Ecology of the rare but irruptive Pilliga mouse ('Pseudomys pilligaensis'): II. Demography, home range and dispersal

We report aspects of demography, home range and movement of the rare Pilliga mouse, 'Pseudomys pilligansis', during a population irruption, peaking in April 2000, and the subsequent decline. Population median weights were lower before than at, or after, the irruption peak. Individual mice grew more strongly immediately before the peak than later. The initial weight negatively influenced the growth rate, more so at the irruption peak than before it. At peak, mice at previously occupied sites were heavier than those at recently occupied sites, and male-biased, compared with the female-based mice dispersing into new sites. The population at the most densely occupied site was strongly female-biased just before and at peak; female dispersers tended to survive better than males. After the irruption, residents survived better than the newly established mice at the only site that retained moderate densities. Individual movements mostly did not differ between sexes, or among sites or size classes. Range overlap, more extensive in spring breeding in a non-territorial population, with rapid individual growth, and led to dispersal especially by a female-biased subpopulation of lighter (and perhaps younger) mice. After the irruption peak, the rapid growth in weight stopped, suggesting resource restriction, and the social system may no longer have been non-territorial.