Observations on Body Weights and Breeding of the Northern Brown Bandicoot, Isoodon macrourus, Trapped in South-East Queensland

Abstract

Information on body weight, measurements and breeding is recorded for 96 female and 42 male Isoodon macrourus, trapped in the vicinity of Brisbane. Data are also given on sex ratio, nipple attachment site and mortality for 128 pouch young from 44 litters. I. macrourus is the heaviest peramelid, with a mean body weight of 1046 ( ± 263)g for females and 1496 ( ± 359)g for males. Seasonal effects on body weight are evident in females but absent in males. Females with pouch young were significantly heavier than those without young for most months of the year. Unlike most other peramelids, I. macrourus has no defined breeding season in south-eastern Queensland. Females produce litters in all months of the year, with a peak in August and a low in June. Litter size averaged 2.9, which is the lowest recorded for the species. Female body weight had a positive linear relationship with litter size (y= 0.001297x + 1.444). Sex ratio of adults was 1:1, but that of pouch young favoured males 1:0.8. Of the eight pouch teats available, young favoured the four anterior nipples (72 v.56) and males outnumbered females on the left-side nipples. Survival rate of pouch young, as indicated by litter size from 0 to 50 days, showed no variation but there appears to be a high mortality for young after they leave the pouch and before they reach a body weight of 500 g.