Fecal Samples and Sexual Maturity

Polar bears in human care, like Ganuk and Henry, play an important role in the conservation of their species. They help us to gain a better understanding of polar bear biology, best welfare practices, and guide conservation of polar bear populations through participation in research studies   

The population of polar bears in American zoos is currently in decline, with birth rates only reaching about half of what is needed to be sustainable. Traditionally, zoos wait until a male is five or six years old before pairing him with a mate. However, evidence suggests that wild male polar bears have fathered cubs at two years old. By tracking hormone levels, researchers from the Center for Conservation and Research of Endangered Wildlife out of Cincinnati Zoo & Botanical Garden hoped to find a non-invasive way to identify the exact moment these young males hit sexual maturity. Finding an answer to this question could allow zoos to pair them up much earlier and give the population a much-needed boost. 

Due to how few polar bear cubs are born in human care each year, it took this dedicated group of researchers over a decade to collect enough data. They then had to analyze approximately 2,000 fecal samples from 14 male bears between the ages of 1 and 6. They looked specifically at testosterone metabolites, comparing the breeding season (January to May) against the rest of the year. A bear was officially dubbed "sexually mature" if his testosterone spiked during the breeding season and stayed elevated for at least ten weeks, effectively mimicking the biological patterns seen in fully grown adult males. 

Henry during the study in 2017!

Henry, one of our resident bears at the Cochrane Polar Bear Habitat fit all the criteria to participate in the study. Shortly after his arrival to the Habitat in 2016, animal care staff started collecting fecal samples at least once a week to send off to the researchers. This non-invasive sample method involved finding a fresh sample in Henry’s overnight den and collecting a golf ball sized amount of fecal matter into a labelled bag and placing it into the freezer.  

The results of Henry’s hormone profile were unique. Early on they found that his testosterone levels were at the highest in June, which is completely flipped compared to bears in North America. This interesting result could be related to sampling starting shortly after Henry moved to the Habitat from Sea World Gold Coast in Australia in the southern hemisphere. By 2018 and his hormone levels matched that of North American polar bears and he was considered sexually mature.  

A fecal sample from Henry

The results confirmed that there are individual differences as to when young male polar bears reach sexual maturity. One bear in the study reached the maturity criteria at just two years old, while three others were considered mature at age three. Generally, testosterone levels climbed as the bears got older and remained significantly lower during the non-breeding months. They also found that how the bear is raised, whether by their mother, human carers, or a mix of both, does not appear to have an influence on testosterone concentrations. 

The takeaway is that young male polar bears in human care facilities may be sexually mature by age two, similar to young male polar bears in the wild. Due to the variations between juvenile male bears in the study the scientists concluded that checking hormones alone isn't a perfect science for determining maturity. Instead, they recommend the use of hormone profiles alongside behavioral observations and, where possible, semen collection to make the best possible matches for the future of the species. 

With conservation being one of our core values, it is always exciting to have the opportunity to contribute to expanding our knowledge through participation in research studies. This study in particular provided us with a greater understanding of hormones in juvenile male polar bears and, in turn, how that knowledge could impact breeding practices. The non-invasive collection methods of the fecal samples used to determine hormone levels were a great example of how we can continue to expand our knowledge without interrupting the bears’ daily lives. We aim to support research-based conservation efforts whenever possible while maintaining best welfare practices and providing our bears the choice to participate.  

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