Dispersal of yellow-bellied marmots [La dispersion des marmottes à ventre jaune].

Résumé

I used radio-telemetry to describe dispersal of yellow-bellied marmots (Marmota flaviventris) and to assess the fates of dispersing marmots. Transmitters were surgically implanted into the peritoneal cavity, neither surgery nor the transmitter had any discernable effect on survival, growth or reproduction. Marmots dispersed primarily as yearlings, altough some delayed dispersal until as old as three years. Most dispersal occured May trough July. Dispersal direction was nonrandom. Dispersal distance distributions were skewed for both sexes, altough marmots dispersed as far as 15.5 km, most settled within 500 m. Three patterns of dispersal were identified. Some dispersers emigrated abruptily, whereas others dispersed through a gradual process. Some marmots, mostly males, dispersed in two stages. Dispersing females suffered higher mortality during transience, solely because of predation, than did females that remained philopatric. Therafter, survival of dispersing and philopatric females was similar. Age at first reproduction among females was similar for dispersers and for philopatric residents, but frequency of reproduction apparently was lower for dispersers. Survival of male and female dispersers was similar except during summer the year after dispersal. Marmots that delayed dispersal until older than one year gained no survival advantage. Marmots that dispersed more than 500 m suffered higher mortality than did marmots that dispersed shorter distances. Five predators of marmots were identified, primarily by tooth impessions left in the wax coating of recovered transmitters, coyotes (Canis latrans) were the principal predator. Analysis of coyote scats suggested that marmots were alternate prey sought when preferred prey were scarce. Data from scats and recoverd transmitters indicated that marmots were most vulnerable to predation in July and that vulnarability of yearling and adults were similar. Survival rates of males and females were similar until reproductive maturity at two years of age during the third summer of life, males suffered higher mortality than females. The female-biased sex ratio was caused solely by predation on males, primarily during the third summer.