NATIONAL PARK SERVICE Research in the Parks NPS Symposium Series No. 1

INTRODUCTION

Records on grizzly bear (Ursus arctos) injuries to humans in Yellowstone National Park between 1930 and 1969 and data which suggested causal relationships were compiled for reference purposes (Cole 1970a). These compilations indicate that unnatural food (human camp groceries or garbage) altered the natural habits and behavior of bears and was basically responsible for 60 injuries which occurred within park developments (campgrounds, cabin complexes, etc.). During this 40-year period, three other injuries to hikers in backcountry areas appeared to be due mainly to the natural defensive behavior of female grizzlies with young.

Changes in bear-control procedures seemed to be partly responsible for a fivefold increase in injury rates from the 1950s to the 1960s. Individual bears that became habitual users of developed areas and would have been destroyed during the 1950s were repeatedly captured and transplanted in the 1960s. This allowed grizzlies that learned to avoid capture or returned from transplants to mate and raise young within areas that received high levels of human use. The number of injuries in park-developed areas markedly increased in 1963 and averaged 4.5 per year between 1963 and 1969.

Repeated visits of bears to developed areas or garbage disposal sites to obtain food represent reward-reinforced behavior (Stokes 1970). The usual avoidance behavior of grizzlies toward humans was apparently lessened by repeated "rewards" of food in association with campers or with persons that worked at or hauled garbage to disposal sites. Unnatural movements and distribution habits apparently resulted from bears having prior experience in feeding at garbage disposal sites (Jonkel 1967; Hornocker 1962; Murie 1961) or in campgrounds.

After reviews of available reference information and various recommendations, the Superintendent of Yellowstone National Park directed that a program be implemented to (1) restore bears to using natural food entirely, and (2) reduce injuries to humans. Research personnel were asked to assist on program design and to carry out studies to document and evaluate results.

Most of the data that were considered in developing the park's program are summarized in reports by Craighead and Craighead (1967), Martinka (1971), and Cole (1970a). The final program outlined a sequence of management actions to eliminate sources of unnatural food that attracted bears into park-developed areas, procedures for controlling bears and protecting visitors, and an open-ended schedule for closing the last two large garbage dumps that remained in the park. A more detailed description of the program, its backup contingencies, and its first year results in 1970 have been presented as a conference paper (Cole 1970b).

This paper will Summarize the various management actions carried out in both 1970 and 1971, describe the procedures used for evaluation studies, and attempt a preliminary evaluation of program results. Evaluations will be in relation to the general objectives of reestablishing a natural grizzly population and reducing injuries, with an assessment of effects on bear numbers.

MANAGEMENT ACTIONS

Figure 1 shows the location of major park developments and garbage disposal sites that are referred to in this report. Bearproof tops had been placed on the garbage cans within all park campgrounds and picnic areas prior to 1970, within all but two cabin or residence complexes by 1971. Over 2000 such cans now are placed within the park.

Fig. 1. Map of Yellowstone National Park showing the location of major park developments and garbage disposal sites.

Efforts were intensified to have visitors store food so it would not lure bears into campgrounds. This involved distributing literature at park entrances, posting warning signs, and advising campers by ear radio messages, public address systems, and direct contacts. Literature on "how to camp and travel in bear country" was also distributed to backcountry campers and hikers.

The Rabbit Creek and Trout Creek garbage dumps inside Yellowstone National Park were closed (i.e., not used since the previous year) consecutively in 1970 and 1971. A large municipal dump that was just outside the park's west boundary and within 2 miles of West Yellowstone, Montana, was also closed by the U.S. Forest Service in the early summer of 1971. Most of the bears that used this boundary-area dump were assumed to be members of the park population (discussed later).

Based upon studies by Hornocker (1962), up to 40 different grizzlies may have visited the Rabbit Creek dump over June-September periods. Up to 100 different bears may have visited the Trout Creek dump. Up to 40 different bears may have visited the West Yellowstone dump. Refuse that had previously gone to these sites went to three fenced, sanitary landfills and two incinerators.

Park campgrounds in superior spring and fall grizzly habitat were opened later and/or closed earlier than previous years to avoid peak periods of grizzly activity. Other campgrounds provided substitute camping. Tent or sleeping-bag-only camping was prohibited in one campground to gain experience in applying such management actions if they became necessary.

One control action was recorded each time a bear was either captured and transplanted, shipped to a zoo, or destroyed. Efforts to promptly remove bears from park developments were intensified in 1970 and 1971. Bears were captured with baited culvert traps or with drugs (Sucostrin or M99) administered by a projectile syringe. A small, serially numbered tag was placed in the ear of animals that were to be transplanted and did not already have identifying markers. Transplants which placed bears an average of about 30 miles (6-51) from capture sites were made routinely by vehicle, boat, or helicopter.

