The Situation

Polar bear swimming

Polar bears (Ursus maritimus) are under threat due to climate change. They depend on sea ice to hunt seals and to find mates, but the decline in annual ice coverage is having deleterious impacts on polar bear survival and reproduction. Despite the worldwide popularity of this iconic species, little is known about how they will adapt to a changing environment. In response, zoos are striving to maintain a self-sustaining population that would provide opportunities to study the unique physiology of this species and serve as some buffer against extinction; however, despite concerted efforts to pair individuals for breeding, reproductive rates are poor overall.

The Goal

To better understand polar bear physiology and to pinpoint the cause of reproductive failure, CREW scientists are studying polar bears in zoos to characterize the reproductive physiology of this species. Additionally, they are pioneering assisted reproductive technologies, such as artificial insemination (AI) and semen collection, to preserve valuable genetic material and to complement natural breeding efforts.


polar bear laying on its back stretching

Scientists at CREW have analyzed samples from over 60 individual bears at 31 different institutions and, in doing so, have established the largest polar bear endocrine database in the world. The samples are used to monitor reproductive cycles, identify seasonal fluctuations in reproductive hormones and characterize sexual maturation; however, the ability to distinguish true pregnancy from pseudopregnancy continues to elude scientists. It is evident that a novel avenue must be pursued in developing a pregnancy test for polar bears and, by utilizing cutting edge scientific methods, CREW scientists are narrowing down candidate biomarkers that may be indicative of pregnancy. This non-traditional research path may finally yield an accurate, reliable, non-invasive pregnancy test. Furthermore, CREW scientists were among the first to collect and cryopreserve polar bear sperm and to perform an AI in this species. Although no cubs were produced following initial AI attempts, protocol refinement continues, and more is learned during every procedure.


The ability to non-invasively monitor reproduction in polar bears will illuminate the cause of reproductive failure and provide an invaluable tool for assessing the reproductive health of wild bears, which will be especially important as they face imminent environmental stressors. The reproductive research performed at CREW is contributing to the effort of saving polar bears with science. Moreover, the techniques being developed are likely to have broad application to other critically endangered populations.

Monitoring the reproductive processes of females  

Scientists at CREW have been studying polar bear reproduction since 2008 and have monitored over 55 bears at 24 institutions. Fecal samples are collected 3-7 times/week and assayed for steroid hormone metabolite concentrations, specifically testosterone and progesterone, which are indicators of ovarian activity and pregnancy/pseudo-pregnancy, respectively. Results indicated that fecal steroid metabolites may be used to indicate ovulation has occurred, but cannot be used to distinguish pregnancy from pseudo-pregnancy. Although fecal steroid concentrations have provided valuable insight into which females are experiencing estrus and ovulating, it does not allow for the discernment between pregnancy and pseudopregnancy.  A diagnostic pregnancy test not only would be useful in identifying pregnant females, it may also provide clues as to where the pregnancy process might be failing in so many of these females that fail to produce cubs. Additionally, the test may be useful in other species that experience pseudo-pregnancy as well, such as otters and red pandas.

Because we have exhausted all known tests of fecal products that have been used to diagnose pregnancy in other species, it is evident that a novel avenue must be pursued.

Fecal proteins

Specific proteins may exhibit altered profiles in the feces of pregnant bears, but predicting appropriate candidate proteins to investigate is speculative at best. Scientists at CREW are pursuing several methods for identification and quantification of proteins that might serve as indicators of pregnancy in this species; however, a major challenge associated with studying proteins in a fecal sample, instead of blood, is that they may break down in the intestinal tract or after excretion. Degraded proteins can be more difficult to measure because traditional methods of protein quantification rely on an antibody’s ability to recognize the protein’s intact structure. CREW scientists are exploring cutting-edge approaches that allow quantification of proteins and peptide fragments, regardless of the protein’s structure. Not only would the validation of a pregnancy biomarker be useful in diagnosing pregnancy, but it may also provide insight into the prevalence and timing of pregnancy loss that may be occurring in females that breed but fail to produce cubs and provide a novel means of monitoring population growth and reproductive health of wild bears.

