Inter-male aggression in relation to female availability and residence status in corn mice Calomys musculinus

Abstract

We conducted an experimental study to test the hypothesis that at low female availability males show intra-sexual aggressive behaviour and home range owners are more aggressive than home range intruders. Using field dyadic arena test we carried out 35 male-male trials in four 0.25 ha enclosures, two male-biased (experimental enclosures), and two unbiased (control enclosures). Dyadic encounters were conducted between un-related and sexually mature males of similar weight and age which established home ranges in the same enclosure at the same trapping session. Each inter-male encounter was performed in the home range of one of the opponents between the home range owner and a home range intruder. When sex ratios were male-biased, inter-male amicable behaviour was absent and we found significant rates of inter-male aggressiveness, being home range owners much more aggressive than intruders. In the unbiased enclosures inter-male encounters resulted mainly in non-interactive or amicable interactions.We found that inter-male aggression varied in relation to female availability being more evident in home range owners.