Food Habits of Wolves in Relation to Livestock Depredations in Northwestern Minnesota
Chavez, Andreas S., Gese, Eric M., The American Midland Naturalist
Wolves (Canis lupus) have recolonized many areas of the Midwestern United States, prompting concern over the possible risk wolves may pose to livestock producers. To better understand the risks wolves may pose to livestock, we initiated a 3-y study examining the food habits of wolves in an agricultural area of northwestern Minnesota and their relation to depredation records of livestock losses in the same area. We collected 533 wolf feces during the non-winter seasons from 1997-1999. White-tailed deer (Odocoileus virginianus) was the most abundant food item (39.2%) of all prey items for all 3 y combined. The deer component comprised both adult deer (26.9%) and fawns (12.3%). Muskrats (Ondatra zibethicus) were the second highest food item at 16.6%. Moose (Alces alces), both adults (13.0%) and calves (0.6%), comprised 13.6% of the diet of wolves, followed by cattle (10.3%), domestic pig (4.4%), lagomorphs (3.6%) and beaver (Castor canadensis; 2.1%). During our 3-y study, eight head of livestock were officially reported as wolf depredations in the agricultural lands within the study area. The confirmed losses included one sheep, one injured cow, one blind cow and five calves. Even with very low deer and moose densities in the study area and a high preponderance of cattle in the area (>1000 head), the wolves in the area preyed mostly on native prey species.
The historical range of the gray wolf ( Canis lupus) included most of North America where wild ungulates were abundant (Carbyn, 1987). European settlement along with the introduction of domestic livestock into these areas altered the relationship between wolves and their native prey. Across the contiguous United States, domestic livestock replaced or coexisted with native ungulates. Wherever wolves and livestock coexisted, wolf depredations on livestock occurred (Young and Goldman, 1944; Gunson, 1983; Tompa, 1983; Fritts et al, 1992). As a result, the threat of wolf predation on domestic livestock became one of the leading reasons for humans to eradicate wolves throughout the contiguous United States. By the middle of the 20th century, humans had successfully eradicated wolves from most of the contiguous United States, except for a single population in northeastern Minnesota.
The distribution of wolves in the contiguous United States began to increase during the latter half of the 20th century due to increasing public empathy (Mech, 1995). This shift in public attitude prompted the U.S. Fish and Wildlife Service to protect the wolf in 1974 under the Endangered Species Act. In 1978 the Eastern Timber Wolf Recovery Team set forth guidelines for the recovery of wolves into parts of their former range in the upper Midwest. Wolves were able to rapidly recolonize most of the northern forests in the upper Midwest because these areas supported high deer populations that wolves used as their primary prey (Fritts and Mech, 1981; Fuller, 1989). As most of the northern forest in Minnesota became saturated with wolf packs, wolves began establishing territories in peripheral semi-agricultural areas containing abundant livestock and native prey (Fuller et al, 1992; Berg and Benson, 1999). This population expansion of wolves into semi-agricultural areas culminated in increasing concerns from farmers about wolves killing livestock (Mech et al, 1988; Mech, 1995).
Little is known about the feeding ecology of wolves in a semi-agricultural area in the upper Midwestern U.S. Studying the food habits of wolves in a semi-agricultural system is necessary because it permits a more objective understanding of wolf behavior and ecology in relation to their prey (e.g., Mills, 1996). We examined the food habits of wolves in a semiagricultural area of northwestern Minnesota during the non-winter seasons. Our objective was to document the food habits of wolves during the time of year that livestock were grazing in pastures (non-winter seasons), document the number of livestock killed by wolves and investigate factors influencing wolf diet in an area with both native and domestic ungulates. …