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: 1990-2020
Sequential estimates of occupied ranges for grizzly bears in the Greater Yellowstone Ecosystem during 1990–2020. Range extents are based on methods described in Bjornlie et al. (2014).
IGBST Complete Publications 1974 - 2020
Temporal, spatial, and environmental influences on the demographics of grizzly bears in the Greater Yellowstone Ecosystem
Distribution of grizzly bears in the Greater Yellowstone Ecosystem, 2004
Assessment of pesticide residues in army cutworm moths (Euxoa auxiliaris) from the Greater Yellowstone Ecosystem and their potential consequences to foraging grizzly bears (Ursus arctos horribilis)
Grizzly bear nutrition and ecology studies in Yellowstone National Park
Yellowstone grizzly bear investigations: Annual report of the Interagency Grizzly Bear Study Team, 2004
Consumption of pondweed rhizomes by Yellowstone grizzly bears
Changing numbers of spawning cutthroat trout in tributary streams of Yellowstone Lake and estimates of grizzly bears visiting streams from DNA
Yellowstone grizzly bear investigations: Annual report of the Interagency Grizzly Bear Study Team, 2003
Possible effects of elk harvest on fall distribution of grizzly bears in the Greater Yellowstone Ecosystem
Importance of salmon to wildlife: Implications for integrated management
Modeling survival: application of the Andersen-Gill model to Yellowstone grizzly bears
Carnivore re-colonisation: Reality, possibility and a non-equilibrium century for grizzly bears in the southern Yellowstone ecosystem
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: 1990-2020
Sequential estimates of occupied ranges for grizzly bears in the Greater Yellowstone Ecosystem during 1990–2020. Range extents are based on methods described in Bjornlie et al. (2014).
- Publications
IGBST Complete Publications 1974 - 2020
Filter Total Items: 84Temporal, spatial, and environmental influences on the demographics of grizzly bears in the Greater Yellowstone Ecosystem
During the past 2 decades, the grizzly bear (Ursus arctos) population in the Greater Yellowstone Ecosystem (GYE) has increased in numbers and expanded in range. Understanding temporal, environmental, and spatial variables responsible for this change is useful in evaluating what likely influenced grizzly bear demographics in the GYE and where future management efforts might benefit conservation andAuthorsCharles C. Schwartz, Mark A. Haroldson, Gary C. White, Richard B. Harris, Steve Cherry, Kim A. Keating, Dave Moody, Christopher ServheenDistribution of grizzly bears in the Greater Yellowstone Ecosystem, 2004
The US Fish and Wildlife Service (USFWS) proposed delisting the Yellowstone grizzly bear (Ursus arctos horribilis) in November 2005. Part of that process required knowledge of the most current distribution of the species. Here, we update an earlier estimate of occupied range (1990–2000) with data through 2004. We used kernel estimators to develop distribution maps of occupied habitats based on iniAuthorsC.C. Schwartz, M.A. Haroldson, K. Gunther, D. MoodyAssessment of pesticide residues in army cutworm moths (Euxoa auxiliaris) from the Greater Yellowstone Ecosystem and their potential consequences to foraging grizzly bears (Ursus arctos horribilis)
During summer, a grizzly bear (Ursus arctos horribilis) in the Greater Yellowstone Ecosystem (GYE) (USA) can excavate and consume millions of army cutworm moths (Euxoa auxiliaris) (ACMs) that aggregate in high elevation talus. Grizzly bears in the GYE were listed as threatened by the US Fish and Wildlife Service in 1975 and were proposed for delisting in 2005. However, questions remain about key bAuthorsH. L. Robison, Charles C. Schwartz, J. D. Petty, P. F. BrussardGrizzly bear nutrition and ecology studies in Yellowstone National Park
T HE CHANCE TO SEE a wild grizzly bear is often the first or second reason people give for visiting Yellow - stone National Park. Public interest in bears is closely coupled with a desire to perpetuate this wild symbol of the American West. Grizzly bears have long been described as a wilderness species requiring large tracts of undisturbed habitat. However, in today’s world, most grizzly bears livAuthorsCharles T. Robbins, Charles C. Schwartz, Kerry A. Gunther, Christopher ServheenYellowstone grizzly bear investigations: Annual report of the Interagency Grizzly Bear Study Team, 2004
