose to 36 percent.

The authors hypothesize that this trend is a result of regulations enacted in 1986 that prohibit hunting of female bears with dependent cubs of any age, not just their young born that year. Mothers that kept their cubs longer had a greater survival rate, as “females that are alone during the hunting season are four times more likely to be killed,” says Van de Walle. Thus, in a twist on usual child-rearing practices, when a mother allows her cubs to stay an extra year, they end up protecting her.

Longer cub-rearing also had a cost, however, as these same mothers reproduced less frequently. The research team expected that this decrease in reproduction would lower the population growth rate over time. Instead, they found that the two effects—increased survival but reduced reproduction—appeared to nullify one another, resulting in a growth rate similar to what they would expect had there been no trend toward longer maternal care.

Still, the Scandinavian brown bear population may be affected in other ways. A larger proportion of the population could end up being composed of reproductive females, therefore increasing the vulnerability of solitary females and males to hunting. These potential changes in population dynamics may be unexpected and unintended, says Van de Walle, but adds, “It’s important to understand them in order to adapt management decisions.” (Nature Communications)