Effects of vegetation structure, food and shelter on the home range and habitat use of an endangered wallaby.
Abstract
Bridled nailtail wallabies Onychogalea fraenata are medium-sized, nocturnal, solitary macropods that persist in only one conservation reserve in central Queensland, Australia. They use shrubs, grass and logs as diurnal shelters. Factors affecting shelter choice, habitat use and home range size were interpreted in terms of habitat management, and shelter provision was assessed as a potential management tool. Shelter selection, food and variation in cover were assessed at two sites that differed in vegetation density and population density. In order to determine how habitat quality and potential visibility to predators affect ranging behaviour, the relationships among home range size, grass biomass, sex, site, habitat edge availability and moon phase were determined for 37 radio-collared wallabies during and after a severe drought. Open habitats contained more food, whereas wooded habitat contained more preferred shelter. Shelter but not food availability differed between the sites. Wallabies used a higher proportion of wooded habitat, and increasingly avoided open areas, as food biomass in wooded areas increased after the drought. Home range size differed between the sexes but not between the sites. It tended to be inversely related to availability of food and habitat edge. Diurnal home range size was correlated with grass biomass and was larger at the site with the lowest population density and lowest availability of cover, but it did not differ between sexes. A preference for habitat edges may reflect shelter quality. Animals chose shelter sites with the densest cover at wallaby height; cover was densest at this height at the forest edge. Wallabies used individual shelters repeatedly, were faithful to diurnal range areas, but did not appear to share shelter sites. They used experimentally provided shelter extensively, and more frequently than other medium-sized mammals at the sites. Increasing natural grass cover was associated with diurnal home range shifts and expansion, but experimental shelter provision had no effect on diurnal range size or location. Shelter did not explain differences in diurnal range size between the sites, which may instead be related to population density. Neither vegetation type was obviously better habitat. Ongoing large-scale manipulation of forest regrowth may be needed to increase habitat edges and maintain vegetation at the optimum height to provide shelter and food. Patchy clearing is therefore a potential strategy for habitat management for this species and other medium-sized forest-dwelling mammals.