Shorts - Part One
From Yellowstone Science 23(2): 2015, pages 49-61.
Grizzly Bears and Army Cutworm Moths
Dan D. Bjornlie & Mark A. Haroldson
Grizzly bears in the Greater Yellowstone Ecosystem (GYE) have a very diverse menu, consisting of items many people would expect to see on their "dinner plate"—items like meat, fish, berries, and the occasional unsecured picnic basket. Moths are not likely one of those expected menu items.However, for more than 200 grizzly bears in the Absaroka Mountains of Wyoming, east of Yellowstone National Park, moths are a bountiful source of calories.
Although grizzly bear use of army cutworm moth (Euxoa auxiliaris) sites was documented in northwestern Montana in the mid-1950s, it was relatively unknown to scientists studying Yellowstone grizzly bears until the 1980s. There had been undocumented reports of grizzly bears eating "bugs," "insects," or "moths;" but it was not until 1986 that a radio-collared grizzly bear was observed feeding on moths in the GYE (French et al. 1994).
Army cutworm moths do not reside in the Absaroka Mountains year-round;in early summer, they migrate long distances to these alpine areas from the agricultural fields of the Great Plains. Once in the mountains, they feed on the nectar of alpine flowers by night and hide out in the interstitial spaces of the rocky talus slopes by day.These slopes are typically at or above 3,200 meters (10,500 feet) in elevation. It is on these high-elevation talus slopes that grizzly bears seek out army cutworm moths. By moving rocks and licking up the fast-moving moths before they can escape into another hole between rocks, bears can consume from 40,000 to 60,000 moths in a single day (White et al. 1999). At 8 kilocalories per gram, army cutworm moths are the richest documented food available to grizzly bears in the GYE (French et al. 1994). Remarkably, this level of moth consumption can supply a typical grizzly bear with approximately one-half of its annual caloric requirements in a 30-day period (White et al. 1999).
The abundance of moths, their high caloric value, and their ubiquitous dispersal within sites, make grizzly bears feeding at moth sites generally tolerant of other bears;they can be found feeding in groups of a dozen or more (French et al. 1994, Robison 2009). This is similar to bears feeding on the salmon streams of Alaska, where abundant food decreases the "personal space" requirements of bears (Smith et al. 2005). Because these talus slopes are generally remote from human development, foraging on moths keeps grizzly bears away from most human activities in summer, thereby reducing the potential for human-bear conflicts in these areas.
In agricultural areas in the Great Plains, army cutworm moths are considered an agricultural nuisance, and pesticides are used to control their numbers. Concerns have been raised about the potential for bioaccumulation of pesticides in bears feeding on moths. However, tests conducted on moths collected at moth aggregation sites where grizzly bears feed found little to no pesticide residue, likely due to moths amassing most of their summer body fat in the alpine tundra where pesticides are not used (Robison 2009).
Army cutworm moths can be found in talus slopes of the Rocky Mountains from New Mexico to Canada and in sites throughout the GYE, including the Teton Range, Wind River Mountains, and Gallatin Range. Why grizzly bears have only been documented feeding on army cutworm moths in the Absaroka Mountains east of Yellowstone Park remains unclear. Perhaps it is due to the juxtaposition of alpine flowers and talus slopes (used by moths) in close proximity to areas commonly used by grizzly bears. As the grizzly population has grown both in size (Schwartz et al. 2006, IGBST 2013) and distribution (Bjornlie et al. 2014), the number of moth sites used by bears and the number of bears observed on sites has increased considerably (Bjornlie and Haroldson 2014). During a flight over all moth sites in 2014, 220 unique grizzly bears were observed feeding on sites, including 14 different females with cubs.It is possible that as the grizzly bear population continues to expand, grizzly bears may discover and use moth sites in other portions of the GYE. If they do, the caloric wealth of army cutworm moths could provide grizzly bears in these new areas with yet another rich food source to maintain a healthy grizzly population.
