Assessing Rates of Change in Bear Fecal Hormones

Principal Investigators

Jeffrey B Stetz, USGS Northern Rocky Mountain (NOROCK) Science Center, Glacier Field Station, Glacier National Park, West Glacier, Montana, 59936. jstetz@usgs.gov

Sam Wasser, Center for Conservation Biology, Department of Biology, and Department of Statistics, University of Washington, Seattle, Washington, 981195, wassers@u.washington.edu

Katherine C. Kendall, USGS-Northern Rocky Mountain (NOROCK) Science Center, Glacier Field Station, Glacier National Park, West Glacier, Montana, 59936. kkendall@usgs.gov

Introduction

Of the five remaining grizzly bear (Ursus arctos horribilis) populations in the lower 48 states, the Northern Continental Divide Ecosystem (NCDE) represents the largest number of individuals and the only large grizzly population contiguous with Canadian populations (Servheen 1999, Kendall et al. 2001). It is comprised of Federal, State, private, Tribal, and corporate land holdings, with only 9% of the 24,262 km being designated as private lands (Mace et al. 1996). Within the ecosystem there is a wide range of usage and degree of human development and disturbance, ranging from designated wilderness and National Park lands to residential subdivisions and commercial developments. Glacier National Park (GNP) represents a critical component of the NCDE in that it creates a large protective travel corridor between Canada and the southern extents of the ecosystem in the Bob Marshall Wilderness Complex.

Despite the relative protection of the NCDE, and GNP in particular, there is an ever increasing human presence within and surrounding this and every grizzly bear population in the lower 48 states. As conditions change for grizzlies a monitoring program needs to be developed that is founded on quantitative measures of the influence that humans have on the bears. It has been proposed that fecal hormones may be the key to monitoring stress levels of free-ranging animals. Stress hormones are processed into scat in response to threats to homeostasis or changes in metabolic demands (Moberg 2000). Scat can be collected noninvasively with minimal sampling bias over very large geographic and temporal scales (Kendall et al. 1992, Kendall et al. 2001). However, it is known that hormone, or glucocorticoid, levels within scat will change as a sample ages. This project is an effort to measure the direction and magnitude of these changes in a viable population of free-ranging bears.

Objectives

The primary objective of this study is to assess the direction and magnitude of change in stress hormone metabolite levels within individual bear scat samples over time. Measures of stress hormones such as corticosterone are quantifiable, unambiguous means to determine relative stress levels of individual animals within a given region (Wasser et al. 2000, Yalow 1978). However, until now only captive animals have been used to look at changes within samples over time given other variables such as diet, age-sex class, and reproductive status. While useful, there are undeniable differences between captive and free ranging animals and the conditions under which the scats may rest for an indefinite length of time. This study will be the first attempt to look at the rate of and variables related to the changes of hormone levels within scat.

One of the great benefits of sampling scat is the abundance of information that can be gathered from each sample. In addition to determining the changes in fecal hormone levels within a sample over time, we will also be able to ascertain the change in DNA amplification success rates as a sample ages. In order to develop a cost-effective population monitoring program it would be of tremendous benefit to understand how frequently trail surveys would have to be conducted to attain a desired degree of amplification success.

Finally, we are comparing the influence of collection and preservation methods on both DNA amplification as well as hormone metabolite levels. Up to 14 subsamples per scat (seven subsamples at two collection points) were collected. We are attempting to determine the most logistically feasible collection/preservation method while learning the characteristics of each with regards to intra-sample change over time. Mitigating the pros and cons of the different methods will allow researchers to potentially select one method to conduct large-scale sampling with.

Background

There is a pressing need for efficient, cost-effective methods for monitoring environmental health of wildlife populations over large geographic areas. A multitude of factors can impact environmental health in nature, including human disturbances such as habitat degradation, encroachment, geographic isolation, poaching, and presence of toxins. Distinguishing between this multitude of factors that can impact environmental health, and hence initiating timely mitigation, requires effective methods to track changes in the abundance and distribution of wildlife species, as well as the degree to which these species are impacted by human and other environmental disturbances.

Advances in molecular techniques and the continuing efforts to refine noninvasive sampling techniques are changing the options available to wildlife researchers and managers to study populations (Haig 1998). Scat surveys have been considered an obvious choice for noninvasive sampling, due in part to the abundance of fecal material deposited on trails and the ability of untrained personnel to conduct surveys (Foran et al. 1997, Wasser et al. 1997, Kendall et al. 1992, Putnam 1984). Furthermore, scat studies offer the unique opportunity to gather varied and important information about both individual animals as well as the population as a whole, including DNA, parasite loads, reproductive and stress hormones, and stable isotopes (Kohn and Wayne 1997). The need for sampling techniques that avoid the potential adverse affects of handling bears will also continue to increase. Adrenal response and subsequent elevated hormone levels have been linked to significantly lowered survivorship rates among handled African wild dogs (Lycaon pictus) in the Serengeti (Burrows et al. 1995), although this remains a very contentious issue (Creel et al. 1997). Parsons (1996) also suggested that inbreeding depression should be more pronounced in populations in a stressful environment.

