Effect of light and temperature on daily activities of the alpine marmot (Marmota marmota Linneus, 1758) in its natural environment

External daily activity was studied in the alpine marmot (Marmota marmota L inne, 1758) in its natural environment in relation to the position of the s un, ambient temperature, and food accessibility. At low temperatures, daily activity starts only when the sun reaches 30% or more above the horizon. D uring temperate periods, external daily activity is closely synchronized wi th 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 co uld be explained by the postponement of feeding when high and uncomfortable midday temperatures limit food accessibility. Our observations under natur al conditions seem to indicate that several factors are involved in the syn chronization of nyctemeral activity in the alpine marmot. The cycle of ligh t, expressed as the height of the sun above the horizon, is the most import ant. However, marmots show different responses to light in the morning and at night. These results corroborate the circadian rhythm model with two osc illators.