Abstract
Aggressive encounters may have important life history consequences due to the potential for injury and death, disease transmission, dispersal opportunities or exclusion from key areas of the home range. Despite this, little is known of their detailed dynamics, mainly due to the difficulties of directly observing encounters in detail. Here, we describe detailed spatial dynamics of inter-pack encounters in African wild dogs (Lycaon pictus), using data from custom-built high-resolution GPS collars in 11 free-ranging packs. On average, each pack encountered another pack approximately every 7 weeks and met each neighbour twice each year. Surprisingly, intruders were more likely to win encounters (winning 78.6% of encounters by remaining closer to the site in the short term). However, intruders did tend to move farther than residents toward their own range core in the short-term (1 h) post-encounter, and if this were used to indicate losing an encounter, then the majority (73.3%) of encounters were won by residents. Surprisingly, relative pack size had little effect on encounter outcome, and injuries were rare (<15% of encounters). These results highlight the difficulty of remotely scoring encounters involving mobile participants away from static defendable food resources. Although inter-pack range overlap was reduced following an encounter, encounter outcome did not seem to drive this, as both packs shifted their ranges post-encounter. Our results indicate that inter-pack encounters may be lower risk than previously suggested and do not appear to influence long-term movement and ranging. Direct aggressive encounters between competitors are an important and potentially dangerous aspect of territoriality. In spite of this, detailed data on movements in response to encounters are lacking, especially for large mammals. Collecting observational data on competitors leaving an encounter site in different directions is logistically challenging, and radiocollar technology has previously been ineffective in this regard due to low temporal resolution. We overcame these issues by using custom-built high-resolution GPS collars, showing that intruding African wild dog packs were more likely to win inter-pack encounters (residents initially moved further away from the encounter). Inter-pack encounters appeared to have only short-term impacts on movement, with their outcome having no discernible impact on the long-term ranging patterns of African wild dog packs.
Highlights
Inter-group encounters may have important life-history consequences, due to the potential for injury and death, disease transmission (Craft et al 2011), information exchange and dispersal opportunities (Sicotte 1993), or exclusion from important areas of their previous range (Ewing 1972)
There may be considerable costs to direct inter-group encounters, relatively little is known of the detailed dynamics of these events
In particular literature from social birds, primates and carnivores suggests that relative group size is important in determining encounter outcomes
Summary
Inter-group encounters may have important life-history consequences, due to the potential for injury and death (e.g. gray wolf Canis lupus, Mech 1994; Cassidy et al 2015; chimpanzee Pan troglodytes, Townsend et al 2007; yellow baboon Papio cynocephalus, Shopland 1982), disease transmission (Craft et al 2011), information exchange and dispersal opportunities (Sicotte 1993), or exclusion from important areas of their previous range (Ewing 1972). In particular literature from social birds, primates and carnivores suggests that relative group size is important in determining encounter outcomes (e.g. green woodhoopoe, Phoeniculus purpureus, Radford and du Plessis 2004; chimpanzee, Wilson et al 2001; black howler monkey, Alouatta caraya, Kitchen 2004; banded mongoose, Mungos mungo, Rood 1975; Furrer et al 2011). As the benefits of winning a contest may vary according to where it occurs within the territory (e.g. Maynard-Smith 1982), location has been shown to affect encounter outcome in some species (e.g. banded mongoose, Furrer et al 2011, but see Rood 1975; chacma baboons, Papio cynocephalus ursinus, Kitchen et al 2004; Verreaux’s sifaka, Propithecus verreauxi, Koch et al 2016,) but not in others (e.g. chimpanzee, Wilson et al 2001; black howler monkey, Kitchen 2004). Similar patterns have been reported for gray wolves, where packs with more males or older individuals than their rivals were more likely to triumph in encounters (Cassidy et al.2015)
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