polar bear reproduction


Tatqiq: Odd Bear Out

Tatqiq is sure to enjoy Snow Day on Saturday, May 17, 2014!

Tatqiq is sure to enjoy Snow Day on Saturday, May 17, 2014!

Breeding season for polar bears is typically January through June. For Kalluk and Chinook in particular, it can happen anytime in that window. This year, the breeding window began on April 23, 2014, and usually lasts anywhere from 4 to 14 days. In 2013, it occurred in January and only lasted four days. This year, we are seven days into the process and breeding is still happening. However, the frequency has diminished quite a bit from the first few days.

Science still knows very little about polar bear reproduction. What we do know is that polar bears are both induced “ovulators” and delayed “implanters.”

Induced ovulation means that the females don’t have a normal estrus cycle like many mammals do. Male bears follow around females for days or weeks at a time, “wining and dining” them until they are receptive to breeding. Once ovulation is induced, then breeding will commence.

Delayed implantation is tricky because it makes gestation periods and birth dates difficult to predict. Unlike most mammals, after polar bears successfully copulate, they are not immediately pregnant. The fertilized egg remains in a suspended state until conditions are right, at which point the egg implants in the uterus and gestation can begin.

Until late May/early June, Tatqiq is, unfortunately, the odd bear out. Chinook’s hormones are raging, and she is less tolerant of Tatqiq during this time period. Kalluk generally does a good job of breaking up squabbles and moving his sister to a safer spot away from Chinook. If you have been watching the Polar Cam in recent weeks, you have probably noticed Tatqiq seeking refuge in the back corner near the waterfall. This is her safety zone and the spot where she feels she can best defend herself. It is our job as keepers to recognize these changes in behavior and adapt our management strategy. Because of the increased tension between the two females, you will usually only see Kalluk and Chinook on exhibit after 12:30 p.m. When the keepers pull the bears off exhibit for their final meal of the day, we give Tatqiq the polar bear penthouse where she has her own private pool, grass, trees, and air-conditioned bedrooms.

Once breeding season is over, you will again see Kalluk and Tatqiq playing together and there will be less aggression between the two females. Be sure to watch the action daily on Polar Cam!

The Polar Bear Team


Is Chinook Pregnant?

Chinook, left, and Kalluk frolicked in the snow a few months ago.

Chinook, left, and Kalluk frolicked in the snow a few months ago.

Around this time of year for the past few years, the number one question we are asked by those familiar with our polar bears is “Is Chinook pregnant?” We nearly always answer with “We sure hope so, but….” Some of you may wonder why we are so elusive with our answer year after year. There are a number of reasons, none of them clandestine. Mainly, the polar bear community is still searching for all the answers. Things are complex in the polar bear world!

Did you know that polar bears have a wide range for gestation, spanning from 164 to 294 days in the wild (195 to 265 days in managed care)? If we determined possible birth on this information alone, this year Chinook could have given birth from July through September, based on when she bred with our male, Kalluk. However, we are aware of research that has studied historic data of births of wild bears and with other observations in the wild. It is hypothesized that date of breeding may not solely determine date of possible birth. Instead, it is a little more complicated than counting days from breeding time. Births generally occur between November and December, with the occasional birth outside those months even when breeding occurs in January, for example (when Kalluk and Chinook bred). Lastly, female polar bears have both induced ovulation and delayed implantation, which makes determining timing and the triggers involved difficult.

We are trying! Through research, we are continuing to learn more and more. Every other day, we collect urine samples from Chinook and fecal samples three times per week, all for hormone analysis. With Chinook’s full cooperation, we perform ultrasound exams weekly once her den is in place. (The den was set up this year at the end of September.) Through research and collaboration, we hope to gain new insights into the complexities of polar bear reproduction and give you more definitive answers in the future to the question, “Is Chinook pregnant?”

The Polar Bear Team, San Diego  Zoo

Watch the bears daily on Polar Cam.


