The Spatial Behaviour of Indri indri

Quantitative descriptions of animal movement patterns and accurate home range estimates are important for the understanding of a species’ spatial and behavioural ecology. Here, we illustrate home range size estimations and ranging behaviour of 12 groups of indris (Indri indri) inhabiting three different forest sites near Andasibe (Madagascar): the Réserve Spéciale Analamazaotra, the Station Forestière Analamazaotra (Mitsinjo forest) and the Maromizaha forest. A period of 14 months was spent between 2005 and 2010 collecting spatial data and information about group composition. We examined home range size, ranging behaviour and interactions between neighbouring groups, in order to increase knowledge of indri social interactions and territorial behaviour. Using the MCP (100%) method, home range size estimations varied from 6.29 ha to 26.95 ha (mean value of 14.46 8 5.47 ha), whereas the mean daily path lengths corresponded to 287.16 8 145.74 m and ranged from 149.44 to 397.90 m. We found a correlation between home range size and group size, which is presumably influenced by various factors such as availability of food, resources distribution and defendability of the territories. We found that indri groups defended their territories from intruders, and overlap between neighbouring groups did not occur. Inter-group encounters at the boundaries were relatively rare, supporting the hypothesis that the indris’ song is effective in maintaining spacing between adjacent groups.