Sniffer dog project (project completed)

Over three years, a detection dog was trained to distinguish fecal samples originating from pregnant bears from all other samples. Although “Elvis” consistently signaled positively on novel samples from pregnancies on which he was trained, he did not signal positively on novel samples from novel pregnancies. We suspect that he has either memorized the scent signatures of the pregnancies on which he was trained and has not generalized his recognition to novel pregnancies or that the scent signature of the samples changes with time, impacting his analysis. However, because he is able to distinguish the pregnant (post-breeding) from the non-pregnant (pre-estrus) state in those pregnancies, testing is underway to determine the earliest pregnancy may be detectable.

Fecal volatile organic compound (VOC) analysis (in process)

In a project closely related to the sniffer dog project, volatile organic compound (VOC) analysis was performed on over 40 polar bear fecal samples to identify the chemicals present in the airspace above fecal samples.  Of the 2705 different compounds identified, none was unique to pregnant bears or present in significantly higher concentrations in the pregnant versus pseudo-pregnant bears. Researchers at CREW are collaborating with analytical chemists to mine the complex dataset in an attempt to decipher the chemical signature associated with pregnancy.

Monitoring male seasonality

In an effort to determine the source of low reproductive success in polar bears in zoos, an important objective of CREW’s polar bear project was to characterize testosterone concentrations in males in zoos to verify that they are experiencing increases in testosterone during the breeding season. Furthermore, because bears in zoos generally live at lower latitudes and warmer climates relative to their wild cousins, they may provide insight into the ability of wild bears to adapt to a changing environment. In 2012, scientists at CREW completed a 3-yr study in which they monitored fecal testosterone concentrations in 14 adult male polar bears residing in 13 zoos ranging in location from Alaska to Arizona. Fecal samples were collected once per week year round, frozen, and shipped to CREW for analysis. Factors such as season, age, latitude, and the presence of females were evaluated to ascertain their effects on testosterone concentrations.

Results showed that testosterone is significantly higher during the breeding season (Jan-May) compared to the rest of the year, similar to wild bears. Even males that did not breed or were not housed with females experienced seasonal testosterone increases, albeit lower concentrations than breeding males. Testosterone was lowest in the younger males, peaked when a male is ~10-18 years old, and then decreased with old age.  Overall, latitude did not affect testosterone concentrations, although males at lower latitudes tended to exhibit lower testosterone during the summer months. It is unlikely that decreased testosterone in the summer would inhibit male fertility because the breeding season occurs at the end of the coldest months when testosterone concentrations were similar among all latitude groups.

In conclusion, males in human care experience seasonal fluctuations in testosterone appropriate to the breeding season, comparable to their wild counterparts. There is no evidence that diminished seasonal cues or seasonal asynchrony between the sexes is responsible for low reproductive success in zoos.  Results from this study do not reveal aberrations in testosterone production that would negatively affect the fertility of captive male polar bears.

Monitoring sexual maturation in polar bears

Polar bears in zoos generally are recommended for breeding starting around the age of five or six and then it may take a few years for them to conceive; however, recent DNA analysis of the wild population indicates that males as young as two or three may sire offspring and females as young as four can produce cubs. One of the aims of CREW’s Polar Bear Signature Project is to determine when juveniles become sexually mature; it is the first study to perform longitudinal fecal hormone monitoring on young polar bears throughout sexual maturation. With so few cubs born each year, it’s important that every sexual mature individual be paired for breeding to increase the chances of pregnancies and births.

Because there are so few young individuals in the zoo population, compiling a complete dataset has been slow, however; the preliminary results are in: data indicate that males and females as young as three begin exhibiting seasonal changes in excretion patterns of steroid hormone metabolites, suggesting the onset of sexual maturation. Interestingly, one three-year-old female even exhibited a pseudo-pregnancy, despite the fact that breeding did not occur. Deciphering the fluctuations in hormone patterns associated with sexual maturity may allow for more appropriate breeding recommendations and will establish a knowledge-base of normal hormone patterns for juvenile polar bears. Since longitudinal sampling from wild individuals is logistically challenging, information learned from the zoo population may be applied to their wild cousins as well.