Bjornlie, D., and M.A. Haroldson. 2014. Grizzly bear use of insect aggregation sites documented from aerial telemetry and observations. Pages 40-43 in F.T. van Manen, M.A. Haroldson, K. West, and S.C. Soileau, editors. Yellowstone grizzly bear investigations: annual report of the Interagency Grizzly Bear Study Team, 2013.U.S. Geological Survey, Bozeman, Montana, USA.
Bjornlie, D.D., D.J. Thompson, M.A. Haroldson, C.C. Schwartz, K.A. Gunther, S.L. Cain, D.B. Tyers, K.L. Frey, and B.C. Aber. 2014. Methods to estimate distribution and range extent of grizzly bears in the Greater Yellowstone Ecosystem. Wildlife Society Bulletin 38:182-187.
French, S.P., M.G. French, and R.R. Knight. 1994. Grizzly bear use of army cutworm moths in the Yellowstone Ecosystem. International Conference on Bear Research and Management 9:389-399.
Interagency Grizzly Bear Study Team (IGBST). 2013. Response of Yellowstone grizzly bears to changes in food resources: A synthesis. Report to the Interagency Grizzly Bear Committee and Yellowstone Ecosystem Subcommittee. Interagency Grizzly Bear Study Team, U.S. Geological Survey, Northern Rocky Mountain Science Center, Bozeman, Montana, USA.
Robison, H.L. 2009. Relationships between army cutworm moths and grizzly bear conservation. Dissertation. University of Nevada-Reno, Reno, Nevada, USA.
Schwartz, C.C., M.A. Haroldson, G.C. White, R.B. Harris, S. Cherry, K.A. Keating, D. Moody, and C. Servheen. 2006. Temporal, spatial, and environmental influences on the demographics of grizzly bears in the Greater Yellowstone Ecosystem. Wildlife Monographs 161:1-8.
Smith, T.S., S. Herrero, and T.D. Debruyn. 2005. Alaskan brown bears, humans, and habituation. Ursus 16:1-10.
White Jr., D.D., K.C. Kendall, and H.D. Picton. 1999. Potential energetic effects of mountain climbers on foraging grizzly bears. Wildlife Society Bulletin 27:146-151.
Response of Grizzly Bears to Overnight Backcountry Camping
Tyler H. Coleman, Charles C. Schwartz, Kerry A. Gunther, & Scott Creel
In Yellowstone National Park, visitors can hike and camp in backcountry areas that are considered critical habitat for the survival and recovery of grizzly bears (USFWS 1993), a species currently listed as threatened under the Endangered Species Act. Parkwide backcountry camping is a popular pastime, and camping numbers have continued to average 42,000 user nights per year over the last several decades (National Park Service 2012, I. Kowski pers. comm.). In 1973, Yellowstone developed new backcountry use procedures that included the establishment of designated backcountry campsites. The new system was designed to concentrate overnight use in distinct locations and to provide campers with bear-resistant, food storage solutions. In 1982, the park further restricted use of backcountry areas deemed critical for grizzly bear recovery by establishing Bear Management Areas (BMAs). The BMAs have restricted off-trail travel and/or seasonally restricted camping or hiking in defined areas. The objective of seasonally restricting human use in certain backcountry campsites was to help reduce human-caused bear disturbance and displacement, and to provide unhindered foraging opportunities for bears. However, since the development of the designated backcountry camping program and the BMA program, limited research had been done to determine if bear behavior or movement was altered by human occupancy in backcountry campsites.
