REPRODUCTIVE-BIOLOGY OF THE FERAL HOUSE MOUSE (MUS-MUSCULUS) ON SUB-ANTARCTIC MACQUARIE ISLAND

Reproduction of the feral house mouse (Mus musculus) was studied on su bantarctic Macquarie Island and found to be seasonal. Females begin oe strus-cycling in early spring, following a minimum 3-month winter anoe strous period. By late spring all mature females are in breeding condi tion. Breeding is continuous through spring, summer and into autumn. P ostimplantation loss occurs throughout the breeding season. Late autum n pregnancies may fail. Average litter size is 6-7 but litters as larg e as 10 have been found. Young born in the latter half of the breeding season attain sexual maturity at a later stage than those born in the early-spring-summer period and do not come into breeding condition un til the following spring. Males show a slight cyclical change in teste s weight, increasing from a winter minimum to a summer maximum, but ar e potentially capable of breeding throughout the year. Reproductive se asonality of the female determines breeding behaviour in this isolated subantarctic population of feral house mice. Seasonal reproduction is not well correlated with mean monthly ambient temperature, which vari es by only 3-degrees-C over the year. Food availability appears consta nt throughout the year with little interspecific competition for food or predation on the mice. Reproduction is suppressed over the short-da y winter months. The possible interaction of photoperiod with other en vironmental and physiological variables in determining reproductive se asonality requires further research.