The rediscovery of an “extinct” small mammal

In 1856 the Blandowski Expedition set out to document the natural history of the Murray Mallee region. The expedition collected over 30 species of native mammals and provided a remarkable record of Australia’s historical fauna.

Sadly, one-third of the mammals recorded in this area are regionally extinct. This is due to several factors: land clearing, grazing by introduced stock and rabbits, predation by cats and foxes, and inappropriate fire regimes.

A notable find by the Blandowski Expedition was a small rodent with rufous-brown hair. Naturalist Gerard Krefft wrote that the species was “found in large numbers” in the “Murray and Darling scrub”. Until recently the Desert Mouse had not been seen in the Murray Mallee for 150 years.

Tarawi Nature Reserve is located in the northern Murray Mallee. In early 2012, Ray Dayman from the National Parks and Wildlife Service was continuing his long-term surveys of small mammals in the reserve. In one of the pitfall-traps was a rodent with a prominent orange eye-ring. Another individual was captured in a follow-up survey (pictured here).

After 150 years the Desert Mouse was back.

The Desert Mouse. Indigenous Australian’s of the Murray Mallee knew it as “Pethack” or “Ramm Ramm”. Troughton described it as Pseudomys desertor in 1932. I prefer Ramm Ramm. Photo: Ray Dayman

But why now?

In 2011 Tarawi Nature Reserve received its highest rainfall on record. The reserve is located in semi-arid Australia and the vegetation is dominated by mallee eucalypts and spinifex. In these dry landscapes, high rainfall often results in pulses of primary productivity. This means more food for rodents such as shoots, seeds and invertebrates.

Many arid-zone rodents have life histories geared to take advantage of these good times: they can produce multiple litters per year, they have a short gestation period, and they can reach maturity relatively quickly.

The Desert Mouse is no exception. In areas where it’s more common, such as in central Australia,  good rains have been followed by a 24-fold increase in capture rates of the species.

Two other rodents occur at Tarawi Nature Reserve: the endangered Bolam’s Mouse and the introduced House Mouse. In 2011, I captured record numbers of both species within the reserve.

Annual rainfall at Tarawi Nature Reserve (1967-2011). Lines are the median, the 90th percentile, and the 10th percentile. The record rainfall of 2011 is circled.

So, the rediscovery of the Desert Mouse is probably linked to rainfall-driven changes in population numbers. This is consistent with recent population booms of rodents across much of the arid-zone.

But there are a few things we don’t know. The nearest known population of the Desert Mouse is in Sturt National Park, over 400 km away. Are there closer populations? Has the Desert Mouse been present in the Murray Mallee region this whole time? What refuges have helped to maintain or reconnect populations? What role has the management of introduced predators, herbivores and fire regimes played?

It’ll be fun finding out.

What we do know is that long-term surveys – such as those completed by Ray Dayman and NPWS – provide valuable insights into the determinants of animal distribution and abundance.

References.

Bennett, A.F., Lumsden, L.F, & Menkhorst, P (2006) Mammals of the Mallee Region, Victoria : past, present and future. Proceedings of the Royal Society of Victoria, 118, 259-280.

Krefft, G (1866) On the vertebrated animals of the lower Murray and Darling, their habits, economy, and geographic distribution. Transactions of the Philosophical Society of New South Wales, 1, 1-38.

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