Anthropology, Yale University
April 12, 2018 3:00, Texas V/VI
Endotherms benefit by being active during the warmer periods of the 24-h cycle and resting when temperatures drop because this results in lower energetic investment in thermoregulation. In accordance with this hypothesis, the cathemeral Azara’s owl monkeys of the Argentinean Chaco (Aotus azarae) increase daytime activity during the relatively cold austral winter. Still unclear is how changes in ambient temperature may influence, during daytime, the allocation of time to behaviors that tend to conserve energy (resting), to increase its availability (foraging), or to use it (traveling). We constructed an a priori set of linear models to evaluate the separate relationships between photoperiod, moonlight, age class, reproductive status, and hourly and daily measures of ambient temperatures. We predicted that at colder temperatures monkeys would spend more of the daytime foraging and less traveling and resting to compensate for an increase in thermoregulatory needs. We analyzed 5516 20-min focal observations collected between 06:00-21:00 hs from 146 recognizable monkeys during 2001-2015. Our results indicate that, from the warmest to the coldest months, individuals decreased the average frequency of daytime resting by 30%, and, when active, monkeys decreased the average frequencies of daytime traveling behaviors by 40% and increased the average frequency of daytime foraging by 80%. Daytime resting, traveling, and foraging frequencies were best explained by the temperatures at the time when animals were sampled but not by other factors in the models fitted. Our results suggest that the cathemeral behavior of A. azarae may be influenced by patterns of ambient temperature.
This work was funded by the National Science Foundation (NSF-BCS-0621020, 1503753, 1219368, 1232349, 1540255, and 1503753).