Developing and Optimizing Assisted Reproductive Technologies (ART) in Polar Bears

Semen collection and cryopreservation.

Due to growing concern over reproductive failure in polar bears nationwide, CREW scientists are receiving requests from other zoological institutions to perform assisted reproductive procedures, such as artificial insemination (AI). A polar bear sperm bank is vital in supporting AI endeavors; however, the traditional method of semen collection from wildlife, electro-ejaculation, has been relatively unsuccessful in polar bears. Our compelling research has evaluated the use of a novel, minimally-invasive method of semen collection in this species. Although the mechanism is not well understood, there are reports of certain anesthetic drugs inducing ejaculation or causing semen to pool in the urethra in other species. One drug, medetomidine, seems to have this effect and is already commonly used to anesthetize polar bears in zoos. To retrieve the sperm, a catheter is threaded into the urethra, a syringe is attached to the end of the catheter, and the catheter containing the sperm is slowly withdrawn. The procedure can be performed opportunistically at the time of a regularly scheduled physical examination and takes less than 5 minutes, so it doesn’t require a lengthy extension of anesthesia time. This new approach has resulted in an impressive success rate and, for the first time, the creation of a polar bear sperm bank to store these valuable genetics is possible. A future goal is to perform semen collections on wild bears to preserve their genetics and also to investigate the impact of pollutants on the fertility of wild bears.

Additionally, CREW scientists have been investigating the use of novel semen extenders to protect semen during the cryopreservation process. Traditional extenders rely on ingredients whose composition may vary and that require special handling (i.e. egg-yolk). Preliminary investigations have demonstrated a commercially available extender is both as efficient at protecting polar bear sperm and easier to use than the traditional extenders, which greatly facilitates semen cryopreservation efforts.

Artificial Insemination (AI). Due to the shortage of males, potentially reproductively viable females are left without a male to breed. Consequently, the demand for developing ART is growing; however, little is known of the hormones orchestrating the intricacies of female reproduction in this species. Unlike humans and domestic species, information is non-existent regarding the use of exogenous hormones to overcome infertility in polar bears. Additionally, the need to determine the timing of hormones relative to performing an AI procedure is important to ensure that the insemination is performed around the time of ovulation. We have demonstrated successful ovulation induction in a polar bear using exogenous hormones; however, the results have been variable among individuals, so the precise hormones, dosages, and timing of administration relative to AI warrants further examination. Establishing a polar bear sperm bank and optimizing ART in this species will provide opportunities for conception to females that otherwise would not have a chance of pregnancy.

Until recently, collecting blood from polar bears has been considered an invasive procedure, as it commonly requires anesthesia; however, advances in animal training techniques are now permitting animal care staff to collect serum samples from polar bears, voluntarily and regularly. The ability to analyze serum, from which a more diverse panel of hormones can be detected, opens new doors for monitoring reproductive health in this species. The first investigation into serum hormones by CREW scientists focused on Anti-Müllerian hormone (AMH) and has already provided interesting insight into the reproductive physiology of this species. AMH is produced by the ovary and is used to assess fertility in other species, including humans. Scientists at CREW successfully validated an assay to measure AMH in polar bears and then quantified the hormone in previously banked blood samples. Preliminary results showed that AMH concentrations decline with age, reaching their lowest concentrations around the age of 20 in females. AMH holds promise for assessing which individuals have the best chance at producing cubs and consequently can be used to prioritize breeding recommendations, which is important considering that cubs are greatly needed to maintain the population. Additionally, a more thorough understanding of AMH may be beneficial in monitoring wild bears, whose fertility may be impacted by environmental pollutants.

Birth control that worked too well

Unlike castration, which results in permanent sterility, hormonal contraceptives are considered to be temporary and reversible and, consequently, they play an integral role in managing animal population growth. Many polar bears in zoos were administered contraceptives in the early part of the 21st century due to lack of exhibit space and decreased need for additional zoo-born cubs. But more recently, the demand has risen and polar bears currently are in high demand. Contraceptive treatments were discontinued and nearly all females of reproductive age were paired for breeding; however, very few cubs are produced each year.

