Coexistence in a Crowded World: Brown Bears and Livestock Depredation
By Kimberly Rigano
People have a history of exploiting carnivore populations. Humans view carnivores as dangerous thieves. In reality, humans and carnivores are just species which happen to share similar needs for high calorie diets and large amounts of land bringing us into competition with one another. This competition often involves food resources and in particular livestock. Bears are particularly large predators with voracious appetites. Conflict between bears and humans is a worldwide problem occurring in “hotspots” where anthropogenic attractants and bear habitat overlap. Conflict is actually increasing in many areas where bears were once eliminated and have now been reintroduced or are expanding their populations. This is in part due to re-growth of forested areas throughout North America providing increased bear habitat. Conflict involving livestock depredation may also be attributed to modern livestock management. People no longer practice traditional methods of livestock management and as a society have effectively forgotten how to coexist with bears.
What is Causing Bears to Attack Livestock?
Bears are omnivores meaning that they will eat a variety of foods from plant matter to insects and meat. They are also hibernators and must consume huge amounts of food during the fall to gain enough weight to survive winter. During this time they can gain over 3 lbs each day (6). Because bears have such high resource demands, it may appear that bears kill livestock out of necessity to fulfill their daily energy requirements. However, in most areas, their diet consists of over 90% vegetation, and depredation does not correlate with the abundance of natural resources indicating that bears do not attack livestock because they are lacking natural sources of food. Data on livestock losses in Europe show that depredation is not the result of large carnivore populations either, as the small population of 25 to 55 bears in Norway kill more livestock than the more than 2,000 bears in Sweden (4).
Instead, attacks on agricultural animals are related to livestock management. Bone yards where ranchers deposit carcasses are the main attractant associated with bear conflict. Certain livestock operations are also more high risk than others. In almost every country where bears and sheep exist together, sheep account for the majority of livestock killed by bears. Sheep are smaller and more vulnerable than cattle with their only defense being their strong flocking instincts. Lambing and calving areas also have high probabilities of bear predation because newly born animals are easy prey. Other livestock management characteristics correlated with high predation rates include animals which are untended for long periods and those that are left out at night when the majority of bear attacks occur.
Another major factor associated with predation is habitat. Most depredation events occur near forest cover with permanent sources of water because this is ideal bear habitat which often overlaps with livestock grazing. In Norway, high levels of depredation are correlated with a large number of sheep grazed near forested areas overnight (4). In the Himalayan Mountains, the majority of sheep are killed during the fall hyperphagic period when bears have an insatiable appetite to gain weight before hibernation. However, the fall was also when sheep were moved into higher elevation alpine meadows where bears in this region reside. Depredation was also associated with lack of human presence (2). In many countries in Europe, people have abandoned their traditional lifestyles of living with and protecting livestock. Today, bear populations are on the rise, especially in Europe and specific areas of the U.S. such as the Northern Continental Divide Ecosystem in Idaho and Montana and Yellowstone National Park, but people remain resistant to changes in livestock management.
Is Depredation a Learned Behavior?
Livestock are an easily accessible food source compared to their wild counterparts. Thus, when bears come in contact with livestock, they often kill more animals than they can eat leaving carcasses behind. Bears are opportunistic feeders, so this is normal adaptive behavior for them as it is advantageous to kill multiple animals at once when predation is easy. This occurs less in the wild because multiple kills are typically difficult with wild ungulates (6). Near Yellowstone, all bears that had access to sheep attacked them. Of the 37 bears collared, only four returned to the same areas at the same time of year after predating livestock (5). All bears that killed livestock exhibited normal foraging behavior similar to that of other bears. This indicates that killing livestock is not a unique behavior that’s only learned by a few problem bears. Livestock depredation is the result of easy foraging opportunities.
There is evidence to suggest that bears do learn some foraging behaviors from their mother. However, in Yellowstone, yearling offspring of problem bears that were then separated from their mother were not more likely to kill livestock than cubs of non-conflict bears, so this is not a behavior acquired during the first year of life. Also, bear depredation is usually concentrated in a few hotspots, and predation rate does not decrease when a few problem bears are removed (6). This indicates that predation is more strongly correlated to habitat attributes. Males are implicated in depredation events more than females. This may be due to the tendency for males to travel more and the greater likelihood for them to come into contact with livestock. There also may be something intrinsic about male behavior that causes them to attack livestock such as boldness or aggression. Yet, few studies have been done on personality differences between conflict and non-conflict bears. Larger male body size and dietary requirements also may cause them to search for food with more protein than females. All bears that attacked full-grown cattle outside of Yellowstone were adult males (5). Bears of all age classes killed sheep, but juveniles exhibited less caution in doing so and were caught and killed more often as a result. One yearling and juvenile male in Wyoming together killed over 30 sheep in one night (6). Adult bears typically kill one or two sheep on the outer edges of the herd and are thus better at avoiding herders. Bears may learn to improve their ability to kill livestock without getting caught. This may mean that juveniles do not necessarily predate livestock at a higher rate; they may just get caught more.
