Monitoring Bear Populations with Non-Invasive Sampling 2008 - 2014


  • Evaluate the efficacy of monitoring grizzly and black bear population trends using noninvasive hair sampling at a landscape scale.
  • Estimate population: (1) growth rate, (2) abundance, (3) distribution and relative density, (4) gene flow and genetic structure, and (5) apparent survival rates.
  • Provide area-specific information on bear population status.


North American range map for grizzly bears (Ursus arctos)Grizzly bears (Ursus arctos horribilis) once roamed most of the North American continent. Habitat destruction and direct conflicts with humans have reduced their range by 99% in the lower 48 states (right, click on map for larger version). In 1975, all grizzly bears south of Canada were listed as threatened under the Endangered Species Act. The Northern Continental Divide Ecosystem (NCDE) in northwest Montana is one of six recovery zones defined in the Grizzly Bear Recovery Plan (U.S. Fish and Wildlife Service 1993). The NCDE is the third largest in area, harbors the greatest number of grizzly bears, and is the only zone contiguous to a strong Canadian population. For these reasons it may have the best prospect of long-term survival in the contiguous (48) states. For more information about grizzly bear recovery, visit the U.S. F&WS Grizzly Bear Recovery Office webpage.

Wildlife managers need reliable estimates of population status and changes to make informed decisions about how to recover at–risk populations, yet typically these estimates are costly to obtain and are often imprecise. Although the grizzly bear (Ursus arctos) population in the Northern Continental Divide Ecosystem (NCDE) of northwestern Montana has been managed for recovery since being listed as threatened under the U.S. Endangered Species Act in 1975, no rigorous data had been available to evaluate the program’s success. A recently completed U.S. Geological Survey study, the Northern Divide Grizzly Bear Project (NDGBP), provided detailed information on grizzly bear abundance, relative density patterns, population genetic characteristics, and distribution in the greater NCDE (Kendall et al. 2009). However, there have been no reliable estimates of population growth rate or other trends, such as changes in density patterns, in this population. The Montana Department of Fish, Wildlife, and Parks is leading a grizzly bear population trend monitoring program in the NCDE that uses vital rate estimates from radio–collared grizzly bears to produce a single, population–wide estimate of growth rates (λ; lambda). Monitoring began in 2004 and the first estimate of lambda based on reasonable samples sizes of adult and subadult bears is expected in 2010 – 2012.

Considerable amounts of time and money are allocated to manage grizzly bears. Effective and efficient programs to monitor changes in population abundance, distribution, and connectivity are vital to identify appropriate actions to ensure the persistence of populations. Wildlife population monitoring programs should serve two primary purposes consistent with adaptive management: (1) provide periodic assessments of the status and trends of population metrics of concern, and (2) improve our understanding of how populations respond to management actions (Pollock et al. 2002, Nichols and Williams 2006). As such, effective monitoring programs must acquire the information needed to make management decisions in a useful timeframe, as well as provide insight into the nature of the parameters being monitored and the factors impacting them (Nichols and Williams 2006). Predicting the response of an animal population to management actions is usually imprecise. In addition, even if a response can be detected, the time lag may be too long to change trajectory within an acceptable timeframe. Imprecise metrics often fail to identify problems until either it is too late to prevent precipitous population declines or rescue would require extraordinary measures. Avoiding such scenarios through early detection of declines should be one of the primary objectives of any monitoring program.

The USFWS Grizzly Bear Recovery Plan (US Fish and Wildlife Service 1993) focuses on monitoring three primary parameters in the NCDE: (1) the number of unduplicated females with cubs observed annually, (2) the distribution of females with dependent offspring, and (3) the number of known, human–caused bear mortalities. The purpose of the first parameter is to generate an estimate of minimum grizzly bear abundance from which allowable human–caused mortality limits can be determined. This method dramatically underestimates abundance and, consequently, to overestimate the annual mortality rate (Kendall et al. 2009). Neither of the first two parameters employs a rigorous sampling design to derive estimates; instead they rely on opportunistic sightings made during routine activities by state and federal management agency personnel. As such, changes in the numbers of family groups detected may be a function of sampling effort rather than true changes within the population. Further, these methods provide no measure of uncertainty (e.g., confidence intervals). In general, these monitoring approaches would not meet contemporary evidentiary standards and are, along with the recovery criteria themselves, currently being revised.

