Timing of breeding and female fecundity of the greater bilby (Macrotis lagotis) in the temperate zone of South Australia: implications for translocations of a previously widespread species

Context: Many of Australia’s threatened mammals were once widespread across the continent and present in both arid, semiarid and temperate habitats. However, data on breeding biology can be lacking for some climatic regions due to local extinctions of populations. The breeding biology of the greater bilby (Macrotis lagotis) has previously only been studied in captive colonies or free-ranging arid zone populations. Between 1997 and 2005, captive-bred bilbies were released at two sites in temperate South Australia. These populations provided an opportunity to determine whether bilbies adopt a seasonal reproductive strategy in the temperate zone, where this species has not been present since the early 1900s. Aims: To determine the season of births, litter size and female reproductive potential in two free-ranging populations of the bilby in the temperate zone of South Australia. Methods: Bilbies were regularly cage-trapped at Venus Bay Conservation Park and Thistle Island between August 2007 and April 2010 to obtain data on reproductive activity in both populations. Key results: Births of pouch young in both populations occurred in winter (June–August), spring and early summer, but not between February and mid-May. Males had a significantly smaller mean testes size relative to head length in late summer, when breeding activity ceased. Average litter size at pouch emergence was between 1.00 and 1.47 pouch young, with females producing up to three litters per annum. The mean head length of females that successfully raised twins was significantly larger than that of females who raised a single pouch young. Conclusions: The seasonal breeding pattern observed in the present study differs from that of year-round reproductive activity in captivity and the arid zone. The present study suggests that female body size influences fecundity, and that releasing large females at the start of the breeding season in temperate areas may maximise the initial rate of increase of a translocated bilby population. Implications: The present study suggests previously widespread species such as the bilby can adapt their reproductive strategy to suit local conditions. Cessation of breeding in autumn, as observed in this study, has also been observed in other bandicoot species in southern Australia.

Karleah K. Berris, Steven J.B. Cooper, William G. Breed and Susan M. Carthew