Interagency Grizzly Bear Study Team Active
The Interagency Grizzly Bear Study Team (IGBST) is an interdisciplinary group of scientists and biologists responsible for long-term monitoring and research efforts on grizzly bears in the Greater Yellowstone Ecosystem (GYE). The team was formed by the Department of the Interior (DOI) in 1973 as a direct result of controversy surrounding the closure of open pit garbage dumps within Yellowstone National Park during 1968-72. IGBST members are representatives from the U.S. Geological Survey, National Park Service, U.S. Fish and Wildlife Service, U.S. Forest Service, the Eastern Shoshone and Northern Arapaho Tribal Fish and Game Department, and the States of Idaho, Montana, and Wyoming. This interagency approach ensures consistency in data collection and allows for combining limited resources to address information needs throughout the GYE.
The IGBST Leader serves as a technical and science advisor to the Interagency Grizzly Bear Committee and its Yellowstone Ecosystem Subcommittee, but is not a voting member of the committees.
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:
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.
Below are other science projects associated with this project.
The IGBST has been capturing and radiocollaring grizzly bears since 1975. Data collected from marked bears provide the information necessary for tracking key population parameters. This gallery shows the process by which we capture and collar grizzly bears for research purposes. All research animals are handled by following the specific requirements of USGS Animal Care and Use policies.
Animated image showing grizzly bear range expansion in GYE: 1990-2022
Sequential estimates of occupied ranges for grizzly bears in the Greater Yellowstone Ecosystem during 1990–2022 (Dellinger et al. 2023). Range extents are based on methods described in Bjornlie et al. (2014).
IGBST Complete Publications 1974 - 2020
Roadside bear viewing opportunities in Yellowstone National Park: characteristics, trends, and influence of whitebark pine
Influence of whitebark pine decline on fall habitat use and movements of grizzly bears in the Greater Yellowstone Ecosystem
Re-evaluation of Yellowstone grizzly bear population dynamics not supported by empirical data: response to Doak & Cutler
Methods to estimate distribution and range extent of grizzly bears in the Greater Yellowstone Ecosystem
Contrasting past and current numbers of bears visiting Yellowstone cutthroat trout streams
Dietary breadth of grizzly bears in the Greater Yellowstone Ecosystem
Response of Yellowstone grizzly bears to changes in food resources: A synthesis. Final report to the Interagency Grizzly Bear Committee and Yellowstone Ecosystem Subcommittee
Insights into the latent multinomial model through mark-resight data on female grizzly bears with cubs-of-the-year
Effects of sampling conditions on DNA-based estimates of American black bear abundance
Omnivory and the terrestrial food web: Yellowstone grizzly beard diets
Body and diet composition of sympatric black and grizzly bears in the Greater Yellowstone Ecosystem
Stable isotopes to detect food-conditioned bears and to evaluate human-bear management
Current grizzly bear mortality tables are located on the Interagency Grizzly Bear Study Team main page (Overview tab) under the "Grizzly Bear Mortality Information" section
Below are news stories associated with this project.
In a changing ecosystem, Yellowstone grizzly bears are resilient
BOZEMAN, Mont. — Grizzly bears in the Greater Yellowstone Ecosystem have been able to gain the body fat they need for hibernation even as population densities have increased and as climate change and human impacts have changed the availability of some foods, according to a new study by the U.S. Geological Survey and its partners.
Below are partners associated with this project.
- Overview
The Interagency Grizzly Bear Study Team (IGBST) is an interdisciplinary group of scientists and biologists responsible for long-term monitoring and research efforts on grizzly bears in the Greater Yellowstone Ecosystem (GYE). The team was formed by the Department of the Interior (DOI) in 1973 as a direct result of controversy surrounding the closure of open pit garbage dumps within Yellowstone National Park during 1968-72. IGBST members are representatives from the U.S. Geological Survey, National Park Service, U.S. Fish and Wildlife Service, U.S. Forest Service, the Eastern Shoshone and Northern Arapaho Tribal Fish and Game Department, and the States of Idaho, Montana, and Wyoming. This interagency approach ensures consistency in data collection and allows for combining limited resources to address information needs throughout the GYE.
The IGBST Leader serves as a technical and science advisor to the Interagency Grizzly Bear Committee and its Yellowstone Ecosystem Subcommittee, but is not a voting member of the committees.
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.
