Behavioral ecology of alpine yellow-bellied marmots

Summary

• 1. An investigation of the behavior and ecology of several contiguous harems of yellow-bellied marmots (Marmota flaviventris) was conducted in an alpine area of North Pole Basin, Gunnison County, Colorado. At an elevation of 3,400 m, the study site differed from those of previous marmot studies in that no forest restricted interharem movement or social contact.

• 2. Meadow vegetation was patchily distributed and covered half the study area; clumps of willow comprised most of the remaining vegetation. Eighty-two marmot burrows within the study area (most of which were unoccupied) were randomly distributed. The 26 most frequently occupied burrows (hibernacula and summer residences) also had a random spatial distribution.

• 3. Two or more marmots commonly occupied the same hibernacula and summer residence burrows, resulting in a highly clumped spatial distribution of marmots.

• 4. Ecological densities of adult and yearling residents in North Pole Basin were usually higher than densities at East River Valley study sites in the same region (Table 9).

• 5. In contrast to annual reproduction commonly observed at lower elevations, no alpine female marmot was observed to produce young in consecutive years.

• 6. Burrowmates were generally much more closely related than nonburrowmate members of the same harem (Table 4).

• 7. The intensity of foraging activity varied throughout the active season, being low in May, June, and September and very high in July and August (Fig. 1). Forage ranges of individuals varied in size from 0.1 to 2.2 ha (Table 5), and were larger in the year of low food availability. The average degrees of forage range exclusivity for each level of social organization were: individuals, 10%; burrow groups, 41%; and harem groups, 88%.

• 8. Rates of social interactions changed throughout the active season; agonistic and sexual rates of interactions generally decreased and the amicable interaction rate generally rose between early June and late August (Fig. 6).

• 9. Among burrowmates, social interactions were predominantly amicable. But between nonburrowmate members of the same harem and between members of different harems, agonistic interactions predominated.

• 10. Yearling offspring that remained resident in their natal harem throughout the summer had predominantly amicable social interactions with their parents. Social interactions of these yearlings with nonparent adults were primarily agonistic ones in which the yearlings were subordinant.

• 11. Environmental parameters, population dynamics, resource utilization patterns, and social dynamics were evaluated in terms of their relationships to population density, intraspecific competition, parent—offspring relations, and male territoriality.