One of the most significant implications of livestock depredation is that it decreases public support for bear conservation which can impact on the probability of survival for bear populations. In fact, plans to reintroduce bears to the Bitterroot Mountains in Idaho were abandoned due to public opposition. For ranchers and livestock owners, hostility toward carnivores, and in particular bears, originates from financial losses incurred by bear predation. Bears do not actually account for a large percentage of overall livestock losses, typically less than 1%, but locally losses can be significant. In Montana, 75% of documented conflict events occurred in “hotspots” that comprised only 8% of the study area (10). On the Upper Green River Cattle Allotment in western Wyoming, uncompensated financial impacts from 1995–2004 due to grizzly bear attacks on calves were $222,500 (9). In the Targhee National Forest twice as many sheep were lost as a result of herding practices as those killed in bear attacks, and yet most livestock managers believe carnivores pose the greatest threat to their animals (5).
Depredation also results in the death of bears when individuals are killed by ranchers as well as legally by the Fish and Wildlife service. Thus, conflict over livestock is a significant source of mortality for brown bears especially in the small, isolated populations such as those that exist in the lower 48 states. Approximately 7% of all human‐caused grizzly bear mortalities between 1998 and 2011 in the Northern Continental Divide Ecosystem were due to management removal actions associated with livestock depredations. At least 51 of 89 management removals were due to attractants such as carcasses that could have been avoided (7). These high removal rates do not always prevent livestock depredation and often result in individual bears being killed that were not involved in the conflict.
Ways to Prevent Livestock Depredation
Change Bear Behavior
Because bears are threatened in the continental U.S., it is important to find nonlethal methods to prevent livestock depredation. Translocating bears involved in livestock attacks to another area may be effective, but may not be desirable as it is stressful for the bear and results in the removal of a reproductively fit individual from the population. Data also indicates that this may not be feasible in areas such as those around Yellowstone where most individuals attack sheep when given the opportunity. Electric fences are expensive and break if not properly maintained. Also, they’re not compatible with sheep grazing because herders have to move their animals throughout the year. Electric fences also produce undesirable effects such as injury and isolation of other wildlife.
Guard dogs can be effective when trained correctly. Properly guarded livestock in the Cantabrian Mountains in Spain and Abruzzo, Italy suffered lower losses than unguarded animals (6). Annual savings due to the use of a livestock protection dog for ranchers from 16 states and 2 Canadian provinces were anywhere from $180 to $14,447 (3). Unfortunately, most of these programs provide livestock owners with puppies, and herders may not have the expertise or the time required for effective training. This can result in aggressive dogs which are a danger to the livestock they were supposed to protect. Aversion techniques using light or noise have been tried but are nearly impossible with bears because they have to be applied right after the behavior and must be highly variable as bears habituate to these stimuli.
Change Livestock Management
A more effective way to prevent depredation is to change the way humans manage livestock. This includes minimizing bone yards and sheep grazing as this has been shown to be incompatible with large carnivore populations. The majority of bear predation occurs at night, so bringing livestock into enclosures or barns at night may reduce attacks. However, these enclosures need to be bear-proof as bears can cause considerable damage if they are able to get into pens causing the sheep to panic and die as a result of crowding and suffocation (4). There is also increased risk when humans are minimally involved with the herds. In the Himalayan Mountains, predation increases when sheep and cattle are left to graze near bear habitat untended for 3 to 5 months (2). Therefore, increased human presence could help reduce conflict. An alternative to protecting livestock within bear habitat is to move high risk operations such as sheep grazing and lambing and calving areas away from key bear habitat. This would involve moving livestock from forested areas as well as rivers and streams. The combination of using off-site water sources along with limiting attractants successfully reduced livestock depredation by bears in Montana (7). However, this requires livestock managers to provide artificial sources of shade for their animals and transport water from off-site locations and may not be realistic for managers with smaller plots of land or in protected areas where grazing is regulated. In areas within one-third of a mile from the electrical grid, an electrical pump is a feasible, cost effective option for transporting water. For 100 cattle, initial costs plus annual electricity was estimated at just under $1000. For areas farther from the electricity, more costly methods are required. A solar powered system to provide water for 100 cattle will cost up to $10000 plus labor to install (8).