From 2008 – 2016, CREW scientists monitored the fertility of ~30 mature female bears across North America, roughly half of which have been treated with contraceptives. Although the females that had been contracepted resumed normal breeding behaviors following treatment, only two (18%) gave birth. Both of these females had received just a single type of contraception whereas others had received different or multiple types over the years. In comparison, nearly 53% of the females that had never been contracepted produced cubs.

A number of factors probably contribute to poor fertility, such as advanced maternal age and whether or not individuals had produced cubs prior to treatment, but it does appear that certain hormonal contraceptives have had unintended long term deleterious effects on the fertility of this species. Although it is unknown as to where, exactly, the pregnancy process is failing, CREW scientists are examining ways to overcome infertility to give these females a chance at motherhood.

You don’t have to travel to the Arctic or work in a lab to help save polar bears. Below is a list of actions anyone can take to ensure that polar bears exist for years to come:

  • Save energy by adjusting your thermostat 2-3 degrees lower in the winter and 2-3 degrees higher in the summer.
  • Reduce emissions by walking, riding a bike, carpooling, or taking public transportation instead of driving a car. If you have to drive, buy a low emissions vehicle.
  • Support CREW’s Polar Bear Signature
  • Consider how your diet impacts the planet. Reduce your consumption of animal products and consume foods that are minimally processed and packaged (ex- potatoes vs. potato chips).
  • Vote for elected officials who will work to take action on climate change.
  • Replace light bulbs with energy-efficient LED bulbs.
  • Minimize your consumption—reduce, reuse, repurpose, and recycle!
  • Buy products created closer to home: for example, if you live in the U.S. or Canada, purchase goods made in North America instead of those shipped from far away.

We’re proud to be featured in peer-reviewed publications and conference proceedings. See the full list below.

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Recent peer-reviewed publications:

Curry E, Skogen M, Roth TL. (2020). Evaluation of an odor detection dog for non-invasive pregnancy diagnosis in polar bears (Ursus maritimus): Considerations for training sniffer dogs for biomedical investigations in wildlife species. Journal of Zoo & Aquarium Research (accepted- in press)

Bourque J, Desforges JPW, Levin M, Atwood TC, Sonne C, Dietz R, Jensen TH, Curry E, McKinney MA. (2020). Climate-associated drivers of plasma cytokines and contaminant concentrations in Beaufort Sea polar bears. Science of the Total Environment 745:140978.

Curry E, Easley JS, Wojtusik J, Roth TL. (2020) Identification of mink (Neovison vison) fecal proteins during embryonic diapause and placental pregnancy for non-invasive pregnancy diagnosis in wildlife. Bioscientifica Proceedings 10:101-112.

Steinman KJ, O’Brien JK, Fetter GA, Curry E, Roth TL, Owen MA, Robeck TR. (2017). Enzyme immunoassay analysis for androgens in polar bear (Ursus maritimus) urine using enzyme hydrolysis. Aquatic Mammals. 43: 245-253

Curry E, Safayi S, Meyerson R, Roth TL. (2015). Reproductive trends of polar bears in zoos (Ursus maritimus) in North American zoos: a historical analysis. Journal of Zoo and Aquarium Research 3:99-106.

Curry E, Wyatt J, Sorel L, MacKinnon KM, Roth TL. (2014). Ovulation induction and artificial insemination of a polar bear in zoos (Ursus maritimus) using fresh semen. Journal of Zoo and Wildlife Medicine 45:645-649.

Curry E, Roth TL, MacKinnon KM, Stoops MA. (2012). Factors influencing annual fecal testosterone metabolite profiles in male polar bears in zoos (Ursus maritimus). Reproduction in Domestic Animals 47:222-225.

Stoops MA, MacKinnon KM, and Roth TL (2012). Longitudinal fecal hormone analysis for monitoring reproductive activity in the female polar bear (Ursus maritimus). Theriogenology 78: 1977-1986.

Curry E, Stoops MA, Roth TL. (2012). Non-invasive detection of candidate pregnancy protein biomarkers in the feces of polar bears in zoos (Ursus maritimus). Theriogenology 78:308-314.