Beginning in 2007, a study was designed to determine if Yellowstone's overnight backcountry human recreation activities were affecting grizzly bear movement and behavior patterns (Coleman et al. 2013). Concurrent with other research studies investigating grizzly bear diet and behavior (Fortin et al. 2013, Schwartz et al. 2014, Teisberg et al. 2013), the study investigated bear movements both inside and near BMAs surrounding Yellowstone Lake, between 2007 and 2009. The study used Global Positioning System (GPS) data collected from both bears and humans. Each GPS location was paired with a time to allow for analysis of discrete interactions between bears and people. Data was collected from 12 GPS radio-collared grizzly bears: nine males and three females. In addition, a unique approach was used to capture human location and movement data from 222 overnight backcountry camping groups (private, commercially-outfitted, and Yellowstone administrative users) occurring over 799 backcountry camp user nights. Hiking parties were randomly contacted at trailheads and asked to participate in the study by affixing a GPS unit to their backpack to track their movements. In almost every case, the individual(s) agreed to participate;and the study recovered 100% of the GPS units sent out with backcountry hikers. When combined with the Yellowstone backcountry reservation system, the human GPS data could identify when campsites were occupied and when they were vacant. This information was then paired with the locations of nearby collared bears. A parallel data analysis was also performed that ignored campsite occupancy. This approach helped to determine if the BMA backcountry restrictions were effective; it also underscored what could happen if researchers neglect the analysis of temporal data in human-wildlife disturbance studies.
Finally, the study helped identify specific distances where bears may be displaced from occupied backcountry campsites, which is helpful when creating buffers for future management decisions. Results indicated that grizzly bears strongly avoided areas within 400 meters of occupied backcountry campsites;however, beyond 400 meters their avoidance response lessened. The parallel analyses indicated bears were indeed avoiding the presence of people in backcountry campsites and not campsites themselves. When campsite occupancy was ignored, bears showed a strong attraction to backcountry campsites. This was a useful method to determine the response of the bear and confirm that backcountry campsite restrictions were effective. Campsite occupancy considered with a time-of-day variable may be an important factor;future studies could include a temporal variable for further investigation of this relationship. Results from this study also confirm previous investigations (Jope 1985, Gunther 1990, Kasworm and Manley 1990), where findings indicated bears avoided non-motorized recreational users in remote, backcountry locations. While the study was successful at concluding grizzly bears generally avoid backcountry areas occupied by people, the results could not be used to determine if variables such as habitat type, bear sex and age, recreational use type (e.g., hikers vs. horseback travel), and backcountry party size influenced bear avoidance behavior. Future studies, with a larger sample size, may be able to replicate the methods and evaluate more specific habitat characteristics.
Coleman, T.H., C.C. Schwartz, K.A. Gunther, and S. Creel. 2013. Influence of overnight recreation on grizzly bear movement and behavior in Yellowstone National Park. Ursus 4:101-110.
Fortin, J.K., C.C. Schwartz, K.A. Gunther, J.E. Teisberg, M.A. Haroldson, and C.T. Robbins.2013.Dietary adjustability of grizzly bears and American black bears in Yellowstone National Park.Journal of Wildlife Management 77:270–281.
Gunther, K.A. 1990. Visitor impact on grizzly bear activity in Pelican Valley, Yellowstone National Park. International Conference on Bear Research and Management 8:73–78.
Hopkins, III, J.B., S. Herrero, R.T. Shideler, K.A. Gunther, C.C. Schwartz, and S.T. Kalinowski. 2010. A proposed lexicon of terms and concepts for human-bear management in North America. Ursus 21:154-168.
Jope, K.L. 1985. Implications of grizzly bear habituation to hikers. Wildlife Society Bulletin 13:32–37.
Kasworm, W.F., and T.L. Manley. 1990. Road and trail influences on grizzly bears and black bears in northwest Montana. International Conference on Bear Research and Management 8:79–84.
National Park Service public use statistics office. 2012. Summary report (multiple years), YELL visitation by month/year. https://irma.nps.gov/Stats/.
Schwartz, C.C., J.K. Fortin, J.E. Teisberg, M.A. Haroldson, C. Servheen, C.T. Robbins, and F.T. van Manen. 2014. Body and diet composition of sympatric black and grizzly bears in the Greater Yellowstone Ecosystem. Journal of Wildlife Management 78:68–78.
