Population density of the mantled howler monkey (Alouatta palliata) at La Selva Biological Reserve, Costa Rica: a new technique to analyze census data

Using an agglomerative hierarchical clustering method to estimate minimum number, the estimate of 15 troops (7-15 howlers/km²) is similar to an independent census of the same population using the triangulation technique. Cluster analysis has several advantages over more traditional primate census techniques: the assumption that it is necessary to achieve reliable estimates from line transect sampling is not required; census data can be collected by one person; census data collected over a brief period of time can be used to provide quantitative estimates of population density; and observations provided by others in the survey area during the time period of the census may be used. Cluster analysis is recommended when attempting to estimate population densities of primates in tall evergreen forests where visibility is poor, when animals have long inactive periods, few or unpredictable vocalizations, and/or occupy the top of the canopy. -from Author