Seasonal changes in weights of marmots [Variations saisonnière du poids des marmottes].

Résumé

Les variations saisonnières de la masse corporelle chez Marmota flaviventris sont étudiées pendant 8 années au Colorado. Les mâles ont, dans chaque classe de poids, un poids plus élevé que les femelles. Il n'y a pas d'une année sur l'autre de différence dans le taux croissance. Les jeunes de l'année ont moins de réserves graisseuses que les individus plus âgées. Chez les jeunes d'un an et les plus vieux, la masse corporelle est minimale en juin (saison de croissance). Le taux de croissance est plus élevé et rapide dans la période qui suit l'hibernation. Seasonal changes in the body weights of yellow-belIied marmot (Marmota flaviventris) populations were studied for 8 years in western Colorado. Marmots may be classified by size into four age groups : juvenile, yearling, 2-year and 3-year-old or older, each group with significantly different mean body weights. For each age group, the mean body weight of males was significantly larger than that of females. Mean body weights in June of yearlings and older were smaller, the later the onset of the growing season. All age groups made significant weight gains each year, there was no significant difference in growth rates among years. When the rates of weight gain of juvenilles are corrected for time of appearance above ground, the regression coefficients are virtually identical. The earlier young marmots are weaned, the more they weigh at hibernation and the more likely they are to survive hihernation. The percentage of young surviving their first winter of hibernation is significantly greater the earlier spring begins. Marmots at 3400 m elevation had growth rates similar to those of marmots at 2900 m elevation. The adaptive strategy of marmots includes rapid growth rates, high tissue growth efficiencies and extension of the growing season by reproducing immediately following hibernation.