Ecology of the western barred bandicoot (Perameles bougainville) (Marsupialia: Peramelidae) on Dorre and Bernier Islands, Western Australia

Abstract

Population structure, reproduction, condition, movements and habitat preference were assessed for western barred bandicoots (Perameles bougainville) on Dorre and Bernier Islands over seven trapping sessions between 1988 and 1995. Data comes from 372 captures of bandicoots in 2535 trap-nights (an average of 14·7 captures per 100 trap-nights). Trap success was 5.7–25.8% on Dorre and 5.7–7.6% on Bernier. Recaptures within a trip made up 29% of bandicoot captures. The overall sex ratio (excluding recaptures) was skewed heavily towards males at 1.7: 1 for trapped animals, but varied between male and female dominance at any time according to reproductive status of females. Sex ratio of pouch young was 1.2: 1. Production of young was concentrated in the wetter winter months. The smallest western barred bandicoot with pouch young weighed 175 g. Bandicoots showed a pattern of increasing litter size with size of mother. Females with young had an average litter size of 1.8, with young reaching independence at about 100 g body weight. Large testes size relative to body size in males suggested a promiscuous mating system. Body condition could be predicted by sex (females were typically in better condition than males) and by rainfall over the previous 2 months. Some sexual dimorphism was evident, with females having longer heads and typically being heavier than males. There was no detected dimorphism between island populations. Movements of bandicoots appeared limited, with the median distance moved by animals captured more than once within a 9–11-day trapping session being 154 m. There was no significant difference in movements between the sexes, with males moving a median distance of 160 m and females 138 m within trapping sessions. The greatest movement by a male was 1020 m while the greatest distance moved by a female was 490 m. Only 13% of recorded movements were greater than 400 m. Home ranges overlapped, with 51% of traps catching more than one individual and as many as five males being caught at the same trap site. Bandicoots were widely dispersed through all habitats surveyed. Bandicoots appeared to suffer a substantial reduction in numbers on Dorre Island in a prolonged drought extending from October 1986 to April 1989, reducing overall trap success to less than 6% in the 1988 survey.