Effect of Group Size on Activity Budgets of Colobus vellerosus in Ghana
Primate activity budgets are dictated by food availability and distribution, thus primates living in seasonal environments must adapt their behaviors to accommodate fluctuations in Int J Primatol (2017) 38:613–622 DOI 10.1007/s10764-017-9954-0 The online version of the original article can be found under doi:10.1007/s10764-016-9923-z. * Rebecca Hendershott Rebecca.Hendershott@anu.edu.au 1 School of Archaeology and Anthropology, Australian National University, Acton, ACT 0200, Australia 2 Fauna & Flora International’s Vietnam Programme, Hanoi, Vietnam resources. Cat Ba langurs (Trachypithecus poliocephalus), a Critically Endangered Asian colobine and a member of the limestone langur group (francoisi superspecies group within genus Trachypithecus), live only in fragmented and disturbed habitats on Cat Ba Island, northeastern Vietnam. This study aimed to assess the behaviors and diet of Cat Ba langurs by group, age, sex and season.We predicted theywould have high proportions of inactivity and foraging, low proportions of social behaviors, with seasonal variation that reflects an energymaximising strategy.We conducted behavioral observations through scan sampling over an 11 month period and found that Cat Ba langurs spent a significant portion of their day inactive (55 ± 1.3%) followed by foraging (19 ± 1.1%), locomoting (12 ± 0.9%), engaging in social behavior (12 ± 0.7%), and engaging in ‘other’ behaviors (2 ± 0.2%). Their diet was made up primarily of leaves (84 ± 2.8%) followed by fruit (8 ± 2.8%), flowers (5 ± 1.7%), and stems (3 ± 1.2%). Activity budget differed between groups, which is likely due to differences in demographics and home range between groups. Seasonally, the animals ate more leaves and spent more time foraging in the dry season than the wet season, suggesting that they are energy maximisers. Cat Ba langurs have similar activity and dietary budgets to other limestone langurs, and respond to a presumed seasonal fluctuation in food availability similarly. Statistical Analysis: We calculated activity and dietary budgets based on 541 contact hours, across 180 days of observation spanning 11 months in the field (Table II).We calculated daily activity budgets as the proportion of scans that included each specific behavior category and daily dietary budgets as the proportion of feeding records that included a specific dietary item. Following similar studies (Teichroeb et al. 2003; Hu 2007; Zhou et al. 2007) we treated days as independent data points. To assess whether activity or dietary budgets vary with season, group, age, and sex, we fitted separate linear models with arcsine transformed proportions of daily behavior or food items eaten as the dependent variable. The independent factors were (i) behavior or food, and (ii) age, sex, group, or season (each in a separate model), and the interaction between the two. If we found that the overall activity or dietary budget differed significantly by age/sex/group/season, we assessed the differences between categories for each behavior or food item separately using a binomial logistic model, accounting for overdispersion. As we found no significant interaction effect of (season) x (behavior or food) x (age, sex, or group), we pooled groups for seasonal analysis. We removed newborns from all analyses because their behaviors were non-independent. While the foraging category included water drinking (N=26), we did not analyse this as part of the dietary budget. We used SPSS 23 for Windows for all analyses, with significance set to P<0.05 for two-tailed tests. Results: Overall Activity and Dietary Budget Of a total of 10,879 scans in which we identified behavior (excluding newborns), inactivity was the most common behavior, occupying a mean of 55 ± 1.3% of the daily 614 R. Hendershott et al.