The 1993 Recovery Plan states that, “The development of a population monitoring system requires balance between precision and cost. High precision requires intrusive monitoring of the population at relatively high cost. Low precision usually also is low in cost but produces data with wide, sometimes questionable, confidence. The optimum monitoring system should be repeatable and nonintrusive (it should not require continuous capture and handling of animals). The optimum system should not require exorbitant expense or highly trained and specialized personnel whose time is solely devoted to grizzly bear monitoring.” The Recovery Plan also calls for development of a conservation strategy that will include population monitoring that continues after recovery and delisting. It follows that, ideally, such a monitoring program would be affordable, precise, and not rely on the capture and handling of animals.

Recent research based on the results of the NDGBP and the Greater Glacier National Park Area Project (GGAP; Kendall et al. 2008) suggests that noninvasive genetic sampling (NGS) may satisfy this definition of a desirable monitoring program for grizzlies in the NCDE, both prior to and following delisting. Specifically, genotypes derived from hair samples collected during repeated surveys of naturally–occurring bear rubs appear to yield capture probabilities sufficient to estimate gender–specific growth rates and apparent survival when used with Pradel (1996) temporal symmetry models. Detections made at bear rubs also provide data on bear distribution, regional density patterns, and population genetic characteristics. Bear rub surveys can be conducted entirely on recognized human and animal travel routes, can be performed by personnel with very little training, and do not require any handling of study animals.

Study Area

Project Study Area MapGrizzly bears are present throughout most of the Northern Continental Divide Ecosystem. The study area of the Northern Divide Grizzly Bear Project encompasses 31,409 km2 (7.6 million acres) and extends from the Canadian border to approximately Hwy 200 (right, click on map for larger version). It includes Glacier National Park (NP), parts of five national forests (Flathead, Helena, Kootenai, Lewis and Clark, and Lolo), parts of the Blackfeet and Flathead Indian Reservations, and significant amounts of state and private land. Within the national forest lands are five Wilderness areas (Bob Marshall, Mission Mountains, Rattlesnake, Great Bear, and Scapegoat) and one wilderness study area (Deep Creek North). Officially designated roadless areas comprise 34% of the study area. Ninety nine percent of Glacier NP is roadless and managed as wilderness. With the addition of the park, 50% of the study area is roadless. There are 6,900 km (4,300 mi) of trail in the NCDE. The study area is a region of diverse land use with a central core of rugged mountains managed as national park, wilderness, and multiple-use forest lands surrounded by lower elevation state and corporate timber lands, state game preserves, private ranch lands, and towns. Many agreements have been made between the USGS and the agencies that manage the lands included in the study area. Written permission was also obtained from hundreds of private landowners that have property inside the study area. A significant amount of the study area is private land, therefore it is very important in order for this project to be a success to not only get permission from these landowners to access their land, but also to involve them in the study. Private landowners have intimate knowledge of the presence of and travel routes of grizzly bears on their land.

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Field Methods

All field work within the 7.76 million acre study area is done on foot.


grizzly bear rubbing on a bear rub treeDuring the 2009 field season crews will conduct surveys to locate bear rub objects throughout the study area. Rub objects are found by hiking trails, forest roads, powerlines, and other areas throughout the ecosystem to look for bear hair on trees, posts, power poles, cabins, and other objects that bears rub on. The location of rub objects is entered into a Geographic Information System (GIS) and maps are produced to assist field personnel in locating the rubs during hair collection efforts. Information such as tree species, diameter, and distance from trail are recorded and entered into a database.

Bear rubs are set up in several ways depending on the type of rub. Typically, short pieces of barbed wire are attached to the rub surface. Hair samples deposited on barbed wire are larger, have more follicles, and have higher genotyping success than those found on the natural rub surface. However, when there is evidence that a bear rub is bumped by pack stock, barbless wire is attached vertically to the rub object to prevent damage to packs or injury to horses and riders.

bear hair snaged on barbed wire on a bear rub tree Hair found on each barb is considered a distinct sample. Using tweezers, samples are placed in paper collection envelopes and stored in desiccation chambers.

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Genetic Methods


Genetic analysis can determine the species, gender, and unique identity of a bear using the DNA contained within their hair. Prior to DNA extraction, each hair sample is examined to identify and isolate intact follicles. Acceptable DNA extraction rates are achieved with hair samples with at least two follicles and are the standard for this project. The hair follicles (2-10) are inserted into a solution that breaks down the membrane that surrounds the DNA in the follicle. The samples are then repeatedly "washed" chemically to remove any cellular debris and then stored in a refrigerator until DNA analysis is conducted.