Conference proceedings:

Counsell KR, Landero JA, Roth TL, Curry E. (2019). Poster presentation. Identification and quantification of steroid hormones in polar bear (Ursus maritimus) feces by HPLC. International Society of Wildlife Endocrinology 7thInternational Meeting. Kruger National Park, South Africa (October 13th-16th).

Curry E, Easley JS, Wojtusik J, Roth TL (2019). Oral presentation. Evaluating mink fecal proteins during embryonic diapause and placental pregnancy for non-invasive pregnancy diagnosis. 3rd International Symposium on Embryonic Diapause. Ascona, Switzerland (June 2nd-6th).

Curry E, Stoops MA, Roth TL (2019). Poster presentation. Fecal metabolite monitoring as a tool to assess sexual maturation in polar bears. Proceedings of the International Embryo Transfer Society 45th Annual Conference. New Orleans, LA (January 20th-January 23rd).

Kennedy VC, Roth TL, Donelan EM, Curry E. (2018). Poster presentation. Western blot evaluation of fecal transthyretin (TTR) for use as a pregnancy test in polar bears (Ursus maritimus); In search of the golden compass of population management tools. Proceedings of the Society for the Study of Reproduction 51st Annual Meeting. New Orleans, LA (July 10th-13th).

Curry E and Roth TL. (2017). Poster presentation. A rapid method of semen collection from polar bears immobilized with medetomidine. Proceedings of the 22nd Biennial Society for Marine Mammalogy. Halifax, Nova Scotia (October 22nd-27th).

Curry E, Roth TL, MacKinnon KM, Stoops MA. (2016). Monitoring the long-term effects of contraceptives on the fertility of polar bears in zoos (Ursus maritimus). International Congress on Canine and Feline Reproduction. Paris, France (June 22nd-25th).

Curry E, Stoops MA, DeLorenzo CJ, MacKinnon KM, Roth TL. (2016). Using the ex situ population to advance the reproductive science of polar bears. 24th International Conference on Bear Research and Management. Anchorage, AK (June 12th-16th).

Curry E and Roth TL. (2016). Poster presentation. A rapid, minimally-invasive method of collecting semen from polar bears. Proceedings of the International Embryo Transfer Society 42nd Annual Conference. Louisville, KY (January 23rd-January 26th).

DeLorenzo C, Lynch B, Roth T, Petren K, Curry E. (2016). Poster presentation. Development of a non-invasive, fecal protein pregnancy test for polar bears. Proceedings of the International Embryo Transfer Society 42nd Annual Conference. Louisville, KY (January 23rd-January 26th).

Curry E, Skogen M, Roth TL. (2014). Oral presentation. Evaluating the use of a detection dog and volatile organic compound analysis for non-invasive pregnancy diagnosis in the polar bear (Ursus maritimus). 23rd International Conference on Bear Research and Management. Thessaloniki, Greece (Oct 5th-11th).

Curry E, Roth TL, MacKinnon KM, and Stoops MA. (2012). Platform presentation. Seasonal variation in fecal testosterone metabolite concentrations in male polar bears in zoos (Ursus maritimus). International Conference on Canine and Feline Reproduction. Whistler, BC (July 26th-29th).

Roth TL, MacKinnon KM, and Stoops MA.  (2011).  Non-invasive fecal hormone monitoring for evaluating polar bear (Ursus maritimus) reproductive activity.  Proceedings for the 20th International Conference on Bear Research & Management. Ottawa, ON (July 17th-23rd).

Stoops MA, Vollmer L, and Roth TL. (2009).  Faecal steroid analyses for monitoring reproductive function in polar bears (Ursus maritimus).  Reproduction, Fertility and Development 21(1) 182-183.

Roth TL, MacKinnon KM, and Stoops MA.  (2009).  Noninvasive fecal hormone monitoring for assessing reproductive activity and diagnosing pregnancy in the polar bear (Ursus maritimus).  Proceedings for Advancing Bear Care 2009, Bear Care Group.  San Francisco, CA.