Teisberg, J.E., M.A. Haroldson, C.C. Schwartz, K.A. Gunther, J.K. Fortin, and C.T. Robbins. 2014. Contrasting past and current numbers of bears visiting Yellowstone cutthroat trout streams. Journal of Wildlife Management 78:369–378.
U.S. Fish and Wildlife Service. 1993. Grizzly bear recovery plan. U.S. Fish and Wildlife Service, Missoula, Montana, USA.
Expansion of Occupied Grizzly Bear Range
Dan D. Bjornlie, Mark A. Haroldson, Dan J. Thompson, Charles C. Schwartz, Kerry A. Gunther, Steven L. Cain, Dan B. Tyers, Kevin L. Frey, & Bryan Aber
When grizzly bears in the Greater Yellowstone Ecosystem (GYE) were first listed as threatened under the Endangered Species Act in 1975, the population consisted of only a few hundred bears. As the population increased, grizzly bears began to reoccupy portions of their former range, so estimating occupied range became an important task for biologists charged with monitoring the population. Beginning in 1973 and continuing through today, the Interagency Grizzly Bear Study Team has recorded confirmed locations of grizzly bears throughout the GYE. These locations have been used to create periodic estimates of occupied grizzly bear range since the early 1980s (Basile 1982, Blanchard 1992, Schwartz et al. 2002, Schwartz et al. 2006). More recently, new techniques were developed that blended elements from previous survey efforts into a more simplified approach that used all forms of confirmed grizzly bear locations (Bjornlie et al. 2014). Using this technique, reanalysis of past location data provided a fresh look at historic grizzly bear range for direct comparison with current results.
Analysis of grizzly bear locations from the early years of recovery in the late 1970s estimated the area of occupied grizzly bear range at approximately 16,000 square kilometers (6,178 square miles). At that time, the population was centered on Yellowstone National Park and a few adjacent areas of remote wilderness on national forests (figure 1). Through the 1980s, the population grew steadily, increasing its range mainly to the south and east in Wyoming, taking in an area of approximately 23,000 square kilometers (8,880 square miles) by 1989 (figure 1). However, in the 1990s expansion of the GYE grizzly bear population truly began to gather momentum as the population increased in numbers (IGBST 2012). Range expansion into the Owl Creek Mountains and the Upper Green River area of Wyoming, and to the northwest into the Madison and Gallatin mountains of Montana, increased the area of grizzly range to more than 33,000 square kilometers (12,741 square miles) by the end of that decade (figure 2). Another 10 years of expansion increased occupied range of grizzly bears in the GYE to over 50,000 square kilometers (19,305 square miles) by 2010 (Bjornlie et al. 2014), a 51% increase from the 1990s. The most recent estimate in 2014 increased the range to over 58,000 square kilometers (22,394 square miles; figure 1). Major areas of expansion in the 2000s occurred to the west in the Centennial Range on the Idaho-Montana border, the Pitchstone Plateau in the southwestern corner of Yellowstone, and across the Gravelly Range to the eastern slopes of the Snowcrest Range in Montana. In areas north of Yellowstone, expansion occurred to the edge of Interstate 90 at the northern reaches of the Absaroka Range and along the eastern extent of the Beartooth Mountains. To the south, grizzly bear range has expanded to the west and south into the northern portions of the Wyoming Range and the Wind River Mountains.
Changes in the availability of some grizzly bear resources (e.g., whitebark pine seeds) have raised questions regarding whether grizzly bears are simply leaving the core of the GYE in search of food.Female bears do not disperse widely like male bears, so female locations can be used to identify the core of a bear population.Sightings of female grizzly bears with cubs in the GYE have increased concurrently with the expansion of the main population, and show no evidence of a decline in the core of the distribution (figure 2).