Polar Bear Ultrasound

Will these two become parents this year?

Pieces of the Puzzle

Yes, we have begun the ultrasound exams with Chinook! Yes, she is cooperative, and we are very hopeful that this will be the year that once again we will have polar bear cubs at the San Diego Zoo. But how difficult is it to ultrasound a polar bear who is wide awake? The pieces of the puzzle are coming together.

The first puzzle piece, training, was relatively easy. Due to the great trusting relationship between Chinook and her keepers, and the history of learning together, teaching Chinook to roll over and hold went quickly. The next part was to get her to accept the ultrasound gel and actual probe on her belly. Chinook does very well with it all. And please keep in mind she is the only polar bear in the world who is trained for the ultrasound procedure.

We tend to take for granted the use of ultrasound to diagnose pregnancy. It is almost commonplace now. It wasn’t that long ago when ultrasound exams on our giant panda Bai Yun were also history in the making! Again one of the challenges is to find a very small fetus in a very big bear and ensure the safety of Chinook, the veterinarian, and, of course, the ultrasound probe! We are lucky to have many talented folks at the Zoo who have helped in designing and building various pieces of the puzzle. We now have a specially molded probe holder and removable bars on our training crate that allow for better movement of the ultrasound probe.

Every ultrasound image is recorded for review by our veterinary staff. We are confident that “when” (positive thinking) polar bear cubs begin to develop, we will be able to see them well and document another historical event: first-ever in utero polar bears!

Until then, we continue to collect urine and fecal samples to chart Chinook’s hormonal changes and monitor her behavior for dramatic and subtle changes that will alert us to her needs for a successful pregnancy and rearing of polar bear cubs. The cameras, microphones, and recorders are all ready, as long as she chooses those areas to den!

Now that we have all the pieces to the puzzle for our Chinook, it is important to remember that there are many pieces of polar bear reproduction that are missing. Much of our research with polar bear sensory ecology (see post Polar Bears: Getting Ready) will help shed light on pieces of the puzzle that would be very difficult, if not impossible, to do in the Arctic. To be able to document a polar bear pregnancy may give us more information on how to better protect polar bear maternity areas at critical times as more environmental impact jeopardizes the survival of our wild polar bears. How wonderful to be part of keeping polar bears in our future and not just a part of our history.

JoAnne Simerson is a senior keeper at the San Diego Zoo. Read her previous post, Polar Bears: Dare to Hope.

Update October 28, 2011: Both ultrasound and fecal hormone analysis look possible, but nothing is confirmed yet. Keep everything crossed!


Polar Bear Spring

Kalluk refocuses his energy.

Spring arrived at the San Diego Zoo’s Polar Bear Plunge a few days early this year. Chinook and Kalluk began breeding on March 17 and then abruptly stopped on March 24. Last year, the season lasted from February to June! Although it’s possible we could see more, we are not expecting it to be likely. Chinook’s behavior gives us no indicators like last year that she will cycle again, and even though Kalluk has shown some behavioral frustration, he has not shown any interest in Chinook for almost a month. So what could this mean?

First, we really don’t know exactly what happens in polar bear reproduction. We do know that breeding season happens in the spring, typically March through May. It is strongly suspected that female polar bears are spontaneous ovulators, meaning they will ovulate only when breeding occurs. It is also suspected that she will not cycle again if, in a breeding season, fertilization occurs. This has some evidence to the contrary, as we do know of some cubs in the wild that share different fathers!

For argument’s sake, let’s agree that for females their breeding season ends with a fertilized egg. That would mean that Chinook has a blastocyst or two floating around in her uterus waiting to implant! Remember: polar bears have delayed implantation, giving them a gestation of 195 to 265 days, so we’ll be anxiously waiting until sometime between October 1 and December 9 this year…unless we see a return in Chinook’s interest to Kalluk. Sigh! Yes, we do plan to do ultrasound checks on Chinook as we get closer to October, so perhaps we’ll get an earlier clue. We are so lucky to have the world’s only polar bear trained for ultrasound procedures! (Watch video of an ultrasound session with Chinook from 2009.)

