Ecology of burrowing bettongs, Bettongia lesueur (Marsupialia: Potoroidae), on Dorre and Bernier Islands, Western Australia

Abstract

Population structure, reproduction, condition, morphology, movements, habitat preference, and dynamics of the burrowing bettong were assessed on Dorre and Bernier Islands between 1988 and 1995. The data come from 982 captures of bettongs in 2661 trap-nights (an average of 37 captures per 100 trap-nights). Recaptures within a trip made up 39% of bettong captures. Bettongs were more abundant, as indexed by trap success, than were western barred bandicoots (the other species caught in considerable numbers on trapping grids). Sex ratio of bettongs (excluding recaptures) were skewed heavily towards males at 1.43: 1 despite approximate parity in pouch young. Production of young was concentrated in the wetter winter months and appeared to fall well below their theoretical capacity of 3 young per year. Bettong females were capable of producing young at 880–900 g (approximately 7–8 months of age) but incidence of females with pouch young or showing signs of recent lactation increased from 40% for females of 881–1000 g to 62% for females > 1000 g. The incidence of sub-adult bettongs in the population peaked in spring, but varied between years (range 0–14% of the population). There was an excess of males over females in the sub-adult population. Bettongs showed little sexual dimorphism but there were significant differences in morphology between the two island populations. Bettongs appeared to suffer substantial reductions in numbers in a prolonged drought extending from October 1986 to April 1989, reducing trap success for this species to 19% in the 1989 survey. Numbers grew strongly on both islands after the breaking of the drought in May 1989, showing an observed rate of increase of r = 0.75 on Dorre Island. Trap success had increased to 45% in September 1991. There was a high turnover of bettongs on trapping grids – 25–40% over 6 months to 80% over 3 years. Movements of bettongs appeared limited: the median distance moved by bettongs captured more than once within an 8-day trapping session was 160 m. Only 4% of recorded movements were greater than 1 km. There was no significant difference in movements between the sexes. Bettongs were widely dispersed in winter through the four habitats surveyed but tended to concentrate in dune and Triodia sandplain habitat in autumn and spring.