Perhaps even more notable than the increase in area of grizzly bear range during recent decades are the many confirmed locations of grizzly bears well beyond the boundary of occupied range, some locations as much as 89 kilometers away (55 miles; figure 1). Many of these locations are in places that have not had documented grizzly bear presence in 100 years or more.In recent years, verified grizzly bear photos were taken by remote cameras at black bear bait sites at the southern extent of the Wind River Range south of Lander, Wyoming, and along the eastern front of the Wyoming Range west of Big Piney, Wyoming (figure 1). The farthest southeast of these locations, near South Pass, are closer to the town of Boulder, Colorado, than they are to the most northwesterly confirmed grizzly bear location on the other side of the GYE. These outliers do not necessarily constitute occupied range, but reveal the leading edges of expansion as dispersing grizzly bears search for new areas to call home.
With the expansion of grizzly bears into long-unoccupied areas, there will be some inevitable growing pains. Some grizzly bears are moving into places that have greater human influence than the more remote core of the GYE. In the 1970s approximately 280 square kilometers (108 square miles) of occupied grizzly bear range encompassed private lands, less than 2% of the total area. Today the area of private land is over 9,000 square kilometers (3,475 square miles), over 16% of the total occupied range (figure 3). A consequence of range expansion is the potential for increases in human-bear conflicts and possibly human-caused bear mortality on private lands.Indeed, numbers of documented human-caused grizzly bear mortalities for independent age bears (≥2 years old) on private lands increased from 4 (12% of the annual total) during the decade of the 1970s, to 41 (26% of the annual total) during the 2000s (figure 4). Most (56%) of the private land mortalities since the 1980s have occurred outside the Grizzly Bear Recovery Zone (see figure 3 in "Demographic Changes in Yellowstone's Grizzly Bear Population," this issue).
People living, working, and recreating in these areas of expansion must now consider the presence of grizzly bears in various ways, whether it be in wildlife and land management practices, storage of attractants (e.g., food and scented items) for backcountry users and homeowners, or changes in techniques for hunting ungulates to avoid conflicts with grizzly bears. The arrival of grizzly bears in these areas will create new challenges for wildlife managers, and require new and innovative approaches. The recovery of the GYE grizzly bear population is one of the greatest success stories in wildlife management. As grizzly bears re-establish in places where they have long been absent, the dedicated management that has allowed the population to recover will continue to be important to maintain a place for one of the most iconic species of the American West.
Basile, J.V. 1982. Grizzly bear distribution in the Yellowstone area, 1973–1979. U.S. Forest Service Research Note INT-321, Ogden, Utah, USA.
Bjornlie, D.D., D.J. Thompson, M.A. Haroldson, C.C. Schwartz, K.A. Gunther, S.L. Cain, D.B. Tyers, K.L. Frey, and B.C. Aber. 2014. Methods to estimate distribution and range extent of grizzly bears in the Greater Yellowstone Ecosystem. Wildlife Society Bulletin 38:182–187.
Blanchard, B.M., R.R. Knight, and D.J. Mattson. 1992. Distribution of Yellowstone grizzly bears during the 1980s. American Midland Naturalist 128:332–338.
Interagency Grizzly Bear Study Team. 2012. Updating and evaluating approaches to estimate population size and sustainable mortality limits for grizzly bears in the Greater Yellowstone Ecosystem. Interagency Grizzly Bear Study Team, U.S. Geological Survey, Northern Rocky Mountain Science Center, Bozeman, Montana, USA.
Schwartz, C.C., M.A. Haroldson, K.A. Gunther, and D. Moody. 2002. Distribution of grizzly bears in the Greater Yellowstone Ecosystem, 1990-2000. Ursus 13:203–212.
Schwartz, C.C., M.A. Haroldson, K.A. Gunther, and D. Moody. 2006. Distribution of grizzly bears in the Greater Yellowstone Ecosystem in 2004. Ursus 17:63–66.
Figure 1. Grizzly bear distribution in the GYE from the 1980s through 2014.
Figure 2. Distributions of initial sightings of unique females with cubs in the GYE from 1976 to 2014.
Figure 3. The area of private lands within grizzly bear distribution in the GYE by decade.
