Socioecology of Marmots: Female Reproductive Strategies

Abstract

The relationship between female reproductive success and both spring food and hibernacula resources was examined in a high-altitude population of yellow-bellied marmots (Marmota flaviventris). The number of offspring a female weaned was significantly associated with the estimated number she could potentially produce, based on food resources. The production of young by these females is probably food limited to varying degrees. Hibernacula may be a restricted resource; young reared in an area without a hibernaculum were not recaptured as yearlings. Delaying pregnancy until forage is available fails as a strategy because young have insufficient time to accumulate fat for hibernation. Adult females deposit fat at a single maximum rate regardless of reproductive history; few females gain weight prior to weaning their young. In areas with short growing seasons, measured as the period during which nonreproductive adults gain weight, females may occasionally or regularly fail to reproduce in consecutive years. The short period of time following weaning may not permit the accumulation of fat sufficient to provide energy for hibernation, postmergence activity, and reproduction. The growth rate (g/day) of young marmots is greater at high than at intermediate elevations. This increase in growth rate warrants further examination of the hypothesis that increased sociality among marmots living in areas with short growing seasons is a response to decreased growth rates of young animals.