Hudson Meets Hope: Brookfield Zoo's Polar Bear Pair

The wait is over. Brookfield Zoo guests have noticed a new arrival at Great Bear Wilderness in recent weeks. Hope, a 5-year-old female polar bear who arrived at Brookfield Zoo this past January, and Hudson, the zoo’s 14-year-old male polar bear, recently were introduced to one another.

When Hope first arrived from Utah’s Hogle Zoo, she was able to explore and get acclimated to her new home at the zoo’s Great Bear Wilderness. Over the past several weeks, animal care staff began allowing the two polar bears to see and smell each other through mesh barriers behind the scenes before giving them access together in one of the outdoor habitats.

“We are happy to see that the introduction between Hudson and Hope is going well,” said Amy Roberts, senior curator of mammals for the Chicago Zoological Society, which manages Brookfield Zoo. “While the two bears are getting to know each other, guests may see them engaged in a variety of normal behaviors, including open-mouth displays, roaring, chuffing (a rapid jaw movement), and one bear following the other.” It’s also a positive sign that we have seen them eating together and sleeping close within sight of one other.” To allow them more space, for the immediate future, the bears also will have access to an indoor area.

Goals of Zoo Population Management
Hope’s transfer to Brookfield Zoo was based on a recommendation from the Association of Zoos and Aquariums’ (AZA) Polar Bear Species Survival Plan (SSP). An SSP is a cooperative population management and conservation program for select species in accredited North American zoos and aquariums. Each plan manages the breeding of a species to maintain a healthy and self-sustaining population that is both genetically diverse and demographically stable.

Science-based zoo population management requires balancing genetic, demographic, and husbandry concerns, and how we balance these really depends on the specific circumstances of the population being analyzed. Generally, we are aiming for populations that are demographically stable (i.e. large in size and breeding consistently) and genetically diverse. To maximize gene diversity, we try to select breeding pairs of animals that are descended from valuable genetic lineages and are also as unrelated to each other as possible.

In Hudson and Hope's case, they do have common ancestors. However, breeding between related individuals may be recommended occasionally in intensively managed zoo populations for a number of reasons.

Firstly, most zoo populations are closed populations, meaning migration into or out of the population is not possible. Some level of inbreeding becomes unavoidable over time in a small, closed population.

Secondly, in some cases, demographic concerns temporarily outweigh genetic concerns. For most populations, if we strictly selected pairs based on genetics, the populations would inevitably crash. For example, sometimes the most valuable female and male are socially incompatible. Other times, a population, despite a deceivingly large overall size, is actually really limited by its number of available breeders. Also, as we consider a potential breeder’s genetic value, age, breeding history, location, contraceptive history, medical needs, behavior, etc., it’s number of suitable matches might become even smaller.

Thirdly, occasionally breeding might be recommended between related individuals who are among the few remaining descendants of a very under-represented genetic line.

So, at the end of the day, if you are dealing with a population that has not already experienced a population bottleneck, notable inbreeding, or reduced fitness from a confirmed genetic disease, selecting a related pair to breed in order to meet demographic needs is not likely to have a detrimental impact on the population or any resulting offspring. If the pair is descended from under-represented genetic lines, it could actually help maximize population gene diversity. Any resulting offspring should be later paired with unrelated mates to avoid multiple generations of inbreeding.

Protecting Polar Bears
In the wild, polar bears are solitary except during the breeding season, which takes place from late March to early June, and when females are raising their cubs. In early fall, Hope will be given access to a den behind the scenes in the chance that she may be pregnant. The maternity den area at Great Bear Wilderness was specifically designed in the shape and dimensions of actual dens in the wild. If she does give birth, the area is equipped with cameras outside to allow animal care staff to observe the mom and cub(s) without disturbing them.

Polar bears are currently listed as a vulnerable species by the International Union for Conservation of Nature (IUCN). The main threat of the species’ decline is due to reduced access to their main source of food—seal—due to climate change melting the sea ice and other environmental factors. According to researchers, there are approximately 23,000-26,000 polar bears living worldwide today, including in and around Canada, Russian, and east Greenland.

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Posted: 4/13/2021 1:23:34 PM by Sean Keeley

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