© BJ Kirschhoffer/Polar Bears International
4/28/2015 5:55:37 PM
Love on the Sea Ice
It's that time of year again, when polar bears are on the lookout for mates. Despite decades of studying polar bears we only have very few (if any) well-documented observations of wild polar bear behavior over the course of an entire mating season. This is because the mating part of the polar bear's reproductive cycle takes place in the spring months, out on the sea ice, far from most people.
One of the unanswered questions regarding female polar bears is whether they are what we call polyestrous—that is, do they go into heat (estrous) several times during the mating season, or only once? And for how long?
To answer this and other similar questions, researchers piece together a picture from all the observations that exist of individual polar bears in the wild + what we know from studies of polar bear genetics + hormonal information from studies of polar bears in zoos + dissection of reproductive organs from dead polar bears. Based on this, female polar bears seem to be in heat (estrous) once a year, for about three weeks.
However, a new paper just came out, reporting an observation of mating polar bears in late June, which is about a month and a half later than what is seen as "normal" mating season for these bears. You can find the paper here. As you can see, the authors speculate that perhaps this particular female polar bear did actually go into estrous a second time this particular spring, perhaps because she had lost her previous cub sometime during the mating season that had happened in the months before. However, the female being in estrous isn't enough in itself to get her pregnant—studies indicate that polar bear male sperm production only occurs during the actual mating season.
The specifics of the female polar bear's estrous cycle is something that we continue to study. In fact, a team of researchers at San Diego Zoo are currently leading a research project with the aim of "tracking the female polar bear estrous cycles and to determine pregnancy and reproductive cyclicity from both a behavioral and physiological perspective."
I, for one, am already excited to see their results!