Bears were intentionally destroyed and processed as scientific specimens if they could not be removed from a developed area by live capture methods, if they became excessively destructive or dangerous to humans, or if they had returned from one or more transplants. Young bears, as well as older animals that may have simply been passing through a developed area, were given repeated transplants. Unintentional deaths occurred when bears injured themselves in traps, charged personnel that were attempting immobilization, or failed to recover from drugs.

A central monitoring system that recorded grizzly observations, human injuries, property damage, and bear control actions on a daily basis provided current information for guiding the overall program and data for evaluation studies.

STUDY PROCEDURES

The hypotheses being tested to evaluate the park's program are:

(1) The various management actions to remove unnatural food sources and bear control procedures applied in the 1970s will: (a) progressively reduce the incidence and numbers of grizzly-caused injuries in park-developed areas from the 1963-69 average of 4.5 (2-8) per year; and (b) restore a more natural grizzly population than existed in the 1960s, as evidenced by bears occurring in scattered distributions in summer, an increase in avoidance behavior toward humans, and progressive reductions in the numbers of bears controlled and destroyed.

(2) The bear control procedures applied in the 1970s will not prevent the park grizzly population from maintaining or rapidly reestablishing its numbers at natural carrying-capacity levels.

A general model of the different units in the park's grizzly population was constructed in 1970 to predict probable removals of bears and assess what would constitute excessive control mortality. Data from Hornocker's (1962) censuses of bears at dumps, as well as park records on bears within different developed areas, were used to estimate the numbers of grizzlies that used unnatural food. Field observations of grizzlies and their sign in different areas by park personnel as well as the findings of Barnes and Bray (1967) on grizzly and black bear (Ursus americanus) numbers in remote areas, were employed to estimate the numbers of grizzlies that would not be directly affected by eliminating unnatural food. The various population units with estimated numbers were as follows:

The effects of removing bears on population numbers were assessed from considerations of the logistic growth equation

dN/dt = rN([K-N]/K)

Stated in words, this is simply that the rate of change in population numbers with time (dN/dt) is due to the difference between birth, death, and emigration rates which are influenced by the size of the population (N) in relation to the carrying capacity of its environment (K). The relationship where dN/dt averages zero when N equals K was assumed to apply to Yellowstone grizzlies. Immigrations are ignored because of the relatively low grizzly densities outside the park.

The carrying capacity of the park environment for grizzlies was probably determined by social interactions among the bears themselves, and by intraspecific and interspecific competition for natural fall or spring foods that were periodically in limited supply. These relationships were inferred from studies by Jonkel (1967), Murie (1961), Martinka (1970), and Cole (1972).

Additionally, a "core" population of grizzlies that remained within the park and was not subject to hunting or conflicts with agriculture was distinguished from an unknown number of bears that had all or portions of their home ranges outside park boundaries. Emigrations of young adult or displaced old bears, or kills of such animals outside the park, were considered to show that the core population was at carrying capacity (Cole 1970a). Bears that made summer migrations into the park to use garbage dumps (Craighead and Craighead 1971) were not considered members of the core population. According to Jonkel (1967), such migrations probably result from a subadult bear acquiring experience in using a dump, before it has to emigrate to find a vacant home range.

The 200 bears that were estimated to be variously affected by removals of unnatural food were also assumed to be at carrying capacity with dN/dt averaging zero. Craighead and Craighead (1971) reported increases of about six bears per year in this population segment, but they did not consider that emigrants were no longer members of the park population.

PROGRAM RESULTS

Injuries

Table 1 shows the number of injuries in park-developed areas that were attributed to grizzlies during 1970, 1971, and four previous decades. The details relating to previous years have been published elsewhere (Cole 1970a). The two persons injured in 1970 were at the same campsite. A female bear which may have reacted to "defend" her cub injured both persons. No injuries were recorded for 7 years during the 1930s, 6 years during the 1940s, and 5 years during the 1950s. Injuries occurred every year in the 1960s. The zero injury record for 1971 was the first in 15 years,

TABLE 1. Numbers of injuries to humans from grizzly bears by periods and years, Yellowstone National Park, 1930-71.

Bear Control Actions

The numbers of control actions (CA's) that occurred in different park developments from 1968 to 1971 are shown in Table 2. Data prior to 1968 were incomplete because all captures and transplants of unmarked bears were not recorded. Unmarked bears also precluded knowing the number of individual animals handled in 1968 and 1969.