Kalluk also is beginning to show less anxious pacing than we normally see during breeding season. Although afternoons seem to bring about some surges, he is beginning to play and eat like his true self. During breeding season, he is so distracted we do all we can to get a few pounds of food into him. Currently, he is consuming up to 50 pounds a day. Yes, he is on his way back!

Tatqiq has had an easier time this year as well. Last year, Chinook kept her sitting up by the waterfall every day. Even though we always gave Tatqiq a choice to stay in the bedroom area, she always wanted to go out. This year she definitely gained some self confidence and became our little savvy politician and was granted privilege to use the entire exhibit.

All three bears love their new “polar bear park” (see post Polar Bears: The Countdown). It used to be that the San Diego Zoo was famous for its green polar bears, due to algae growing in their hollow hair follicles. We’ve not seen that for many years now with our improved water. But now, with the long, lush grasses of the polar bear park, our beautiful white bears are experiencing green grass stains from rolling on the knolls and down the hills! Chinook had the most lovely green cheeks yesterday morning.

This week will also bring changes to the neighborhood: our long-awaited Arctic foxes will be moving in. Arctic foxes have a very strong aroma! It will be quite interesting to watch Chinook, Kalluk, and Tatqiq as they check out their new neighbors, first by aroma and then by sight! I’m sure we’ll have photos up once the foxes settle in. Keep a look out!

JoAnne Simerson is a senior keeper at the San Diego Zoo.


Polar Bears: What Little We Know

Chinook: Is she or isn't she?

Chinook: Is she or isn't she?

We are anxiously awaiting the sounds of polar bear cubs squawking, humming, and crying in Chinook’s den. But we really have very little idea of when that sound will reach us because we still have much to learn when it comes to polar bear reproduction. Like other bears, the polar bear exhibits reproductive characteristics that are perfectly tailored to their environment. Without these adaptations, reproduction in the extreme, often harsh, climate of the Arctic, would not be possible.

Delayed implantation is just one of the adaptations polar bears have developed to cope with the challenges of life in the Arctic. This adaptation make predicting just when to expect newborn cubs quite a challenge.

Delayed implantation is a phenomenon common among all bears—at least we think! It serves its most obvious function in bear species that inhabit highly seasonal environments—that is to say, environments where food and good weather are not available year round. The more extreme the environment, the longer the delay: polar bears in the high Arctic are thought to delay implantation for about five months, whereas polar bears in more southerly latitudes may delay implantation by about three months. During this delay, regardless of how long it is, females go through an intensive feeding period during which they will gorge themselves on ringed and bearded seals for as long as possible before denning up in the fall. This summer feast allows them to deposit a thick layer of blubber that provides the essential nutritional support needed during the extended fast associated with pregnancy and denning.

True gestation takes about 60 days and typically begins in the fall, soon after pregnant females excavate and enter their subnivean (undersnow) dens. Females will remain in their dens until spring emergence, cubs in tow, ready to face the elements and begin the neverending search for food.

Fall will soon arrive in San Diego. Although it will be months before a chill wind is in the air, the change in day length (the first day of fall is that day when days begin to be shorter than nights) may cue hormonal and behavioral changes that prepare the polar bear for implantation, pregnancy, and impending motherhood. We are all watching Chinook with great anticipation: Is she or isn’t she? And when will she?

For a bear like Chinook, living at the San Diego Zoo where the weather is warm and food is always available, a layer of blubber is probably not necessary for successful reproduction. However, she has put on weight, and we are hoping that this is a sign that we will hear those hums and squawks from the den in the next couple of months. Stay tuned!

Megan Owen is a conservation program specialist at the San Diego Zoo. Read her previous post, Speaking of Polar Bears in Beijing.

Watch the bears daily on Polar Cam.