Figure 4. Numbers of documented human-caused mortalities of independent aged grizzly bears (≥2 years old) occurring on private lands in the GYE by decade.
Grizzly Cub Adoptions Confirmed in Yellowstone &Grand Teton National Parks
Mark A. Haroldson, Kerry A. Gunther, Steven L. Cain, Katharine R. Wilmot, &Travis Wyman
The Interagency Grizzly Bear Study Team (IGBST) pays a great deal of attention to sightings of female grizzly bears with cubs (i.e., cubs in their first year of life) in the Greater Yellowstone Ecosystem (GYE). The team collects observations of females with cubs opportunistically from ground-based and aerial observers, and from systematic, twice-yearly observation flights covering over 45,000 km2 in the GYE. The observations collected provide information regarding the distribution of reproductive females, as well as the basis for our population estimates and analyses of trends (Harris et al. 2007). Since team members closely scrutinize these sightings, which often accumulate on a daily basis, we tend to notice when something out of the ordinary happens. For instance, in the spring of 2006, aerial observations of a radio-marked female revealed she was accompanied by a mixed-aged litter of two cubs and one yearling offspring from the previous year (Swenson and Haroldson 2008). Mixed-age litters are rarely observed because females typically do not come into estrus and mate when they are raising cubs. However, if separation of a family occurs, it is possible for the mother to breed, re-associate with her lost offspring, and subsequently produce newborns during the denning period and emerge with a mixed-aged litter. Mixed-age litters might also occur through adoption. Cub adoption is another uncommon occurrence that we recently confirmed on two occasions in the GYE.
During August 2007, we observed an exchange of cubs by two females in the Dunraven Pass-Antelope Creek area of Yellowstone National Park (Haroldson et al. 2008). In this event, an older radio-marked female (#125), that had been observed on multiple occasions with three cubs, was observed with only one cub in mid-August. Shortly thereafter, an unmarked female with two cubs, that had been using roadside habitats in the same area, suddenly appeared with four cubs. Park staff deployed remote cameras and a hair collection site, and were successful in obtaining pictures and hair samples from the unmarked female and the four cubs accompanying her. By extracting DNA from the hair samples and comparing it to our extensive set of genotypes from captured bears, we confirmed that an exchange of cubs between the two mothers had occurred. But the story gets much more interesting. Our analysis also revealed the adult females were mother and daughter, and the father of the adoptive female was an old male grizzly bear (#211) that many park visitors refer to as "Scarface." In addition, this bear was also the father of the cubs that the radio-marked female (#125) lost. Thus, the younger adoptive female had gathered up and cared for her full siblings (one female and one male), as she had the same mother (#125) and father (#211) as the two cubs she took in. Her two cubs by birth were sired by a male (#516), whose home range also included the Antelope Creek area and was also in our genotype database. The young mother was last observed with four cubs during late August 2007. During the spring of 2008, we observed what we believed to be the adoptive female with one yearling on several occasions. Although we cannot be certain, she likely lost all but one of the four cubs.