Sources/Usage: Some content may have restrictions. View Media DetailsUnique 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:
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.
- Science
Below are other science projects associated with this project.
- Multimedia
The IGBST has been capturing and radiocollaring grizzly bears since 1975. Data collected from marked bears provide the information necessary for tracking key population parameters. This gallery shows the process by which we capture and collar grizzly bears for research purposes. All research animals are handled by following the specific requirements of USGS Animal Care and Use policies.
Animated image showing grizzly bear range expansion in GYE: 1990-2022
Sequential estimates of occupied ranges for grizzly bears in the Greater Yellowstone Ecosystem during 1990–2022 (Dellinger et al. 2023). Range extents are based on methods described in Bjornlie et al. (2014).
- Publications
IGBST Complete Publications 1974 - 2020
Filter Total Items: 84Roadside bear viewing opportunities in Yellowstone National Park: characteristics, trends, and influence of whitebark pine
Opportunities for viewing grizzly bears (Ursus arctos) and American black bears (U. americanus) from roadways in Yellowstone National Park (YNP) have increased in recent years. Unlike the panhandling bears common prior to the 1970s, current viewing usually involves bears feeding on natural foods. We define roadside bear viewing opportunities that cause traffic congestion as ‘‘bear-jams.’’ We invesAuthorsMark A. Haroldson, Kerry GuntherInfluence of whitebark pine decline on fall habitat use and movements of grizzly bears in the Greater Yellowstone Ecosystem
When abundant, seeds of the high-elevation whitebark pine (WBP; Pinus albicaulis) are an important fall food for grizzly bears (Ursus arctos) in the Greater Yellowstone Ecosystem. Rates of bear mortality and bear/human conflicts have been inversely associated with WBP productivity. Recently, mountain pine beetles (Dendroctonus ponderosae) have killed many cone-producing WBP trees. We used fall (15AuthorsCecily M. Costello, Frank T. van Manen, Mark A. Haroldson, Michael R. Ebinger, Steven L. Cain, Kerry A. Gunther, Daniel D. BjornlieRe-evaluation of Yellowstone grizzly bear population dynamics not supported by empirical data: response to Doak & Cutler
Doak and Cutler critiqued methods used by the Interagency Grizzly Bear Study Team (IGBST) to estimate grizzly bear population size and trend in the Greater Yellowstone Ecosystem. Here, we focus on the premise, implementation, and interpretation of simulations they used to support their arguments. They argued that population increases documented by IGBST based on females with cubs-of-the-year wereAuthorsFrank T. van Manen, Michael R. Ebinger, Mark A. Haroldson, Richard B. Harris, Megan D. Higgs, Steve Cherry, Gary C. White, Charles C. SchwartzMethods to estimate distribution and range extent of grizzly bears in the Greater Yellowstone Ecosystem
The distribution of the Greater Yellowstone Ecosystem grizzly bear (Ursus arctos) population has expanded into areas unoccupied since the early 20th century. Up-to-date information on the area and extent of this distribution is crucial for federal, state, and tribal wildlife and land managers to make informed decisions regarding grizzly bear management. The most recent estimate of grizzly bear disAuthorsMark A. Haroldson, Charles C. Schwartz, Daniel J. Thompson, Daniel D. Bjornlie, Kerry A. Gunther, Steven L. Cain, Daniel B. Tyers, Kevin L. Frey, Bryan C. AberContrasting past and current numbers of bears visiting Yellowstone cutthroat trout streams
Spawning cutthroat trout (Oncorhynchus clarkii bouvieri) were historically abundant within tributary streams of Yellowstone Lake within Yellowstone National Park and were a highly digestible source of energy and protein for Yellowstone’s grizzly bears (Ursus arctos) and black bears (U. americanus). The cutthroat trout population has subsequently declined since the introduction of non-native lake tAuthorsMark A. Haroldson, Charles C. Schwartz, Justin E. Teisberg, Kerry A. Gunther, Jennifer K. Fortin, Charles T. RobbinsDietary breadth of grizzly bears in the Greater Yellowstone Ecosystem
