Effects of sex and breeding status on habitat selection by feral House mice (Mus musculus) on a small Mediterranean island

Patterns of habitat use of the house mouse (Mus musculus) in relation to sex and breeding status were studied in April and May (the early breeding season) in two structurally different habitats on a small Mediterranean island in NE Spain. Overall mice abundance increased from bare and rocky areas to areas with a dense cover of shrubs and herbaceous plant. Females were associated to shrub areas in April. shifting towards more herbaceous areas in May. Males were less selective, being only slightly related to shrub height in April, and they were not associated with structural habitat features in May. Overlap in habitat use by sexes existed in both months being more reduced in April than in May. Female densities were significantly higher in the habitat with dense vegetation cover (suitable habitat) than in the habitat with scarce vegetation in both months, while densities of males were not. Male density decreased from April to May in the suitable habitat, and intersexual competition was exclusively detected in the period of higher male density in this habitat, intraspecific competition explained the spatial distribution of sexes regardless of habitat structure characteristics In absence of competition the spatial distribution of sexes was mainly related to habitat structure. Females and males started sexual activity early in the season in the suitable habitat. Weight of females was higher in suitable habitat in both months, also showing a positive association with the herbaceous cover, and the average weights of males and females at trapping stations were positively associated. Our results are finally discussed in relation to the social organisation models proposed for house mouse populations.