by Dr Catherine Hayes, Wildlife Ecologist
A four-year research project on the elusive Sharman’s Rock-wallaby (Petrogale sharmani) has just wrapped up at Australian Wildlife Conservancy’s Mount Zero-Taravale Wildlife Sanctuary, in northern Queensland. This project was a collaboration between AWC, the University of Queensland and the Queensland Department of Environment and Science.
The project was the first detailed ecological study of the threatened species, which has a highly restricted range between Townsville and Ingham in north Queensland. Most of the known colonies of the species occur on Mount Zero-Taravale. Sharman’s Rock-wallaby is nocturnal, spending the daylight hours hidden in rocky caves and crevices and coming out to forage at night. Its nocturnal habits and love of steep, rocky terrain makes it a very challenging species to study, but gathering baseline ecological information is critical for its future conservation management.
© Catherine Hayes/AWC
Population dynamics
Three sites on Mount Zero-Taravale were trapped repeatedly during the study to establish baseline data on the species’ population dynamics and reproductive ecology. Colony sizes were small (less than 15 animals), however, nearly all of the female rock-wallabies trapped carried pouch young, with most breeding to their full potential. These results suggest that although small, these populations are not at immediate risk of decline and have healthy reproductive rates. Nevertheless, with estimates of fewer than 700 animals in the entire global population, it is important to track the status of this species and ensure management of its habitat is appropriate.
The role of fire for conservation
The study highlighted the importance of AWC’s prescribed burning program in promoting food resources for Sharman’s Rock-wallaby, and in protecting its habitat from large wildfires. GPS collars were fitted to 15 rock-wallabies to track their movements around their rocky shelter sites. Their response to fire was also studied, as the GPS collars recorded the location of the rock-wallabies both before and after fire.
Like other herbivores, Sharman’s Rock-wallaby quickly made use of ‘green pick’ which flourished after fires. The rock-wallabies showed a strong preference for foraging in the recently burnt areas on the new grasses and forbs. At one site, they completely abandoned a slighter older burn scar (two months older) to forage on the newer burn.
The tracking allowed us, for the first time, to determine the home range of Sharman’s Rock-wallaby. The average home range was less than 10 hectares. They moved an average of 200 metres from their rocky shelter sites while foraging at night. The smallest collared female had a home range of under four hectares. These results highlight how closely tied these rock-wallabies are to their rocky shelter sites. In addition to promoting the rock-wallabies’ food plants, AWC’s prescribed burning program will also reduce the chance of intense and extensive late dry season fire destroying the entirety of the food resources at one or more colonies.
Predator monitoring
Over 17,000 camera trap nights were undertaken to better define the distribution of Sharman’s Rock-wallaby and to investigate how often feral cats and Dingoes were present at rock-wallaby sites. Dingoes were detected six times more frequently than feral cats over the course of the study. Cats and Dingoes were active at different times: cats showed a midnight activity peak, whereas Dingoes were more active at dawn and dusk. Both predators were detected more often on roads and in open habitat than in the rocky areas.
These results suggest that a healthy population of Dingoes is working to suppress feral cat activity, and possibly abundance. Dingoes are also likely to regulate the abundance of potential competitors of Sharman’s Rock-wallaby, such as Common Wallaroos (Macropus robustus).
Mapping rock-wallaby distribution
The study confirmed Mount Zero-Taravale provides vital habitat for Sharman’s Rock-wallaby. Six new colonies of Sharman’s Rock-wallaby were discovered during the study, meaning AWC protects 70 per cent of all the known populations of this species. Habitat modelling suggests there may still be undiscovered colonies on Mount Zero-Taravale. These steep, rocky sites will be targeted by AWC in future surveys of the species.
Modelling based on Sharman’s Rock-wallaby’s current range showed a huge reduction in potentially suitable habitat under climate change, with only several small pockets of suitable habitat predicted to remain by 2070. Importantly, Mount Zero-Taravale is predicted to play a crucial role in ensuring the survival of Sharman’s Rock-wallaby into the future.
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