Predation on Yellow-Bellied Marmots (Marmota Flaviventris)
Van Vuren, Dirk H., The American Midland Naturalist
ABSTRACT.-I determined cause-specific mortality of yellow-bellied marmots (Marmota flaviventris) to assess the importance of predation as a mortality factor. Contrary to earlier findings based on visual observation, almost all (98%) mortality during the summer active season was caused by predation. Coyotes (Canis latrans) were the most important predators, followed by badgers (Taxidea taxus), American martens (Martes americana), black bears (Ursus americanus) and raptors, probably golden eagles (Aguila chrysaetos). Predation on marmots is cryptic; none of the predation events were observed and, in most cases, the marmot was consumed or removed so quickly and completely that searching for carcass remains would have been fruitless.
Predation has important behavioral, ecological and evolutionary effects on prey species. The risk of predation may influence foraging behavior (Kotler et al., 1991), social behavior (Fitzgibbon, 1990) and habitat selection (Berger, 1991). Further, removal of individuals by predators may have consequences for population dynamics (Reid et al., 1995) and biogeography (Sievert and Keith, 1985), as well as the evolution of antipredator defenses (Lima and Dill, 1990).
Predation on some large vertebrates can be evaluated through observation (e.g., Fitzgibbon, 1990), but for medium and small species the act of predation is seldom witnessed and the animal may be entirely consumed, leaving no evidence. Disappearance of a marked individual is an unreliable indicator of predation because animals may disappear for other reasons (Murie, 1992; Waser et al., 1994). Moreover, even when predation is established, identification of the predator, an important factor in understanding the effects of predation on the prey, may be difficult (Major, 1991).
The yellow-bellied marmot (Marmota flaviventris) is a large (2-4 kg), ground-dwelling squirrel that is widely distributed in western North America. Anecdotal accounts show that several mammalian and avian predators prey upon yellow-bellied marmots (Frase and Hoffmann, 1980), with potential effects on marmot foraging behavior (Armitage, 1982; Carey and Moore, 1986), habitat selection (Andersen andjohns, 1977), social behavior (Armitage and Johns, 1982) and mating system (Armitage, 1986). However, because predation on marmots is rarely observed (Frase and Hoffmann, 1980), the magnitude of predation and the identity of the predators responsible is rarely, if ever, known. Such is the case for a population of yellow-bellied marmots in the East River Valley in Colorado that has been studied intensively since 1962 (Armitage, 1991). Although coyotes (Canis latrans) and golden eagles (Aguila chrysaetos) were known to prey on these marmots (Armitage and Downhower, 1974; Armitage, 1982), observations of predation were rare (Armitage, 1982), suggesting that it was not a major cause of mortality (Armitage and Downhower, 1974). Radiotelemetry, however, can circumvent biases that affect visual observation as a means of detecting predation. My objective was to use radiotelemetry to assess the importance of predation on yellow-bellied marmots by determining cause-specific mortality during the summer active season.
The study was conducted from 1984 through 1995 in the East River Valley near Rocky Mountain Biological Laboratory (RMBL), Gunnison County, Colorado. Topography was typical of a glaciated, high-altitude valley; slopes were gentle on the valley floor, elevation 2850-2930 m, but rose abruptly to ca. 3900 rn elevation on surrounding peaks. Vegetation was an interspersion of subalpine meadows rich in forbs, aspen (Populus tremuloides) woodlands and spruce (Picea spp.) forests, with dense patches of willows (Salix spp.) along streams. Areas above timberline supported alpine meadows and shrubs, or were largely devoid of vegetation.
Yellow-bellied marmots were common in the valley and lived in discrete habitat patches, typically open meadows relatively free of trees and shrubs that contained rocks (boulders, outcrops or talus) under which burrows were excavated (Svendsen, 1974). …