Effet de la lumière et de la température sur le rythme d'activité de la marmotte alpine (Marmota marmota Linné, 1758) en milieu naturel

External daily activity was studied in the alpine marmot (Marmota marmota Linné, 1758) in its natural environment in relation to the position of the sun, ambient temperature, and food accessibility. At low temperatures, daily activity starts only when the sun reaches 30° or more above the horizon. During temperate periods, external daily activity is closely synchronized with the height of the sun (16°-17° above the horizon). However, on hot days the duration of surface activity of alpine marmots at the end of the day could be explained by the postponement of feeding when high and uncomfortable midday temperatures limit food accessibility. Our observations under natural conditions seem to indicate that several factors are involved in the synchronization of nyctemeral activity in the alpine marmot. The cycle of light, expressed as the height of the sun above the horizon, is the most important. However, marmots show different responses to light in the morning and at night. These results corroborate the circadian rhythm model with two oscillators.