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DISPLAYING POSTS TAGGED: fieldwork (2)

Desert rains trigger rat plagues

Author
by Karen Rowe
Publish date
3 August 2011
Comments
Comments (3)

Karen Rowe is a Research Associate at MV where she studies evolutionary ecology and behaviour in birds and mammals.

Record levels of rainfall in the Northern Territory have brought forth one of Australia’s rare and unique native mammals, the Long-haired, or Plague Rat (Rattus villosissimus). These herbivorous rats feed largely on stems and leaves and, with consistently high rainfall, large areas of the desert landscape have become lush with food. Coupled with an unusually high reproductive rate, where a single female can produce more than 200 young in one year, these rats are capable of large-scale population explosions leading to rapid dispersal over huge distances. They have even been documented moving as much as 3 km in a single night.

In the past, these rodents have spread across the arid regions of Australia, including eastern Western Australia, the Northern Territory, eastern Queensland and parts of South Australia. Historic plagues have been documented as far back as 1847, with others occurring in 1916-18, 1930-32, 1940-42, 1948, 1950-52, 1956, and 1966-69.

Once the plague recedes, they vanish almost as quickly as they arrived and during non-plague years, they become rare and hard to find, persisting in only a few locations.

Taking advantage of this unique opportunity to document the latest plague, I joined MV mammal curator, Kevin Rowe, and collections manager, Wayne Longmore, to try to find these rats in the Northern Territory, along the Finke River.

Kevin Rowe and Wayne Longmore MV curator, Kevin Rowe (left), and collections manager, Wayne Longmore (right), trapping rats in the desert rain.
Image: Karen Rowe
Source: Karen Rowe
 

We found them in abundance – nearly all of our live traps contained a long-haired rat, and one had two!

Rattus villosissimus caught along the Finke River Rattus villosissimus caught along the Finke River.
Image: Karen Rowe
Source: Karen Rowe
 

We even found part of the skeleton of one in a bird pellet – the undigested material regurgitated by a bird, particularly in birds of prey.

Bird pellet before dissection Bird pellet before dissection.
Image: Karen Rowe
Source: Karen Rowe
 

Bird pellet after dissection After dissection – most of the skull and jaw were intact (on left).
Image: Karen Rowe
Source: Karen Rowe
 

Long-haired rats build burrows in the sand, consisting of meters of tunnels with multiple entrances and exits. They use these burrows extensively, spending nearly 80% of their time underground.

Rattus villosissimus burrow entrance Rattus villosissimus burrow entrance.
Image: Karen Rowe
Source: Karen Rowe
 

At the Finke River site, the sandy soil made it easy to see footprints into and out of these burrows.

Rattus villosissimus footprints Rattus villosissimus footprints.
Image: Karen Rowe
Source: Karen Rowe
 

Kevin and Wayne are still on the hunt for the plague rat, hoping to find more populations in the Barkly Tablelands and central NT. By studying these rats from throughout the state and recording natural history data such as behaviour and habitat, as well as traits of the rats themselves, including age and reproductive state, we can better understand the ecology and biology of this unique, native, and (most of the time!) rare mammal.

Links:

MV Blog: On rats

Scientists with suction

Author
by Blair
Publish date
1 May 2011
Comments
Comments (1)

I recently accompanied Richard Marchant to the Shoalhaven River where he studies the animals that platypus eat. Thanks to the suction sampling tool we used, I'll never look at a common household vacuum cleaner the same way again.

The underwater vacuum we used is a quite different to that used to clean carpets: suction, in this case, created by bubbles are injected near the base of a pipe. The bubbles rise to the top, sucking water upward as they go.

Diving for platypus prey Richard Marchant diving with the air-lift sampler, which works like an aquatic vacuum cleaner.
Image: Julian Finn
Source: Museum Victoria
 

When placed over a river bed or sea floor, small animals and sand are also sucked up with the water. A mesh bag covering the top of the pipe acts like a sieve; the sand passes out but the animals remain trapped.

This method of suction sampling typically nets catches of crustaceans, insects, and insect nymphs – important food chain species that can be identified and counted for research.

Richard emptying air-lift sampler Emptying the mesh bag of the air-lift sampler.
Source: Museum Victoria
 

The machine sounds weird too: a dull rumble through a dive hood, perhaps a cross between a V8 car engine and thunder.

The air-sucking principle of the vacuum means people refer to it as an 'air-lift'. It’s a nifty invention and a system used by many aquatic biologists at one time or another in their career.

Links:

MV News: Linking the food chain

Video: Studying the diet of platypus

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Updates on what's happening at Melbourne Museum, the Immigration Museum, Scienceworks, the Royal Exhibition Building, and beyond.

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