Polar Bears: Dare to Hope

Chinook gives Kalluk's scruff a playful tug.

We’ve all experienced wanting something so bad that it hurts. People will tell you all kinds of things to make the waiting a bit less painful. You begin to fill your head with all the knowledge you can to know if it will really happen or not. And then comes the superstitions: don’t step on a crack, don’t talk about it, fingers and toes crossed. But no matter what, it just takes time to get the really special things that you want! What am I talking about? Wondering if polar bear Chinook is going to have cubs, of course! Is there anything else on our minds? Dare we hope?

As you know, Chinook and Kalluk marked Valentine’s Day 2011 by marking the start of the polar bear breeding season. If you were to ask Kalluk, he would tell you it was a successful season. The good news is that Chinook did not go back into season. This is very good, as we believe that when a female polar bear ovulates and there is fertilization, in most instances she will not cycle again that year. This is a good knowledge point.  Chinook, as many of you have observed, has also been putting on weight. This would not be due to carrying cubs, as they are barely over a pound at birth, but would make sense that her metabolism would compensate to hold as much as possible to nurse and provide for cubs—another good point of knowledge.

Polar bears experience delayed implantation, so we would expect to see Chinook changing behaviorally once the fertilized egg implants, around 60 days before birth. Yes, she is beginning to seclude herself away from Kalluk and Tatqiq. If gestation is 195 to 265 days for a polar bears, then from the 10 days of breeding, Chinook would be due between August 28 and November 16. Panic—it’s already September! Breathe, breathe. With such a long gestation, she could be implanting right now with a due date of early November.  Most polar bear births in North American zoos have occurred in the first week of November, the earliest was on October 13. Good things to know!

We have been collecting fecal samples for hormone analysis with the research branch of the Cincinnati Zoo and urine samples for hormone analysis with the Memphis Zoo. So far, nothing conclusive from the urine analyses, but the fecal analyses look positive for pregnancy. . .or pseudopregnancy. BUT—and yes, a big but—Chinook’s hormone profile is consistent with profiles of other polar bears that have given birth! Dare we hope?

So with knowledge in place, we’re avoiding walking under ladders, stepping on cracks, saying anything to jinx it, and above all, fingers and toes crossed. You better believe we are daring to hope that this time will be for sure!

JoAnne Simerson is a senior keeper at the San Diego Zoo. Read her previous post, Little Polar Bear: Lessons.