In July 2011, we documented another exchange of cubs in Grand Teton National Park. Like the previous event, this one involved an adult daughter (#610) and her mother (#399). Both of these bears had been radio-marked in the past, but neither was being actively monitored during 2011. Bear #399 had cast her last radio-collar in August of 2006 when she was accompanied by three cubs, one of which was the future bear #610. Bear #399 was identifiable by her red ear-tag and distinctive scars on the left side of her nose. Her daughter (#610) was initially collared as a 3-year-old in 2009, was given yellow ear tags, and then shed her collar in 2010. DNA samples taken during the capture confirmed her relationship to #399. Both of these females were and continue to be highly visible along park roads and have quite a following among park visitors and wildlife photographers. Both bears were accompanied by cubs during the spring of 2011, #399 with three and #610 with two. Beginning in late July, visitors started reporting a female with yellow ear tags accompanied by three cubs, and a female with a red ear tag with two. These changes in the numbers of cubs per mother caused quite a stir among a group of local photographers, who accused park staff of catching the females and changing their tags and/or mixing up the cubs. We do not know the circumstances surrounding the cub exchange, but park staff and bear researchers had nothing to do with it. None of the bears were captured that year. In October, park staff was successful in obtaining hair samples from the yellow-tagged female and the three cubs with her. Subsequent DNA analyses confirmed the familial relationships;somehow female #610 ended up with one of her mother's (#399) cubs. However, in this event, #610 adopted her half-brother, not a full sibling as in the Yellowstone event described previously;#610's father and the father of her mother's cub that she adopted were different individuals. Both fathers were known to us through our DNA database because they had been previously captured and genotyped. Bear #514 fathered #399's cub adopted by #610, and bear #679 was the father of #610's cubs. We also know female #610 successfully reared her own offspring and her mother's cub to the age of independence, with the break-up of this family occurring in spring of 2013. Bear #399's two remaining cubs stayed with their mother until their second spring, when the family separated a year earlier than is typical, a split that may have been caused by a male bear attempting to mate with #399.
Previous to the 2007 event, the last known cub adoption documented in Yellowstone National Park occurred when grizzly bears still congregated at the open-pit dumps during the late 1960s (Craighead et al. 1995). To our knowledge, the event we documented in Grand Teton was a first for that park.DNA genotyping, combined with sophisticated analytical techniques, allowed us to determine with near certainty the relationships among the individuals involved. In both instances, adult daughters adopted close kin, full-siblings in one event, and a half-sibling in the other. Having daughters living in close proximity to their mother is one aspect of the life history characteristics of grizzly bears that facilitated close kin being involved in the events we observed. While male offspring tend to disperse considerable distances away from their maternal ranges, female offspring tend to establish ranges adjacent to or near their mothers. We do not know for certain the circumstance or events that caused these "family shuffles." Conflicts with male bears looking for mating opportunities (Swenson and Haroldson 2008) or other carnivores can cause separations. Anecdotal reports suggested harassment by wolves may have led to cub separation in the Yellowstone event. We have no information regarding the cause of the Grand Teton event, but another possible scenario might be the inadvertent intermingling of cubs when two females interact.In any case, having adult daughters living in close proximity to their mothers was fortuitous for the young cubs.
In scientific parlance, group-living carnivores (such as wolves) are commonly referred to as "social" species capable of recognizing and choosing to cooperate with others of their kind based on kinship. In contrast, some scientists implicitly or explicitly argue that solitary species such as grizzly bears have little or no opportunity to discriminate kinship once independent from the family group, and individuals consequently compete with their neighbors. The family ties involved in the adoption events we observed dispute this point of view and suggest a much greater knowledge of kinship relations than previously thought. Although we are just beginning to develop an understanding of how grizzly bears communicate, we now have some evidence they likely have an intimate knowledge of their landscape and the other bears with whom they share it.
Craighead, J.L., J.S. Sumner, and J.H. Mitchell. 1995. The grizzly bears of Yellowstone, their ecology in the Yellowstone Ecosystem, 1959-1992. Island Press, Washington D.C., USA.
Haroldson, M.A., K.A. Gunther, and T. Wyman. 2008. Nature note:Possible grizzly cub adoption in Yellowstone National Park. Yellowstone Science 16:42–44.
Harris, R.B., G.C. White, C.C. Schwartz, and M.A. Haroldson. 2007. Population growth of Yellowstone grizzlies: uncertainty, correlation, and future monitoring.Ursus 18:167–177.
Kamath, P.L., M.A. Haroldson, G. Luikart, D. Paetkau, C. Whitman, and F.T. van Manen. 2015. Multiple estimates of effective population size for monitoring a long-lived vertebrate: an application to Yellowstone grizzly bears. Mol Ecol, 24: 5507–5521.
Swenson, J.E., and M.A. Haroldson. 2008. Recent observations of mixed-age litters in brown bear. Ursus 19:73–79.
Last updated: December 21, 2015