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

Abstract

Activity budgets are widely used in primate behavioral studies for the analysis of ecological strategies. In some cases, there is considerable seasonal variation in the length of the daily activity period. Here, activity budgets from two field studies of Callithrix flaviceps were compiled first by the traditional approach (proportion of scan sample records) and then by considering the proportion of time dedicated to each activity over the 24-hr cycle (adjusted budget). Both groups were almost invariably active for at least 1-2 hr less than the daylight period, with significantly shorter activity periods during the austral winter, when the daylight period was up to 2:35 hr shorter than in the summer. The adjustment of activity budgets provided a completely different perspective on foraging strategies. Whereas the basic budgets indicated a significant increase in foraging and moving during the resource-poor dry season (winter) months, the time-adjusted data revealed that the primary strategy was a time-minimizing one, with the animals simply spending more time at rest during the longer activity periods of summer days. While both groups followed the same pattern of relatively short activity periods, there were considerable differences between sites in the mean duration of the period in a given month, and in behavior patterns, although the analysis of the determining factors was beyond the scope of the present study. Overall, the results of the study indicate that the manipulation of the duration of the daily activity period may be an integral component of primate behavioral strategies, and that this parameter should be taken into account systematically when evaluating activity patterns, especially at sites at relatively high latitudes where day length may vary considerably over the course of the year.

Nutrition and foraging strategies of the black howler monkey (Alouatta pigra) in Palenque National Park, Mexico

“…The behavioral data were used to calculate the average percentage of time the howlers spent in a given activity during a focal sample in each season. Because howler monkeys are active during all daylight hours, the average day length during each of the three seasons was used to calculate the average number of minutes per day the howlers spent in each activity [see Ferrari & Hilario, ]. Average ingestion rates for each plant part from each plant species, as well as average food item masses, were used to estimate the average number of grams of each food item ingested daily by each individual during each week, month, and sampling block.…”

Food availability, plant diversity, and vegetation structure drive behavioral and ecological variation in Endangered Coimbra‐Filho's titi monkeys

“…We calculated the activity budget by considering the percent contribution of each behavior's scan sample records (p i ) and then estimating the mean duration of each behavior using t i = p i × T, where T is the mean duration (in minutes) of the daily activity period (Ferrari & Hilário, 2014). We converted the t i values to adjusted percentages (ap i ) by ap i = t i /1440 × 100, where 1440 is the number of minutes in a 24-h period.…”

“…We converted the t i values to adjusted percentages (ap i ) by ap i = t i /1440 × 100, where 1440 is the number of minutes in a 24-h period. We used this approach because the duration of the daily period may be an important component of primate behavioral strategies in relation to feeding resources (see more details in Ferrari & Hilário, 2014). We used the same calculations for activity budget as for diet to determine the percent contribution of the various plant species used as a food resource by the monkeys.…”

Temperature and exudativory as drivers of the marmoset (Callithrixspp.) daily activity period

“…Thus, the benefits of enforced resting to maintain body temperature must balance the costs of lost food consumption. In addition to daytime resting, sleeping is also part of the strategy of time allocation by primates (Ferrari & Hilário, 2014), which may reduce energy expenditure through physiological and/or behavioral mechanisms such as nighttime torpor (Vuarin et al, 2013) and huddling (Angilletta et al, 2010; Scantlebury et al, 2006).…”

“…As marmosets are diurnal, their activity period is limited to the daylight period (Ferrari & Hilário, 2014), and they typically become active just after dawn and cease their activities sometime before dusk (Castro et al, 2003; Hilário, 2009; Suchi & Rothe, 1999). They are poor thermoregulators, with body temperatures varying in response to ambient temperature, which may affect their bodily functions (Morrison & Simões, 1962).…”