Another way to prevent predation without demanding more of livestock managers is to make the livestock themselves more self-sufficient. Flerds may be an effective methods. Flerds are a grazing group of mixed species. Typically, pairing cattle with sheep or another vulnerable animal has been used to prevent predation. The concept of mixed stocking has been around since humans started managing grazers, and research on it began over a hundred years ago.Yet, its use in predation prevention with large carnivores was first proposed in the mid-1980s. The process of creating a flerd involves penning lambs with young cattle to create a bond. In initial trials in New Mexico, no sheep were killed as a result of predation after 30 days of penning with cattle while the rate of predation on non-bonded sheep was 1 every 5 days. A longer initial housing period will result in a stronger bond; however, sheep have become bonded to cattle in as little as 14 days (1). The sheep remain with the cattle at all times and will follow the movements of any cattle, not just those that they were originally housed with. Thus, after the initial housing period where feed is the main cost, this is a relatively easy management strategy. One or more bonded ewes can be used to facilitate the bonding of additional sheep. It is ideal to form a core flerd and then add single individuals to it over time. This system works because of the strong influence of peer behavior on sheep, goats, and other small ruminants.
Flerds have also been shown to improve foraging efficiency of individuals and increase vegetation heterogeneity since species have variable diets and utilize different parts of the land. Sheep will graze in areas that cattle will not thus utilizing a greater proportion of the pasture. Flerds also spread themselves more uniformly over the pasture than single species grazing groups. Initial start-up costs and time requirements involved in creating a flerd may be high, but long-term management declines. Less fencing can be used as cattle require fewer wires to contain them. This benefits wildlife by creating fewer barriers and livestock managers by bringing down costs. Over a quarter mile of fencing, adding two extra wires can cost an additional $66. When miles of fencing are required, savings can be significant (1).
Bear attacks on livestock account for a small percentage of total livestock losses. However, depredation events are increasing in areas where bear populations are expanding their range, and livestock depredation greatly reduces public support for bear conservation. It also results in high mortality in some areas where bears involved in depredation are killed by humans and thus represents a serious threat to survival. Data indicates that livestock predation is not a learned behavior, but is instead the result of an innate tendency for bears to exploit easy foraging opportunities. Livestock at high risk of bear attacks include sheep grazed in key bear habitat as well as animals which are left untended for long periods of time and left in open pastures as night. Changing the behavior of a wild carnivore is difficult, so techniques which alter livestock management may be more effective measures of preventing depredation. These include enclosing livestock and moving them away from bear habitat. Flerds may represent a revolutionary idea for preventing depredation.
- Anderson, D. M., E. L. Fredriskson, and R. E. Estell. 2012. Managing livestock using animal behavior: mixed-species stocking and flerds. Animal 6:1339-1349.
- Chauhanl, N. P. S. 2003. Human casualties and livestock depredation by black and brown bears in the Indian Himalaya, 1989-98. Ursus 14:84-88.
- Gehring, T. M., K. C. VerCauteren, and J. Landry. 2010. Livestock protection dogs in the 21st century: Is an ancient tool relevant to modern conservation challenges? Bioscience 60:299-308.
- Kaczensky, P. 1999. Large carnivore depredation on livestock in Europe. Ursus 11:59-72.
- Knight, R. R. and S. L. Judd. 1983. Grizzly bears that kill livestock. International Conference on Bear Research and Management 5:186-190.
- Linnell, J. D. C. et al. 1999. Large carnivores that kill livestock: do “problem individuals” really exist? Wildlife Society Bulletin 27:698-705.
- Mace, R. 2013. NCDE grizzly bear conservation strategy. Montana Fish, Wildlife and Parks. Helena, MT, USA.
- Marsh, L. 2009. Pumping water from remote locations for livestock watering. Biological Systems Engineering, Publication 442-755, Virginia Cooperative Extension, Petersburg, VA.
- Sommers, A. P. et al. 2010. Quantifying economic impacts of large-carnivore depredation on bovine calves. Journal of Wildlife Management 74:1425-1434.
- Wilson, S. M. et al. 2005. Natural landscape features, human-related attractants, and conflict hotspots- a spatial analysis of human-grizzly bear conflicts. Ursus 16:117-129.
About the Author
Kimberly Rigano is a MS student in the School of Biological Sciences at Washington State University. She is currently studying grizzly bear physiology examining seasonal changes in insulin sensitivity. Her research focuses on better understanding adaptations for hibernation in relation to bear ecology as well as discovering possible applications to human health.