Bridled nailtail wallabies are medium-sized (3-8kg), solitary, nocturnal macropods. They were once widespread in eastern Australia, but now persist in the wild at only one locality in central Queensland (Taunton National Park). They use shrubs, grass, or hollow logs as diurnal shelters, and eat forbs grass, and browse. I used radiotelemetry, mark-and-recapture methods, and spotlighting transects to study behavioural ecology, life history and demography at two study sites within Taunton National Park in 1994-1997. The study began with 14 months of severe drought, but conditions improved over the subsequent two years. The two study sites were ~5km apart. Site one was dense forest regrowth and pasture, while site two was a mosaic of open woodland, mature forest and open swamp.
In chapter one (general introduction and methods), I describe the historical decline of bridled nailtail wallabies, general biology and methods. Chapters two to six address maternal investment and offspring sex ratio, mating system, juvenile antipredator behaviour and maternal care, shelter selection and influences on home range size, and survival and population dynamics. In the final chapter, I report general conclusions and management implications. Collaborative projects on genetic structure and dispersal, and on the effects of age, site and drought on the diet are reported in an appendix.
Adult wallabies of both sexes were significantly larger at site two. In females, this size difference was associated with better body condition and male-biased birth sex ratios. Sex ratio variation was most consistent with the Trivers-Willard hypothesis, but could also have been influenced by local resource competition, since sons dispersed further than daughters. Maternal and juvenile condition were positively correlated, but mothers did not bias investment in favour of one sex, except via sex ratio adjustment.
The mating system at site one was assessed with a collaborative microsatellite analysis of paternity. Competitive ability of males was related to body size, and was the most important predictor of the number of offspring sired by individual males. Male home range size was also a significant component of reproductive success. Females incited further competition between males by engaging in 'mate chases' and increasing their home ranges at oestrus.
Bridled nailtail wallabies have a 'hider' strategy of maternal care. After they had left the pouch permanently, juveniles spent the day concealed alone in dense vegetation, preferring small shrubs for shelter. They were also often apart from their mothers at night. Mothers with juveniles at this stage reduced their home ranges, stayed closer to cover and became more wary. Juveniles attempted to avoid detection by standing still or lying prone on the ground, which may have made them particularly vulnerable to predation. Predation by feral cats was the major cause of death.
Males had larger home ranges than females, but total home ranges size did not differ between sites. Total home range size tended to be inversely related to food availability. Site one had a much higher density of shelter, but had a similar density of food to site two. Wallabies at site two had much smaller diurnal home ranges. Diurnal home range size was correlated with grass biomass, because wallabies expanded their diurnal ranges to use more grass for shelter when it was available. Adults strongly preferred hollow logs over other types of shelter when they were available, and I investigated the effects of shelter density experimentally by providing 100 hollow logs at site two in late 1995. Wallabies used the shelter consistently, but any effect on habitat use was obscured by a large increase in grass biomass there during 1996.
Adult survival was related to individual health, but did not differ between years, sexes or sites, and was not related to food biomass, rainfall, or dingo activity, although dingoes were responsible for half of all deaths of radio-tagged adults. Population estimates were 41 to 83 at site one, and -13 at site two. Estimates tended to be negatively biased because of high heterogeneity in capture and sighting probabilities, and variation in habitat use with respect to the transect lines over time. Females had a very high reproductive rate of 3 young per year. Juveniles had lower survival rates (47%) than adults (80% a year), early pouch young (93%), and late pouch young (82%). A matrix modelling approach based on these values indicated that the population was increasing during the study, at 28% a year. The population rate of increase (k) was relatively most influenced by adult survival (elasticity for adult survival was 0.8). The body size difference between the two study sites was consistent with both a difference in individual growth rate, and with a difference in age structure.
The pattern of sex allocation, the mating system, and general spatial organisation of bridled nailtail wallabies all conform to the general pattern found in other macropods. The pattern of age-specific mortality in bridled nailtail wallabies is also similar to that of other species. Their small body size also has important effects on the maternal care strategy, antipredator behaviour, mating system, habitat use and life history. Survival at Taunton may be increased by using a strategy that combines cat and dingo control with vegetation management to promote shelter near feeding areas, especially during droughts.