Noninvasive genetic sampling (NGS) has become an ever increasingly popular term in the literature, but much remains to be proven as to the accuracy and reliability of the estimates provided by genetic sampling. The Greater Glacier Bear DNA Project is an excellent example of the promise and power of noninvasive sampling in wilderness areas. While most current NGS studies focus on collecting genetic material strictly through “hair corrals,” results of the Glacier project are showing that additional sampling techniques are necessary for multiple reasons. Among these are a curtailing of sampling biases relevant to mark-recapture analyses. “Sign surveys” were employed during all three years of fieldwork, with passively shed hair from rub trees as well as scat left on the trials of GNP being collected for genetic analyses. Results presented at the 13th annual IBA conference in Jackson Hole, WY (Kendall et al. 2001) showed that without this additional, independent sampling method a significant portion of the population would have been under-sampled. This information was acquired from the hair samples alone, as scat genotyping proved too problematic initially to complete. During the subsequent years techniques were significantly improved (Murphy et al. 2000) and currently the scat samples collected during the second field season are being genotyped.

The applications of scat in wildlife conservation will only continue to increase as new techniques are developed, refined, and validated. And as we become aware of the relationships between human disturbance and the physiological, behavioral, and reproductive responses of bears, it will be increasingly important that biologists accurately interpret and apply these techniques. However, without a means to ‘correct’ for the age, environmental conditions, and contents of a scat, it is difficult to accurately interpret the lab results.

Field Methods

During August - September 2001 we conducted trail surveys each day for approximately six weeks in the south-central portion of Glacier National Park. Each crew covered a section of trail approximately 12 miles in length, collecting each new scat encountered. As the trails were surveyed daily, we are confident that each scat was <24 hours old.

Each scat was divided into two portions: one for immediate collection, the second to be collected after a predetermined period of time. In addition, both of the portions were subdivided into up to seven different preservation techniques, depending on the size of the sample. This is an effort to determine if collection / preservation method has an effect on hormone levels that varies over time at different rates. Every effort was made to minimize disturbance of the sample to reduce bias between samples.

Recent fecal hormone field studies (i.e. Von der Ohe et al. in press) have demonstrated the need for detailed examination of dietary components as well as consideration of season of collection. We have developed a collection protocol to track variables previously identified in fecal collection studies as being potentially important in both fecal hormone monitoring as well as genetic sampling (Sam Wasser pers. comm.)

Results

Field Results:

Approximately 100 surveys were conducted between 9/1/01 and 10/31/01 in which 45 scat samples were collected. From these samples, approximately 540 subsamples were collected. With the assistance of the Division of Biological Sciences at the University of Montana, Missoula, MT we freeze-dried all subsamples.

Hormone Analysis:

Radioimmunoassays (RIA) were conducted in the laboratory of Dr. Sam Wasser Department of Zoology at the University of Washington, Seattle, WA.

Geographic Information Systems (GIS) layers have been created for sample distribution and will be used to determine if there are any confounding factors between scat origin and lab results. Considering the overall homogeneity of the area sampled we do not foresee any such factors arising.

As a pilot study, our objectives include developing an efficient protocol for sampling on a landscape scale given the inherent challenges of working with fecal hormones. As hormone levels change over time, it is critical that all samples be treated as identically as possible with all regards. Our fieldwork has already highlighted several issues that had not been addressed in previous hormone studies, such as variability in substrate between samples and how the contents of each sample affect the lyophilization (freeze-drying) process.

Data/Statistical Analysis: Data analysis have been completed. The manuscript is in prep.

Related Publications

  • Stetz, J. B., Addis E.A., K. C. Kendall, K. Hunt, and S. K. Wasser. Effects of environment, sample age, and preservation method on fecal hormones in wild grizzly bears (Scientific Poster). 16th International Conference on Bear Research and Management, Sept 27th-Oct 1st 2005, Riva del Garda, Trentino, Italy. Riva Del Garda, Trentino, Italy: USGS; 9 27, 2005.
  • Stetz, J. B., Addis E.A., K. C. Kendall, K. Hunt, and S. K. Wasser. Effects of environment, sample age, and preservation method on fecal hormones in wild grizzly bears. (in prep).

Field Crew

Sample Photographs

Cited References

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