How can you tell if a polar bear is pregnant?

Written by Crissi Lanier & Shasta Bray

It’s not as easy as one would think. Dr. Erin Curry with our Center for Conservation and Research of Endangered Wildlife (CREW) is committed to finding a way.

The Cincinnati Zoo is currently home to two polar bears, Little One and Berit. Little One is a 24-year-old male and, despite his name, is the taller of the two bears. Berit is a 16-year-old female. She has a longer and leader body and face and sharper features than Little One. Plus her ears tend to stick out a little more. Polar bears can reproduce until about 26 years old and Berit is at a prime age for reproduction.  She and Little One have been together since 2007 and are observed breeding every year, yet Berit has never had cubs. We aren’t giving up yet.

In the meantime, Dr. Erin Curry has been working very hard in the CREW lab to develop a non-invasive pregnancy test for polar bears. It’s important for zoos to know when their polar bears are pregnant to be able to properly care for and monitor them. It is very difficult to determine if a female polar bear is pregnant because there is a period of time between mating and implantation of about 4 to 7 months, making it extremely difficult to know if breeding successfully resulted in a pregnant female. Polar bears also go through a period called pseudo-pregnancy, in which females show an increase in progesterone level similar to that of a pregnant female, but in the end there is no cub born. Pseudo-pregnancy also occurs in otters, wolverines, red pandas and some cat species. These factors make it extremely difficult to determine if a bear is pregnant. While there is not a definitive test yet, she has multiple projects underway that look promising.

Maybe the answer can be found in feces. Feces samples are very easy to collect without requiring invasive procedures. Samples from about 55 bears from 24 different institutions across North America and Canada are sent to Dr. Curry three times a year, packed in dry ice, to research any possible chemicals that may be present in pregnant bears but absent in others. She is also examining various protein levels in the feces and has identified five proteins that are higher in pregnant bears than in non-pregnant or male bears.  More research is needed and it is a very expensive test. The goal would be to develop a cost-effective and user-friendly test.

You may have heard about Elvis, the polar bear poo-sniffing dog. Elvis has been pretty successful so far in distinguishing between feces from pregnant and non-pregnant bears. Dr. Curry continues to try to determine what exactly Elvis smells that alerts him to the pregnancy. Read more about Elvis’ story here.

Another way to determine if a bear is pregnant could be through an ultrasound, but conducting one on a polar bear has its challenges. Dr. Curry along with Megan-Kate Ferguson (Curator of Animal Development and Training) and the bear keepers have been working with Berit to desensitize her to being touched so she can undergo medical procedures, such as ultrasounds, without sedation. Desensitization is a process by which the animal is touched through a training wall with an instrument, such as an ultrasound probe, over a period of time as the animal becomes less reactive to it and it becomes like a routine practice. The animal is rewarded throughout the process, called operant conditioning, to associate positive rewards with being touched. As the animal becomes more used to being touched, more actions and commands are added to eventually complete the behavior necessary for the procedure. It is a multi-step process that takes time and patience to develop an animal’s level of trust and comfort. Megan-Kate explains this process further in previous blog posts here.

Now that Berit is conditioned to being touched through the training wall while standing with her abdomen pressed up against it, the next step is to perform exploratory ultrasounds to find her uterus. Even though we know Berit is not currently pregnant, the ability to even find the uterus at all is important if performing ultrasounds is to become a reliable way of detecting pregnancy. Despite a polar bear’s large size, the uterus is small and very difficult to find. Polar bears have two uterine horns, each of which (in a non-pregnant state) is roughly the size of a pencil.

First, Berit is called in to the training area and asked to stand up at the training wall. When she completes this, she is immediately rewarded with ground meat treats. Megan-Kate then hoses her lower abdomen down through the wall; performing an ultrasound is more successful on a wet bear because a more solid connection is made between the bear’s skin and the probe. There can’t be any air or space between the probe and the skin, which is difficult due to her thick, fur coat. Once Berit is sufficiently wet, Dr. Curry uses the probe to search for the uterus. A transducer on the probe emits sound waves into the body and picks up the echoes as they bounce back from organs. The ultrasound machine then translates the information into a two-dimensional image of the bear’s insides that Dr. Curry interprets. During this time, Berit receives treats and constant positive reinforcement as she stands very still and calm.

On this day, Berit cooperated like a champ and Dr. Curry was able to find the bowels, but not the uterus. Maybe next time!  Even so, it was a successful day of continued training with Berit.

Solving the problems facing polar bear reproduction in zoos isn’t going to happen overnight, but it’s an ongoing challenge that Dr. Curry and the rest of the Zoo are committed to seeing through. Learn more here.

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