Grizzly bears (Ursus arctos) in the Greater Yellowstone Ecosystem (GYE) are opportunistic omnivores that eat a great diversity of plant and animal species. Changes in climate may affect regional vegetation, hydrology, insects, and fire regimes, likely influencing the abundance, range, and elevational distribution of the plants and animals consumed by GYE grizzly bears. Determining the dietary breaAuthorsKerry A. Gunther, Rebecca Shoemaker, Kevin L. Frey, Mark A. Haroldson, Steven L. Cain, Frank T. van Manen, Jennifer K. FortinResponse of Yellowstone grizzly bears to changes in food resources: A synthesis. Final report to the Interagency Grizzly Bear Committee and Yellowstone Ecosystem Subcommittee
The Yellowstone grizzly bear (Ursus arctos) was listed as a threatened species in 1975 (Federal Register 40 FR:31734-31736). Since listing, recovery efforts have focused on increasing population size, improving habitat security, managing bear mortalities, and reducing bear-human conflicts. The Interagency Grizzly Bear Committee (IGBC; partnership of federal and state agencies responsible for grizzAuthorsFrank T. van Manen, Cecily M. Costello, Mark A. Haroldson, Daniel D. Bjornlie, Michael R. Ebinger, Kerry A. Gunther, Mary Frances Mahalovich, Daniel J. Thompson, Megan D. Higgs, Kathryn M. Irvine, Kristin Legg, Daniel B. Tyers, Lisa Landenburger, Steven L. Cain, Kevin L. Frey, Bryan C. Aber, Charles C. SchwartzInsights into the latent multinomial model through mark-resight data on female grizzly bears with cubs-of-the-year
Mark-resight designs for estimation of population abundance are common and attractive to researchers. However, inference from such designs is very limited when faced with sparse data, either from a low number of marked animals, a low probability of detection, or both. In the Greater Yellowstone Ecosystem, yearly mark-resight data are collected for female grizzly bears with cubs-of-the-year (FCOY),AuthorsMegan D. Higgs, William A. Link, Gary C. White, Mark A. Haroldson, Daniel D. BjornlieEffects of sampling conditions on DNA-based estimates of American black bear abundance
DNA-based capture-mark-recapture techniques are commonly used to estimate American black bear (Ursus americanus) population abundance (N). Although the technique is well established, many questions remain regarding study design. In particular, relationships among N, capture probability of heterogeneity mixtures A and B (pA and pB, respectively, or p, collectively), the proportion of each mixture (AuthorsJared S. Laufenberg, Frank T. van Manen, Joseph D. ClarkOmnivory and the terrestrial food web: Yellowstone grizzly beard diets
No abstract available.AuthorsCharles C. Schwartz, Mark A. Haroldson, Kerry A. Gunther, Charles T. RobbinsBody and diet composition of sympatric black and grizzly bears in the Greater Yellowstone Ecosystem
The Greater Yellowstone Ecosystem (GYE) has experienced changes in the distribution and availability of grizzly bear (Ursus arctos) food resources in recent decades. The decline of ungulates, fish, and whitebark pine seeds (Pinus albicaulis) has prompted questions regarding their ability to adapt. We examined body composition and diet of grizzly bears using bioelectrical impedance and stable isotoAuthorsCharles C. Schwartz, Jennifer K. Fortin, Justin E. Teisberg, Mark A. Haroldson, Christopher Servheen, Charles T. Robbins, Frank T. van ManenStable isotopes to detect food-conditioned bears and to evaluate human-bear management
We used genetic and stable isotope analysis of hair from free-ranging black bears (Ursus americanus) in Yosemite National Park, California, USA to: 1) identify bears that consume human food, 2) estimate the diets of these bears, and 3) evaluate the Yosemite human–bear management program. Specifically, we analyzed the isotopic composition of hair from bears known a priori to be food-conditioned orAuthorsJohn B. Hopkins, Paul L. Koch, Charles C. Schwartz, Jake M. Ferguson, Schuyler S. Greenleaf, Steven T. Kalinowski - Web Tools
Current grizzly bear mortality tables are located on the Interagency Grizzly Bear Study Team main page (Overview tab) under the "Grizzly Bear Mortality Information" section
- News
Below are news stories associated with this project.
In a changing ecosystem, Yellowstone grizzly bears are resilient
BOZEMAN, Mont. — Grizzly bears in the Greater Yellowstone Ecosystem have been able to gain the body fat they need for hibernation even as population densities have increased and as climate change and human impacts have changed the availability of some foods, according to a new study by the U.S. Geological Survey and its partners.
- Partners
Below are partners associated with this project.