As you may know, polar bears Kalluk and Chinook bred late this spring. It is assumed but not confirmed that polar bear gestation is 195 to 265 days. If we count from the first day of breeding to the last, we would expect Chinook to give birth between November 2 and January 29! Most of you may be thinking it’s holiday season, autumn, winter, snow season, etc.. For us, it’s quiet season.
In early October we began preparations. First we set up all the charts to record Chinook’s behavior, weight, and den temperatures. We aim to have Chinook’s weight around 660 pounds (300 kilograms) at the time she would enter her den, and we look to have her den temperature right around 56 degrees Fahrenheit (13 degrees Celsius). Her behavior is completely up to her! We also began working with our veterinarians for ultrasound exams and our reproductive physiologist for thermal imaging exams. This is the first year we have tried thermal imaging on a polar bear, which has shown to be a good tool with Bai Yun, our giant panda. Ideally it would show increased heat indicating Chinook’s uterus gearing up for pregnancy. Of course, polar bear fur and skin is much denser than a giant panda’s, so this makes it a bit more challenging. And even ultrasound is challenging, as we are looking for very small changes in a very large bear.
So far, there is nothing to confirm a pregnancy, but the procedures are definitely a learning process. The great news, though, is that Chinook could not be a more willing patient. We are continuing to collect fecal samples and urine samples to be analyzed for several different hormones to see if one is a good indicator of pregnancy. The initial results from breeding through middle of summer looked promising; we will still have to wait, as it is still early, especially if she doesn’t give birth until January!
For now we are doing our best to set up a safe, secure, quiet environment for our girl. Her den was installed a few weeks ago, and we have given her two full bales of Bermuda hay. It is challenging not to rest in the big beds she has made—they look so comfortable! She also took a piece of sod from the polar bear yard and carries it to each bed to use as her pillow. We are careful not to disturb any of the preparations she is making. Every day we let her tell us what she wants to do. Currently, she seems to like to sleep in after breakfast and go out mid-morning for a nice swim and sun soaking. After about an hour or two she lets us know she would like to come back in, which we allow. We give Chinook her last meal of the day, and then she pretty much goes to bed. All we have now is the waiting! Is she or isn’t she? We just don’t know.
Kalluk and Tatqiq are both doing great. They are about to turn 12 at the end of this year. Tatqiq maintains her trim figure year round at 540 pounds (246 kilograms); female polar bears, for the most part, finish growing by the time they are 6 years old. Male polar bears, on the other hand, grow until they are 12 and can put on body mass for the rest of their lives. This year, our Kalluk not only gained back all the weight he lost during breeding season, when he had no interest in food, but is now up to 1,188 pounds (540 kilograms)! We thoroughly expect he will hit 1,200 pounds (545 kilograms) before he begins to lose interest in his meals for next year’s breeding season, if we have one! We may skip it if Chinook does indeed have cubs.
JoAnne Simerson is a senior keeper at the San Diego Zoo. Read her previous post, Polar Bears: Keeping Cool.