Does high growth rate of juvenile house mice with prolonged access to ripening grain and free water drive population outbreaks?

Abstract

Post‐weaning growth rates were measured for juvenile house mice (Mus domesticus) reared under four experimental treatments representing dietary conditions in cereal‐growing areas of southeastern Australia. The mice were bred in captivity from adult wild mice captured in mature dry cereal crops during summer. Juvenile mice were caged in pairs at 23°C and offered a diet of either ripening wheat heads or mature dry wheat heads, with or without access to free water. All diets were adequate for survival, but juvenile mice on a diet of ripening wheat with water available grew at 0.25 g day–1, 260% faster than those on a diet of mature wheat and deprived access to free water. Mice on a diet of ripening wheat but deprived of free water and those on a diet of mature wheat with water available grew at intermediate rates. Post‐weaning growth rates of mice in all treatment groups were higher when the young were weaned at higher body mass. The results have implications for estimates of growth, timing of sexual maturity and reproduction of mice in field populations, and indicate that prolonged access to ripening grain and/or relief from moisture stress are likely to be critical to rapid population increase during population outbreaks.