Influence of Weather Conditions on Sleeping Patterns and Selection of Foliage Cover of Sleeping Trees in Black-and-Gold, Howler Monkeys ( Alouatta caraya ) in Northern Argentina

Sleeping behaviors, such as sleeping in clusters and sleeping-tree selection, are affected by several social and ecological factors simultaneously, among which weather conditions are suggested to be the most important. We evaluated the relationship between weather conditions (temperature and rainfall) and sleeping-cluster patterns, body posture, and foliage cover at sleeping sites in four groups of black-and-gold, howler monkeys ( Alouatta caraya ) inhabiting San Cayetano (27° 30 'S-58° 41'W), Corrientes, Argentina. During 12 months (between June 2012 and July 2013), we collected clustering, postural, and weather data on 185 days. The number of individuals in sleeping clusters was higher at low temperatures and lower at higher temperatures. At low temperatures, the curled posture was the most frequent, whereas the spread posture increased in frequency as temperatures increased. We did not find a significant relationship between rainfall and sleeping body postures. At low and medium temperatures, individuals selected sleeping trees with dense foliage cover and used open-crowned sleeping trees on rainy days. Consistent with what was found in previous studies, our findings suggest that howler monkeys used behavioral thermoregulation strategies that reduce the exposition to adverse climatic conditions.