Australia’s small arid zone mammals have greatly suffered since European settlement. Some 11 species are extinct, and a further eight are listed as endangered or critically endangered. Their loss has been attributed to both the change in land management, and the introduction of pest species.
The Central Rock-rat (Zyzomys pendunculatus) is one of five species of rock rats, and the only one that lives in the arid zone. It, together with the Carpentarian Rock-rat (Zyzomys palatalis), is listed as critically endangered on the IUCN Red List.
It is physically very similar to the other species of rock-rat, but differs in its more heavily furred tail and relatively longer ears. Like its relatives, it has been recorded in a range of rocky habitats including granite boulder fields, quartzite ridges and eroded sandstone cliff-lines.
The Central Rock-rat has been a rare species for a long time. Most museum specimens were collected during the 1894 Horn Expedition to central Australia, or in the flowing year. Two specimens were collected in 1952 in the northern Tanami Desert.
A lone individual was caught by a stockman in 1960 as it raided his tucker box near Mount Liebeg, 300km west of Alice Springs. It wasn’t seen again until 1996, when a population was discovered in West MacDonnell National Park.
A peak in numbers occurred in 2000 following high rainfall, however the population crashed after dry conditions and massive wildfires in 2002.
In a massive trapping effort from 2009 to 2011, only four individuals were caught in one of 42 sites surveyed. The same number were captured from 2011 to 2012.
The disappearance of the Central Rock-rat from much of its former range remains a mystery. Even though the 2002 wildfire burnt 60% of the West MacDonnell National Park, most of the previous monitoring sites were unburnt.
Foxes, which have been attributed to decline of many arid zone mammal species, are rare in the National Park. Feral cats are common in the area, and perhaps contributed to the decline when food and shelter were sparse.
It is likely that the combination of predators, fire and climate all play a role reducing the rock-rat numbers. The slow regeneration rate of the local vegetation after the 2002 wildfire could explain why the rock-rats did not recover in number after the high rainfall in 2010 to 2011.
Due to the uncertainty in what drives the population dynamics and distribution of this species, further targeted research is required.
There is an existing prescribed burning program in the National Park which aims to reduce the threats of wildfire.
Controlling cats at the scale required to be effective has proven to be difficult. But some strategic baiting at appropriate times may be effective. Baiting, however, should not impact on local dingo populations, which have been demonstrated to assist small mammals by controlling foxes and cats.
While it is encouraging that the Central Rock-rat still persists in parts of its range, it is also of extreme concern that the populations appear very small. It is also disconcerting that the reasons for its decline are still uncertain. Without continual monitoring and targeted research, another of Australia’s unique arid-zone mammals may become extinct.
This article was written with help from Peter McDonald, who is a Senior Technical Officer for the Flora and Fauna Division of the NT Department of Land Resource Management.
The Conversation is running a series on Australian endangered species. See it here.