Interagency Grizzly Bear Study Team Active

The main objectives of the team are to 1) monitor the status and trend of the grizzly bear population in the GYE and 2) determine patterns of habitat use by bears and the relationship of land management activities to the welfare of the bear population. To meet these objectives, the team focuses on three main research areas.

Unique Females with Cubs-of-the-Year  

Adult females are the most important demographic segment of the grizzly bear populations because they are the reproductive engine.  Adult females with cubs-of-the-year (cubs) are the most easily and reliably recognized cohort of grizzly bear populations.  Consequently females with cubs are a major focus of IGBST’s monitoring program in the Greater Yellowstone Ecosystem (GYE).  Tracking trend for this segment of the population is generally representative of the trend for entire population.  Thus, if we observe growth in numbers of female with cubs, we can be reasonably sure the entire population is growing.  Efforts by IGBST to document the abundance and distribution of females with cubs began in 1973 and have improved over time by implementing standardized protocols and new statistical procedures.  During the past 10 years (2006-2015), IGBST has estimated an average of 56 unique females with cubs annually. When combined with other data, these estimates serve as the basis for estimating total population size.  Estimates of total population size are used by IGBST to evaluate annual mortality and to assess whether mortality is sustainable.  Sustainable mortality establishes a limit on the number of grizzly deaths that can occur given population objectives.  Information from these studies is crucial to evaluate trends in the grizzly bear population and assess the long-term health of the population.

Radio-Collaring Bears

IGBST began radiocollaring grizzly bears in the Greater Yellowstone Ecosystem (GYE) in 1975.  Since then, we have radio-monitored over 830 individuals for varying durations, typically for 2 to 3 years.  Over 100 individuals have been monitored during more than 5 different years.  Our monitoring program changed in 1986 based on directions from the Interagency Grizzly Bear Committee’s Population Task Force.  They recommended we maintain and monitor a minimum of 25 radio-collared adult females annually.  We also use telemetry to monitor a representative sample of adult males.  Data collected from radio-marked bears provide information necessary for tracking key population parameters.  By observing radio-collared bears, we document age of first reproduction, average litter size, cub and yearling survival, how often a female produces a litter, and causes of mortality.  These data allow us to estimate survival among different sex and age classes of bears.  Collectively, this is referred to as “known-fate monitoring”.  In conjunction with other estimates (i.e., number of females with cubs, annual mortality), this information is used estimate population size and evaluate sustainable mortality.  Location information obtained from collared bears also provides reliable data that helps resource managers focus their activities toward landscape issues that impact grizzly bears in the GYE.

All research animals are handled by following the specific requirements of USGS Animal Care and Use policies.

Whitebark Pine Monitoring

Whitebark pine seeds are a high-calorie food resource available to grizzly bears during late summer and fall.  Because whitebark pine is a masting species, cone production is variable, with good crops every 2 to 3 years.  Whitebark pine seeds are high in fats and proteins and, when available, allow grizzly bears to build up fat reserves during fall in preparation for hibernation.  Grizzly bears harvest these cones by raiding seed caches of red squirrels (middens).  Since 1980, we have annually monitored whitebark pine cone production throughout the Greater Yellowstone Ecosystem (GYE) using surveys of established transects. Our data show that mature, cone-producing whitebark pine trees in the GYE have experienced substantial mortality, primarily due to a mountain pine beetle outbreak that started in the early 2000s, but also from white pine blister rust, and fire.  IGBST research shows that grizzly bears are adapting to these changes by shifting their diets (see Food Synthesis Report).  However, we will continue to monitor this food resource because bears still make extensive use of it in years of good cone production.  Click here for IGBST Whitebark Pine Cone Production Annual Summaries.

FOR INFORMATION ABOUT GRIZZLY BEAR MORTALITY, SEE BOTTOM OF PAGE (below "Reports" section).

Direct Links:

IGBST Annual Reports

IGBST Boundary Maps

IGBST GIS Data Download

Grizzly Bear Mortality Information (See "Grizzly Bear Mortality Information" near bottom of page)

Bear Caused Human Fatalities in the GYE, 1892 - Present

IGBST Grizzly Bear Food Synthesis Report

IGBST Whitebark Pine Cone Production Annual Summaries

Animated image showing grizzly bear range expansion in GYE: 1990-2020

Reports:

A Reassessment of Chao2 Estimates for Population Monitoring of Grizzly

IGBST Demographic Workshop Report

GRIZZLY BEAR MORTALITY INFORMATION:

Identifying the locations and causes of grizzly bear mortality is a key component in understanding the dynamics of this population. About 85% of all documented bear mortalities are human-caused. Tracking human-caused bear deaths helps define patterns and trends that can direct management programs designed to reduce bear mortality.

1) Documented known and probable grizzly bear mortalities in the Greater Yellowstone Ecosystem for 2022 can be found in a provisional USGS data release that is updated as grizzly bear mortalities are reported by IGBST member agencies throughout the year. Go to “Attached Files” and download the “GB_Mortality_2022 csv” file, which contains a table with all reported mortalities for the current year.

Important notice: Because the current year’s grizzly bear mortality data are continuously updated and thus subject to revision, they are considered preliminary data by the USGS. Therefore, if these data are used for any purpose, please refer to them as preliminary data (see full data disclaimer under the “Summary” section of the provisional data release). At the end of the calendar year, these data will be compiled, undergo additional review, and added to the existing data release listed below, which contains documented mortality data compiled by the IGBST since 2015. Once the current year’s data are added to the existing data release, they are no longer considered provisional, which will be reflected on this website.

2) Documented known and probable grizzly bear mortalities in the Greater Yellowstone Ecosystem during 2015-2021 can be found in a USGS data release.

3) 2009-2014 grizzly bear mortality tables can be found in IGBST Annual Reports of the same years.