Collaborative Research

Investigating the relationship between ambient conditions and thermoregulatory responses in polar bears (University of Guelph). By understanding links between thermoregulation demands and stress, adjustments for the environment of polar bears in zoos could be suggested to reduce temperature-associated stress thus improving the probability of successful breeding in zoos.

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Photogrammetry analysis of polar bear images (Purdue University, University of Wyoming, and Polar Bears International). As part of the Polar Bears International citizen science project in Churchill, Manitoba, Canada, researchers are using polar bears in zoos to optimize methodologies used to study the wild population. They are developing photographic methods to measure body condition to monitor long-term trends in morphometric changes related to alteration of environmental conditions.

Fecal near infrared spectroscopy (NIRS) (Texas A&M). Dried fecal samples from pregnant and non-pregnant bears are scanned using a spectrometer and measurements of reflectance are recorded over the visible and near infrared ranges. If differences are found, this method could provide a non-invasive means of pregnancy diagnosis in this species.

Exploring the metabolomic signature of pregnant polar bears (Cincinnati Children’s Hospital). Scientists at the Cincinnati Children’s Hospital Medical Center are characterizing the metabolites in polar bear fecal samples to determine if specific biomarkers or patterns are unique to pregnancy. Studies are underway to evaluate the metabolites in hundreds of samples.

Polar bears (Ursus maritimus): connections between activity levels, temperature and day length (Miami University). The activity levels of zoo-housed bears at multiple facilities were assessed in relation to temperature and hours of daylight. Results of this study may help to define the conditions that polar bears in zoos should be housed in to enhance their health and behavior.

 Comparison of fecal and urinary steroid hormone excretion patterns in polar bears (SeaWorld San Diego). The aim of this research is to compare steroid excretion patterns in urine and feces collected from polar bears in zoos, especially those undergoing treatment for infertility. Characterization of various metabolite patterns will provide insight into the reproductive processes of this species.

Evaluation of urinary and fecal hormone metabolites in pregnant polar bears (Memphis Zoo). This study aims to compare urinary and fecal steroid hormone excretion patterns in pregnant and non-pregnant polar bears.

Annual fecal glucocorticoid metabolite concentrations in pregnant and pseudopregnant polar bears (Ursus maritimus) in North American zoos. (Brookfield Zoo) The goal of this study was to determine if glucocorticoid concentrations are higher in the feces of pseudo-pregnant polar bears versus pregnant bears.

Patterns of diversity in the indigenous microbiota of mammals in human care (Stanford University) Researchers are investigating the various microbes present in the guts of many animals, including polar bears.

Analyzing Hormone Patterns of Male Polar Bears In Human Care Under Different Social Conditions (Canadian Polar Bear Habitat and York University). Testosterone alters behaviors and aggression levels in other species, and previous research has shown that the presence of female polar bears increases testosterone concentrations in males; however, no studies have focused on testosterone concentrations of bachelor groups. A better understanding of the impacts of conspecifics and group housing on male testosterone concentrations may inform behavioral management and better define welfare standards.

Validation and Quantification of DHEAS in Polar Bear Feces (University of Alaska Fairbanks). Dehydroepiandrosterone (DHEAS) is a steroid hormone precursor that has been correlated with reproductive success in many species. Concentrations of DHEAS will be quantified in fecal samples collected from zoo bears and compared to those of wild bears.

Arctic Ambassador Center

With CREW’s expanding involvement in polar bear research, conservation and education and the Zoo’s progress in going green, it was a natural next-step to formally name the Cincinnati Zoo & Botanical Garden one of Polar Bears International’s official Arctic Ambassador Centers. PBI Arctic Ambassador Centers are organizations endorsed by leading polar bear scientists and the AZA for actively engaging in saving polar bear habitat through greenhouse gas reductions within their organizations and communities. As such, CREW and the Zoo are committed to: 1) providing information about climate change to the local community on Zoo grounds, on the website and through special programs, 2) actively reducing our own carbon emissions and 3) maintaining our polar bears in an exhibit that meets all AZA standards.

In return, we receive: 1) access to educational materials and biofacts from PBI, 2) support from PBI staff, 3) special opportunities for social networking and public relations and, perhaps most important, 4) the opportunity to engage in several unique PBI education programs.