Thermal influences on the activity and energetics of yellow-bellied marmots (Marmota flaviventris) [Influences thermiques de l'activité et de l'énergétique des marmottes à ventre jaune (M. flaviventris)].

Résumé

The thermal environment of microhabitats used by yellow-bellied marmots (Marmota flaviventris) at three study sites in the Elk Mountains of southwestern Colorado was characterized using the standard operative temperature (Tes) method. Marmots typically used only two abovegraoud microhabitats - meadows, where they foraged, and rocks near the burrow, where they often sat. The Tes's calculated for foraging areas were often below 0° before 0800 hours and often exceeded the upper limit of marmots' thermoneutral zone from late morning to midafternoon on clear days. Higher wind speeds over rocks produced Tes's up to 10° C less than in foraging areas. Marmots responded to stressfully high Tes's by reducing above-ground activity, reducing the length of foraging bouts, and tolerating transient increases in body temperature. Foraging activity during midday hours was greater on cloudy days and at a high elevation site with lower average Tes's. Young responded to stressfully low Tes's by timing daily activity to avoid the lowest Tes's. Altough mmarmots generally avoided foraging at the most stressfull Tes's, they sometimes foragedat stressful Tes's, presumably when that option was necessary to meet daily energy demands and preferable to the lternative of forgoing foraging. Under most conditions, stressful Tes's did not appear to limit time needed for foraging, but thermal constraints may have been important for young that also faced declining food quality at the end of the growing season.