The influence of abiotic factors on the onset and cessation of activity of semi-free Callithrix jacchus.

Abstract

The influence of abiotic environmental factors on the period of activity of a single group of South American common marmosets (Callithrix jacchus, Callitrichidae, Primates) was investigated under semi-free conditions. A group of eight members had a territory consisting of a heated wooden hut with a veranda, surrounded by an open area with a few trees (ca. 3.5 m high) and three runways made out of roofing slats, on which feeding places and sleeping boxes were fixed. The food supply was held constant throughout the observation period with respect to amount, composition and spatial distribution. From July to November 1995, the times of the onset and cessation of activity were determined using a video camera. An electronic weather station recorded the temperature, humidity, air pressure, wind speed, wind direction, precipitation, and light intensity at intervals of 5 min. There was a linear correlation between day light length and the length of the period of activity over a day length of 10 to 14 hr. With shorter day lengths, the marmosets were also active during the twilight, whereas with longer day lengths a sleep phase during the late morning was introduced. Ambient temperature and humidity had also an effect on the time when activity began or ceased. Callithrix jacchus has one of the longest activity periods within the Callitrichidae. The time of sunrise or sunset, temperature, and humidity accounted for 66.2% of the variation in the time when activity began and 75.5% of the variance in the cessation of activity of the study group within the multivariate model. The results from the present study add to the indications that in the Callitrichidae there is a strong selection pressure for the highest possible energy saving during the comparatively long phase of inactivity.