Grizzly bear research at the WSU Bear Center: Assessing how hair cortisol concentration is affected by a short-term stress event

Recently, CWHC research scientist Marc Cattet visited the Washington State University (WSU) Bear Research, Education, and Conservation Center to assist with research on how cortisol (stress hormone) levels in the hair of grizzly bears are affected by short-term stress events that last no more than a few hours.

Photo: Jean-Pierre Lavoie (Wikimedia Commons)

The Bear Center is a unique facility dedicated to furthering the understanding and conservation of grizzly bears through research. The facility houses up to 12 captive grizzly bears, all of which were orphaned as cubs and would be unable to survive in the wild, or were removed from the wild because of human habituation. Bears at the center are trained through a reward system to enter a crate and present a limb for blood sampling, or lie still for other procedures (such as ultrasonography) to be performed, all while calmly snacking on dilute honey. This allows physiological research to be conducted without stress or the use of anaesthesia, which is a great advantage when compared to studying the physiology of free-ranging bears. Under free-ranging conditions, anaesthesia is a necessary procedure to allow safe handling of study animals. However, many physiological parameters are affected by anaesthesia which makes it difficult, if not impossible, to differentiate between anaesthetic effects and the effects of other factors of research interest.

In recent years, scientists are increasingly measuring the concentration of cortisol in hair as an indicator long-term stress in wild animals. Hair is a desirable biological sample because it can be collected without capturing and handling (ex. barbed wire hair snags). A common assumption is that the cortisol concentration in hair is determined by the amount of cortisol circulating in the blood combined with the rate of hair growth. This means that cortisol should not accumulate in hair during periods when hair growth has ceased. It also implies that cortisol levels in hair collected during a short-term stressful event, such as capture and handling, should not be affected because the hair growth that occurs over a period of no more than a few hours is too small to accumulate additional cortisol. However, a recent study by Marc and other collaborators presented findings from free-ranging bears that questioned the validity of these assumptions. As a follow-up to this study, the research team is further testing these assumptions by performing a confirmatory study on bears at the Bear Center. The study involves administering a synthetic analogue of a normally-occurring physiological substance known as adrenocorticotrophic hormone (ACTH) which elicits the release of cortisol into the blood circulation. This, in effect, simulates a short-term stress response as would be expected to occur in a grizzly bear during capture and handling. By measuring cortisol levels in the blood and hair, before and after ACTH administration, the researchers are able to determine if the hair cortisol concentration is affected a single short-term stress event. The first phase of this study was performed in April 2015 when hair growth is quiescent (not growing); the second phase will be carried out in July/August 2015 when hair growth is at maximum rate.

Due to the need for serial blood and hair samples, as well as the need to circumvent the potentially confounding effects of anaesthesia, this research could not be carried out without the unique research conditions provided by the Bear Center. Although studying bears in captivity does not replace the study of wild bears in their natural environment, certain types of studies such as this study would not be possible to carry out on wild populations. In this respect, it should be noted that the Bear Center collaborates only on research that will contribute to the understanding and conservation of wild bear populations.

This study is a three-way collaboration between the WSU Bear Research, Education, and Conservation Center, the Foothills Research Institute Grizzly Bear Program, and the CWHC.

Submitted by Erin Moffatt & Marc Cattet, CWHC National Office