Abstract
Territorial, socially monogamous species actively defend their home range against conspecifics to maintain exclusive access to resources such as food or mates. Primates use scent marks and loud calls to signal territory occupancy and limit the risk of intergroup encounters, maximizing their energetic balance. Indri indri is a little-studied territorial, socially monogamous singing primate living in family groups. The groups announce territory occupancy with long-distance calls, and actively defend their territories from conspecific intruders. This work includes data collected in three forests in Madagascar on 16 indri groups over up to 5 years. We aimed (1) to estimate the extent of territories using minimum convex polygon (MCP), implementing minimum sampling effort requirements; (2) to quantify territorial exclusivity, measuring the overlap between territories; and (3) to evaluate the intergroup encounter rate and to quantify the dynamics of group encounters. Our results showed that indris range evenly within exclusive small territories with no or little overlap. Intergroup encounters are rare (0.05 encounters per day), and are located on the periphery of the territories. Disputes were mostly solved with vocal confrontation and only in 13% of the cases ended in physical fights. This frame underlines a cost–benefit explanation of territoriality, favouring a strategy that efficiently limits overlap and avoids costly intergroup encounters. We hypothesize that territorial behaviour in indri is related to mate-guarding strategy and that vocal behaviour plays a fundamental role in regulating intergroup spacing dynamics.
Highlights
A territory is an area occupied by an individual or a group, actively defended against conspecifics to maintain exclusive access to resources, usually food or mates (Burt 1943)
We considered the seven selected data sets big enough to give a reliable estimate of territory size with MCP100, and we compared territory size estimates based on the entire number of the sampling days respectively with: 3. MCP100 and the randomizations (MCPr): the territory size was the estimates at 100% of the territory obtained with randomization of daily data sets
Mitsinjo) recorded in 2008, during 13 successive days at Mitsinjo, we found evenly distributed tracks between the centre and the minimum convex polygon (MCP) boundaries such that a group takes 2 weeks to range in the whole territory (Figure 2)
Summary
A territory is an area occupied by an individual or a group, actively defended against conspecifics to maintain exclusive access to resources, usually food or mates (Burt 1943). Spatial behaviour and intergroup relationships vary widely among Primates as they are determined by taxon-specific ecological, physiological and social requirements (Jetz et al 2004). A clear understanding of the mechanisms underlying this variability is important because both spatial and intergroup behaviours represent important determinants of mating system as well as of population density and growth rate (Lazaro-Perea 2001; Glessner & Britt 2005; Spencer 2012).
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