TABLE 2. Numbers of grizzly bear control actions in Yellowstone National Park developed areas, 1968-71.

Numbers of Control Actions and Bears

In comparison with 1968 and/or 1969, the increase in CA's during 1970 occurred mainly in the Old Faithful development and some smaller units (Table 2). Six of the 13 CA's in small units and 2 in other large developments involved bears that had been transplanted from the Old Faithful area. In total, 30 of the 70 CA's in 1970 could be at tributed to 18 Old Faithful bears. The remaining 40 CA's in other developments involved 32 different bears. Of the 12 bears destroyed, 6 were intentional and 6 were unintentional. Eight other animals (seven had returned from one or more transplants) were shipped to zoos.

Table 2 shows the numbers of CA's within the park decreased in 1971. The 39 CA's involved 33 different bears. Of the six bears destroyed, four were intentional and two unintentional. In contrast, the number of CA's in Montana's West Yellowstone area during 1971 increased from previous years. Here Montana Fish and Game personnel carried out 23 CA's which involved 19 different bears. Twelve of these bears were known to be killed: one bear that was considered excessively dangerous and four that returned from transplants into the remote Absaroka Range north of Yellowstone National Park were intentionally destroyed; one failed to recover from drugs; three were illegally shot; and three others were legally killed by hunters. Additional bear mortality due to humans occurred within the park with two grizzlies struck by cars in 1970; one, in 1971.

Transplant Success

Twenty-two marked or identifiable grizzlies were transplanted a total of 54 times and returned to the same or another park-developed area 36 times in 1968 and 1969. This amounts to only 33% of these transplants being successful in preventing returns to developed areas. About 60% of 50 transplants were successful during 1970. About 80% of 33 transplants were successful during 1971, and only three bears that were transplanted the previous year were rehandled.

DISCUSSION AND CONCLUSIONS

The basic premises of the park's program were (1) the "right" number of grizzlies within Yellowstone National Park is the number that occurs naturally (i.e., without human influences on bear behavior, habits, or population dynamics); (2) removals of unnatural food and in corrigible bears will allow young bears without human-altered behavior or habits to progressively replace incorrigible animals in the population; and once this is accomplished (3) the control of human influences alone will prevent corruptions of new bears and thereby substitute for controlling bears.

Some inadequacies were evident in the program. Despite the intense efforts to inform campers on how to store food in bear country, some ice chests or boxes that contained groceries were left out each night. Sufficient amounts of such food were available in larger campgrounds to encourage repeated visits by at least one and sometimes several grizzlies. Unless this food-storage problem is solved, the need to control bears in some campgrounds could continue indefinitely. Some possible solutions are to strictly enforce an existing regulation which requires proper food storage, condition bears to avoid camp groceries, enclose problem campgrounds within a bearproof fence, or provide substitute campgrounds outside the park.

Some unnecessary control actions and potential for injuries occurred from a reluctance to dispatch the few adult female bears that continued to frequent park campgrounds in the 1970s. These females attracted males that became highly aggressive during the June and July breeding period. The survival of such females could also allow family groups of bears again to become habitual users of campgrounds. Unnecessary control actions also occurred because individuals in cabin areas, trailer courts, and residences did not place refuse in bearproof cans. A possible solution to such negligence is to assess the cost of capturing and transplanting bears to persons who make control action(s) necessary.

Appropriate tests for differences in the incidence and numbers of grizzly-caused injuries in park developments between the 1960s and 1970s will require data from several more years. Based on the preliminary 1970 and 1971 data, the hypothesis that the park program will progressively reduce injuries does not need to be rejected. The alternative hypothesis that the program will increase injuries, or the null form that it had no effect on injuries, is not supported by the preliminary data. Progressive removals of certain bears that had been repeatedly handled and transplanted in the past are suspected to have contributed to the absence of injuries in 1971.

Adequate tests of the hypothesis that the park program will progressively restore a more natural grizzly population will also require a longer time span. Monitoring records for 1970 and 1971 were obtained from a total of 1188 grizzly observations. These suggested that with the closure of the last garbage dump in 1971, the majority of the park's bears stayed in scattered distributions on natural foods through the summer. Records of grizzly occurrences in developed areas, as well as the reduced numbers of CA's and bears destroyed in 1971, also show that considerably fewer grizzlies used park-developed areas than in previous years.

