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

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.

The effects of pre- and early post-calving management on reproductive performance of beef cows

One hundred and thirty-four pregnant beef cows (liveweight = 544.3 kg ± 73 3 kg SD; condition score = 3.5 ± 0.3 SD), were randomly assigned in January to five management treatments (combinations of feed restriction and weaning time) to study the effects on calving and rebreeding performance. Twenty-seven were feed-restricted (54.7 MJ DE d−1) for the last 3 mo of pregnancy then realimented (3REST); their calves were weaned in October. Thirty were feed-restricted for the last 3 mo of pregnancy (54.7 MJ DE d−1) and the first 2 mo of lactation (99.6 MJ DE d−1), then their calves were weaned and turned out to graze in June (5REST). The remaining 77 cows (UNREST) were supplemented on range with 153.5 MJ DE d−1 from January until calving. Their calves were weaned in either August (one group of 26 calves directly into a feedlot, a second group of 26 onto unsupplemented range) or October (25 calves directly into a feedlot). All cows grazed together on the range from June onwards. After calving, the restricted (3REST and 5REST) cows were significantly lighter (464.4 and 469.5 kg vs. 506.9 kg) and thinner (condition scores 2.5 and 2.6 vs. 3.0) than the UNREST cows, but the percentage of cows calving calf mortality, assisted births calving dates, udder scores and mean birth weight of calves were not affected (P > 0.05) by pre-calving nutrition. Catch-up growth was evident in both the 3REST and 5REST cows once exposed to higher energy feeding. There were no significant effects (P > 0.05) of the management (nutrition and weaning) treatments on the following year s breeding and calving performance. It is concluded that the combinations of nutrition and weaning used in this study did not necessarily impair calving or rebreeding performance of beef cows, which calved in condition score 2.5 or above. Key words: Beef cows, feed restriction, reproduction, condition score, rebreeding, birthweight