A comparison of scan and focal sampling for the description of wild primate activity, diet and intragroup spatial relationships.

We used data collected during two concurrent studies of black howler monkeys (Alouatta pigra) in Palenque National Park, Mexico, to compare systematically three methods of behavioral data collection [group activity scan sampling (group scans), instantaneous focal individual sampling (instantaneous focals) and continuous focal individual sampling (continuous focals)] and three methods of proximity data collection [group proximity scan sampling (group proximity scans), focal individual proximity scan sampling (focal proximity scans) and instantaneous focal individual nearest neighbor sampling (focal nearest neighbor samples)]. We conducted pairwise comparisons of data among methods using Pearson correlations and one-sample t tests. A series of Kruskal-Wallis tests were performed to compare the activity and proximity patterns of adult males, adult females and juveniles described by each method. The three behavioral data collection methods generally provided similar information about activity and diet. However, important differences for both activity and proximity data existed among methods. Instantaneous focals overestimated the percentage of time spent in social interactions, while group scans overestimated time spent moving and underestimated time spent feeding. Group proximity scans and focal proximity scans provided similar spatial data, while focal nearest neighbor samples were more appropriate for determining the influence of one individual on another at any given moment. These biases suggest the importance of deliberate method selection during project design and highlight the need for taking methods into account when comparing studies.