The increased success in transplanting bears (33% in 1968 and 1969, 60% in 1970, 80% in 1971) probably was due partly to selective removals of bears that had prior experience in returning from transplants. It is also suspected that with reduced food rewards in developed areas, the capture and transplant process became sufficient "punishment" to discourage bears from returning to these areas. The distances that bears could be transplanted in the park (up to about 50 miles) did not seem significant to overcome the homing capabilities of most adults. Transplanted adults that returned to Montana's West Yellowstone area traveled over 70 miles.

Reference literature from the applied field of wildlife management shows that mortality from humans can substitute for density-influenced mortality from natural causes when animal populations are at or near the carrying capacity of their environment. It should be added that human-induced mortality could also reduce the number of emigrants when population densities are influenced by social or competitive interactions.

If the park grizzly population was at or near carrying capacity in 1970, the removal of 20 bears by control operations and the deaths of two animals hit by cars could be expected to substitute for some mortality or emigrations that would have otherwise occurred. Another increment of even less than 30 cubs in 1971 could be expected to reestablish population numbers at or near original 1970 levels. The removal of 6 bears by park control operations and one car-caused death in 1971, as well as the additional deaths of 12 bears that resulted directly or indirectly from the Montana Fish and Game Department's program, also do not seem of sufficient magnitude to prevent the park grizzly population from regaining its numbers by 1972 or 1973. Here, it is anticipated that the numbers of CA's within the park will continue to decline and bear control in Montana's West Yellowstone area will follow the pattern shown by the 1970 and 1971 data for the park's Old Faithful area (Table 2). The foregoing considerations of bear population dynamics in relation to human-induced mortality suggest that the control procedures applied in the 1970s will not prevent the park grizzly population from maintaining or rapidly reestablishing its numbers at carrying capacity.

Appropriate summary conclusions are as follows: the preliminary results of the program show initial trends toward accomplishing the objectives of restoring a natural grizzly population and reducing injuries to humans. Thus far, the removals of bears from the core park population could temporarily reduce density-influenced emigrations. Such emigrations will probably be reestablished at higher-than-previous rates because the first-year survival of cubs is considerably greater in free-ranging bear populations than in population segments that concentrate at garbage dumps (Martinka 1970). Removals of bears have not been and probably will not be sufficient to preclude the park population from maintaining or rapidly reestablishing its numbers at capacity levels by density-influenced recruitments of young. The "need" to remove or otherwise control bears will probably decline to relatively low levels in subsequent years.

REFERENCES

BARNES, V. G., and O. E. BRAY. 1967. Population characteristics and activities of black bears in Yellowstone National Park. Final Report. Colorado Coop. Wildl. Res. Unit, Colorado State Univ. 199 p.

COLE, G. F. 1970a. Preservation and management of grizzly bears in Yellowstone National Park. BioScience 21(16):85 8-864.

______. 1970b. Grizzly bear management in Yellowstone Park. 1970. 2nd Int. Conf. on Bear Res. and Mgmt., Univ. of Calgary, Alberta, and Res. Note No. 3, Yellowstone National Park. 14 p.

______. 1972. Grizzly bear-elk relationships in Yellowstone National Park. J. Wildl. Manage. 36(2):556-561.

CRAIGHEAD, J. J., and F. C. CRAIGHEAD, JR. 1967. Management of bears in Yellowstone National Park. Environ. Res. Inst. and Motif. Coop. Wildl. Res. Unit Rep. 113 p.

______. 1971. Grizzly bear-man relationships in Yellowstone National Park. BioScience 21(16):845-857.

HORNOCKER, M. G. 1962. Population characteristics and social and reproductive behavior of the grizzly bear in Yellowstone National Park. M.S. Thesis. Montana State Univ., Missoula. 94 p.

JONKEL C. J. 1967. Black bear population studies. Job Compl. Rep. W-98-R, Montana Fish and Game Dept. 147 p.

MARTINKA C. J. 1970. Grizzly ecology studies. Glacier National Park, 1969. Natl. Park Serv. Prog. Rpt. 43 p.

______. 1971. Status and management of grizzly bears in Glacier National Park, Montana, Trans. N. Am. Wildl. Nat. Resour. Conf. 36:312-322.

MURIE, A. 1961. A naturalist in Alaska. The Devin-Adair Co., New York. 302 p.

STOKES, A. J. 1970. An ethologist's views on managing grizzly bears. BioScience 20(21):l 154-1157.

Acknowledgments

Dr. Allen W. Stokes and Dr. Barrie K. Gilbert, Utah State University; Dr. Douglas B. Houston, Research Biologist, and Mr. Dale H. Nuss, District Ranger, National Park Service, Yellowstone National Park, reviewed the manuscript and made helpful suggestions. This paper is a contribution from the National Park Service Natural Sciences Project YELL-N-38.