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Social organization of the coyote in relation to prey size

University of British Columbia

The typical social unit in coyotes, Canis latrans, is the adult heterosexual pair; young usually disperse during their first year. In some populations, however, some young delay dispersal until after the birth of a subsequent litter. In addition to this variation in sociality, numerous studies have indicated marked variability in the proportion of ungulates in the coyote diet. The ecological correlates of variation in coyote social structure were previously unstudied. Thus, I used the coyote as a test of the hypothesis that sociality in large mammalian carnivores is an adaptation allowing the exploitation of large prey. I studied the social structure and foraging ecology of coyotes in Jasper National Park, Alberta, between 1974 and 1977. Forty-three coyotes consisting of 10 adult males, 10 adult females, six juvenile males and 16 juvenile females were captured 51 times. Twenty-six coyotes (≥ age 6 mon) were equipped with radio-location transmitters to provide information on social structure and systems of land tenure. A large majority of the coyotes in the population were marked or could be otherwise identified. To determine coyote diets, I collected 1,967 known-aged feces from throughout the year. In winter, the Jasper population consisted of approximately 59 percent packs, 17 percent residents pairs, 10 percent solitary residents and 15 percent transients. Packs consisted of three to eight adults, yearlings and non-dependent young. Radio-telemetry data and observations showed that pack members frequently travelled, slept, foraged together and cooperated in territorial defense. Agonistic interactions between pack members reflected their social status within a dominance hierarchy. In coyote packs, I found a clear division of labour in the initiation of territorial defense, scent marking and control of group travel. Packs and pairs defended well defined territories of approximately 8 to 20 km² in winter and probably throughout the year, whereas solitary residents occupied.home ranges which they did not defend. Males and females scent marked their territory throughout the year. The density of scent marks at the edge of the territory was approximately twice that in the center. This was accomplished by reducing the distance between scent-mark locations and increasing the percentage of multiple marks. The scent marks of neighbours were not avoided, but vigorously marked. I found circumstantial evidence that coyotes respected territorial boundaries demarcated by scent marks. In winter, coyote diets consisted primarily of ungulates (67 percent), small rodents (23 percent) and other mammals (7 percent). Young cervids and adult ungulates comprised about 50 percent of the diet in summer. Columbian ground squirrels and small rodents were the other principal foods. Judged against an average of 15 other studies, the mean size of prey eaten by coyotes was larger in Jasper than elsewhere. In Jasper, the percentage of mule deer in the winter diet varied directly with coyote pack size and mule deer density. However, pack size accounted for more of the variation in the amount of mule deer in the diet than mule deer density. In contrast, the percentage of elk in the winter diet was independent of pack size. Since elk were scavenged, their occurrence in the winter diet was primarily a function of the number dying within each coyote territory. I suggest that the success of coyotes in killing mule deer was increased by group foraging. Another possible advantage of cooperative foraging was an increased ability to defend an ungulate carcass against conspecific competitors. Packs had greater access to food and fed longer than single coyotes. There is a correlation between group living in coyotes and the proportion of large prey in the diet. Alternative hypotheses that could account for the variation in coyote social structure in different environments are examined. I conclude that increased sociality in coyotes is an adaptation allowing more efficient capture and/or defense of ungulate prey.

Text

2010-03-11

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http://hdl.handle.net/2429/21790

Zoology

University of British Columbia

Graduate