A FUTURE FOR THE STICK-NEST RAT
(Leporillus Conditor)

 

 by Annelise Wiebkin

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So what is so interesting about the Greater Stick-nest Rat?  This native herbivorous rodent is one of Australia’s most endangered animals.  Early explorers in Australia in the 1850s knew that the stick-nest rat roamed over southern Western Australia, South Australia and the lower Darling Basin in New South Wales.   Now they are only found naturally on two tiny islands off Ceduna S.A. - The Franklin Islands where between one and two thousand survive.    Reintroduction programs are being undertaken on Reesby and St Peter Islands to establish new colonies. Respectively, these islands are situated off the Tumby Bay coast and in the Neuyts Archipelago close to Ceduna.   I was involved in a week-long field trip to the latter, in September 1993, on which, release and survival data were monitored.   If these programs are successful, the rats will, hopefully, be released on the mainland within the dog fence on the Eyre peninsular.  

The Rats have been well known for their great nests of sticks and vegetation. The nests are built up to about a metre in height and a couple of metres in diameter. They are designed to protect the rat communities from harsh fluctuations in temperature and from predators such as dingos and sea eagles. Nest building is the alternative to compensate for the rats’ inability to dig burrows. These fabulous architectural constructions are often built around a bush with a maze of tunnels running throughout the nest.   The Stick-nest Rats have incredibly strong jaws for dragging branches to the nest-building site. Grass is also woven into the interior walls where between ten and twenty rats live.  

The Greater Stick-nest Rat is a very attractive rodent with a body similar to that of a rabbit.   The fluffy, fine, soft fur of the body and tail is usually grey brown with a white underside.   The head and body is about 220mm in length and the tail is a further 170mm.   Body weight varies considerably (180-450 gms).   The nose is quite blunt and, for a rodent, the eyes and ears are large.   The hind feet have distinct white markings on the upper surfaces.   The Stick-nest Rat’s diet consists of succulent ground vegetation such as Pig-face, Nitre Bush and Ice Plant.    These plants are digested by a succulate stomach and a very large caecum.    Breeding is constant throughout the year.    Gestation is about 6 weeks (the longest for an Australian rodent) with about 1-3 young being born.    The new-born attach themselves to the teats for a month, resulting in them being dragged around until they are weaned.    These amazing little creatures rarely attempt to bite when handled, although their benign nature may have made hunting easy for Aboriginals before European settlement. They have subsequently had to compete with sheep, cattle and rabbits for maintenance of their ecological niche. Cats and foxes have also been substantially responsible for their demise on the main land.    The Lesser Stick-nest Rat was a relative of the greater stick-nest Rat but is now, unfortunately, presumed extinct.   The Lesser Stick-nest Rat was a smaller version of its larger cousin but it had a longer tail, tipped with white.   Only a little history of this animal is known except that it lived along the Murray across South Australia and in southern Western Australia.    Early settlers tamed these animals as pets and also ate their tender white meat.    But like the Greater Stick-nest Rat, it was wiped out as a consequence of the intrusion of domestic animals such as sheep and cattle.    The last specimen was found in 1933 but an unconfirmed sighting was reported in 1970 from Western Australia.    

The program to establish a colony of Stick-nest Rats on St Peter Island has been under way for about 8 months.    St Peter Island is several kilometers from The Franklin Islands and is the largest in the region - about 40Km2 - with vegetation similar to that of The Franklins.    In September I was fortunate enough to join the field trip to the Island to assist Robert Brandle monitor rat survival.    Several trips had been made over the previous five months, which represented the duration of the initial introductions of animals to the island.    As with the previous trips, we stopped on our way to Ceduna, at Monarto Zoo to pick up 18 more Stick- nest Rats which were part of a controlled breeding program.   Amongst these animals, five were fitted with radio transmitter collars in a similar way to many of the previously released animals.   About 66 rats had been released over that initial five month period.   Approximately 69 rats could be accounted for on the island after births and deaths had been determined.   On arrival at Ceduna, we took a boat to the island and released eight of our consignment of rats on the northern coast (designated Site A) and 10 on the southern coast (Site B). Pitfall and Elliot traps were set up where we found tracks in the sand.   We also started tracking radio-collared rats which had been released on previous trips as well as those that had just been released.   The low bushland has limestone cliffs with many caves. The land is still recovering from intensive and prolonged sheep grazing which ceased over 30 years ago following acquisition by the National Parks and Wildlife Service.   The predators on the island that now may threaten the stability of the Stick-nest Rats’ future are Black Tiger Snakes, White Breasted Eagles, Barn Owls and possibly Osprey.    While fossicking in caves for evidence of dead Stick-nest Rats, e.g. skulls in owl pellets, we discovered a female Barn Owl sitting on five eggs. Elsewhere a pair of Osprey was building a nest and we observed a pair of 2 month-old Sea Eagles on a nest.   The natural balance between these hazards and the Stick-nest Rats’ ability to survive will be monitored.    

The pitfall traps were quite successful but the Elliot traps only captured three Stick-nest Rats together with plenty of mice.   We replaced exhausted radio-collars and ear tagged a few of the new-born, two of which were still attached to teats.   Two dead rats were discovered after radio tracking and a few collars were located in the sand having been detached by some un-identified means. Average body weights dropped considerably over the first week of release, but recovered well by twelve weeks.    The weights became stable at about 330 grams.   The rats are beginning to spread and some have travelled the 10 km to the opposite coast in less than eight weeks.    There are actually no stick nests on the island as many of the dense bushes act as satisfactory nests in their own right. Moreover, on the southern coast there are many Mutton Bird burrows which have been temporarily occupied by the rats whilst the birds are away migrating.   This may be a problem to the rats’ survival as the young rats are very easy prey to the many snakes which are known to take the young birds in such burrows. 

The population of radio-collared rats appears to be gaining or maintaining good body weight, reproducing well and avoiding predation.   Assuming that they represent the whole population, the future for the Greater Stick-nest Rat looks promising.  

Update 2005 

The National Parks website states in part, that The Franklin Islands population remains stable at approximately 1,000 rats.    Three new populations, Salutation Island, St Peter Island and Reevesby Island, have been established, and two further mainland populations are in the process of being established (Roxby Downs (SA) and Heirisson Prong (WA)).     

Acknowledgements to Department of Heritage and Environment - for further information go to

 http://www.environment.sa.gov.au/biodiversity/sticknestrat.html

       Ed

 
 
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