The contents of this Annual Report summarize results of monitoring and research from the 2004 field season. The report also contains a summary of nuisance grizzly bear (Ursus arctos horribilis) management actions. The study team continues to work on issues associated with counts of unduplicated females with cubs-of-the-year (COY). These counts are used to establish a minimum population size, whichConsumption of pondweed rhizomes by Yellowstone grizzly bears
Pondweeds (Potamogeton spp.) are common foods of waterfowl throughout the Northern Hemisphere. However, consumption of pondweeds by bears has been noted only once, in Russia. We documented consumption of pondweed rhizomes by grizzly bears (Ursus arctos) in the Yellowstone region, 1977-96, during investigations of telemetry locations obtained from 175 radiomarked bears. We documented pondweed excavAuthorsD.J. Mattson, S.R. Podruzny, M.A. HaroldsonChanging numbers of spawning cutthroat trout in tributary streams of Yellowstone Lake and estimates of grizzly bears visiting streams from DNA
Spawning Yellowstone cutthroat trout (Oncorhynchus clarki) provide a source of highly digestible energy for grizzly bears (Ursus arctos) that visit tributary streams to Yellowstone Lake during the spring and early summer. During 1985–87, research documented grizzly bears fishing on 61% of the 124 tributary streams to the lake. Using track measurements, it was estimated that a minimum of 44 grizzlyAuthorsM.A. Haroldson, K.A. Gunther, Daniel P. Reinhart, S.R. Podruzny, C. Cegelski, L. Waits, T.C. Wyman, J. SmithYellowstone grizzly bear investigations: Annual report of the Interagency Grizzly Bear Study Team, 2003
The contents of this Annual Report summarize results of monitoring and research from the 2003 field season. The report also contains a summary of nuisance grizzly bear (Ursus arctos horribilis) management actions. The study team continues to work on issues associated with counts of unduplicated females with cubs-of-the-year (COY). These counts are used to establish a minimum population size, whichPossible effects of elk harvest on fall distribution of grizzly bears in the Greater Yellowstone Ecosystem
The tradition of early elk (Cervus elaphus) hunting seasons adjacent to Yellowstone National Park (YNP), USA, provides grizzly bears (Ursus arctos horribilis) with ungulate remains left by hunters. We investigated the fall (Aug–Oct) distribution of grizzly bears relative to the boundaries of YNP and the opening of September elk hunting seasons. Based on results from exact tests of conditional indAuthorsM.A. Haroldson, C.C. Schwartz, S. Cherry, D. MoodyImportance of salmon to wildlife: Implications for integrated management
Salmon (Oncorhynchuss pp.) are an important resource for terrestrial wildlife. However, the salmon requirements of wildlife populations and the role wildlife play in nutrient transport across ecosystems are largely ignored in salmon and habitat management. Any activity that reduces the availability of or access to salmon by wildlife may adversely affect wildlife populations and, potentially, ecosyAuthorsGrant V. Hilderbrand, Sean D. Farley, Charles C. Schwartz, Charles T. RobbinsModeling survival: application of the Andersen-Gill model to Yellowstone grizzly bears
Wildlife ecologists often use the Kaplan-Meier procedure or Cox proportional hazards model to estimate survival rates, distributions, and magnitude of risk factors. The Andersen-Gill formulation (A-G) of the Cox proportional hazards model has seen limited application to mark-resight data but has a number of advantages, including the ability to accommodate left-censored data, time-varying covariatAuthorsChristopher J. Johnson, Mark S. Boyce, Charles C. Schwartz, Mark A. HaroldsonCarnivore re-colonisation: Reality, possibility and a non-equilibrium century for grizzly bears in the southern Yellowstone ecosystem
Most large native carnivores have experienced range contractions due to conflicts with humans, although neither rates of spatial collapse nor expansion have been well characterised. In North America, the grizzly bear (Ursus arctos) once ranged from Mexico northward to Alaska, however its range in the continental USA has been reduced by 95-98%. Under the U. S. Endangered Species Act, the YellowstonAuthorsSanjay Pyare, S. Cain, D. Moody, C. Schwartz, J. Berger - 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.