Archived Abstracts
Seasonal variation in the length of the daily activity period in buffy-headed marmosets (Callithrix flaviceps): an important consideration for the analysis of foraging strategies in observational field studies of primates
Authors: Stephen F. Ferrari, Renato R. Hilario
Activity budgets – the average proportion of time devoted to different behaviors – are widely-used in primate field studies for the understanding of behavior patterns. In some cases, there is considerable seasonal variation in the length of the period the animals are active each day, which may affect the reliability of these budgets. In this study, activity budgets from two field studies of buffy-headed marmosets (Callithrix flaviceps) were first compiled by the traditional approach (proportion of records) and then by considering the time dedicated to each category over the 24-hour cycle (adjusted budget). Both groups were typically active for 1-2 hours less than the daylight period, with significantly shorter activity periods during the austral winter, when the daylight period was up to 2:35 h shorter than in the summer. The traditional time budgets indicated that the members of both groups spent significantly more time foraging during the resource-poor winter months. However, the time-adjusted budgets led to the conclusion that, rather than spending less time foraging when resources were more abundant during the summer months, the marmosets actually spent more time at rest during the longer days of this season. In other words, they appeared to adopt a “time-minimizing foraging” strategy, rather than an “energy-maximizing” one, as indicated by the traditional time budgets. The study indicates that manipulation of the duration of the daily activity period may be an integral component of the foraging strategies of some primate species, and that this needs to be taken into account for the analysis of behavioral data.
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