Specific regions (called microsatellites) in the nuclear DNA (n DNA) are amplified (copied) using an optimized polymerase chain reaction (PCR). Electrophoresis is used to separate the DNA segments alongside a standard set of DNA (DNA segments of known length). The length of the amplified DNA segments yields species, unique identity, and gender information.

Data Analysis Methods

Encounter data from bear rub detections will be analyzed using the Pradel (1996) temporal symmetry models in program MARK (White and Burnham 1999). Surveys of a network of bear rubs do not occur instantaneously; therefore multiple detections of each bear will be collapsed into ≥2 secondary occasions for analytical purposes, as in Kendall et al. (2008, 2009) and Boulanger et al. (2008). Multiple, competing models will be developed a priori; relative model support will be assessed with the sample–size adjusted Akaike Information Criteria (AICc; Burnham and Anderson 1998). Models with the lowest AICc scores are considered to have the greatest support based on the data. All models are weighted based on their AICc values, and parameter estimates averaged across models to account for model selection uncertainty. Program RELEASE (Burnham et al. 1987) can be used to test for goodness–of–fit and overdispersion parameters using the recapture portion of the data with the Cormack–Jolly–Seber model (Boulanger et al. 2004). If overdispersion is detected, quasi-AICc (QAICc) methods for model selection and averaging will be used. We will also investigate incorporating data from multiple sources into all analyses (e.g., mortality data; sensu Boulanger et al. 2008), and will use individual, group, and temporal covariates to improve estimate precision and minimize bias.

    • Boulanger, J., S. Himmer, and C. Swan. 2004. Monitoring of grizzly bear population trends and demography using DNA mark-recapture methods in the Owikeno Lake area of British Columbia. Canadian Journal of Zoology 82:1267–1277.
    • Boulanger, J., K.C. Kendall, J.B. Stetz, D.A. Roon, L.P. Waits, and D. Paetkau. 2008. Use of multiple data sources to improve DNA–based mark–recapture population estimates of grizzly bears. Ecological Applications 18:577–589.
    • Burnham, K.P. and D.R. Anderson. 1998. Model selection and inference: A practical information theoretic approach. Springer. New York. 353 p.
    • Burnham, K.P., D.R. Anderson, G.C. White, C. Brownie, and K.H. Pollock. 1987. Design and analysis methods for fish survival experiments based on release–recapture. American Fisheries Society Monograph No. 5.
    • Kendall, K.C., J.B. Stetz, J. Boulanger, A.C. Macleod, D. Paetkau, and G.C. White. 2009. Demography and genetic structure of a recovering grizzly bear population. Journal of Wildlife Management 73:3–17.
    • Kendall, K.C., J.B. Stetz, D.A. Roon, L.P. Waits, J.B. Boulanger, and D. Paetkau. 2008. Grizzly Bear Density in Glacier National Park, Montana. Journal of Wildlife Management 72:1693-1705.
    • Pradel, R. 1996. Utilization of capture–mark–recapture for the study of recruitment and population growth rate. Biometrics 52:703–709.
    • White, G.C. and K.P. Burnham. 1999. Program MARK: Survival estimation from populations of marked animals. Bird Study Supplement 46:120–138


Field Results: No results at this time. Fieldwork begins May 2009

Genetic Analysis: No results at this time.

Data/Statistical Analysis: No results at this time.

Related Publications


Related Materials

Related Projects

  • Northern Divide Bear Project (2003-2008):
  • Greater Glacier Bear DNA Project (1997-2002): project website
  • Use of Remote Camera Systems: Remote video and still cameras were used to: investigate how grizzly bears, black bears, and other wildlife species respond to baited, barbed wire hair traps; bear use of naturally-occurring bear rubs, bear marking behavior, and effects of putting barbed wire on bear rubs to facilitate hair collection; how hair traps may be modified to improve detection probabilities. Use of remote camera systems to investigate efficiency of DNA-based sampling methods


grizzly bear, black bear, DNA finger printing, mark-recapture, wildlife, population, landscape scale, non-invasive sampling, conservation genetics, hair, microsatellites, polymerase chain reaction, Ursus arctos, Ursus americanus, hair snag, sign survey, genetics, Glacier National Park, Blackfoot Nation, Flathead National Forest, Helena National Forest, Kootenai National Forest, Lewis and Clark National Forest, Lolo National Forest, Bob Marshall Wilderness, Mission Mountains, Great Bear Wilderness, Scapegoat Wilderness, Northern Continental Divide Ecosystem

Geographic Distribution

Northern Continental Divide Ecosystem, Northwest Montana

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Also visit the National Park Service's Glacier National Park official website to learn more about park activities.