GILBERT'S POTOROO - AUSTRALIA'S MOST ENDANGERED MAMMAL
History of Gilbert's Potoroo - Discovery, Presumed Extinction and Rediscovery
Gilbert's Potoroo was discovered for science in 1840 by John Gilbert, an English naturalist and collector working in Western Australia for the zoologist John Gould. Gould named the new species Hypsiprymnus gilbertii and described it in the Proceedings of the Zoological Society of London published in 1841.
The first illustration of Gilbert's Potoroo (entitled "Gilbert's Rat Kangaroo") appeared in Gould's "Mammals of Australia". This was a limited edition folio sized publication produced for subscribers in three volumes. Each species was illustrated in a magnificent full-page hand-coloured lithograph. Gilbert's Potoroo appeared in volume 2, published in 1863, and the accompanying text quoted Gilbert's notes on the species. These notes survive in two slightly different versions, both in Gilbert's handwriting; the following copy contains all information found in the two versions.
This remained the only information about the habits of the species until its rediscovery in 1994.
John Gilbert collected the first specimens of Gilbert's Potoroo at King George Sound in 1840. The next European to find Gilbert's Potoroo was George Masters, who worked for the Museum of New South Wales (now the Australian Museum). He visited the Swan River Colony in 1866 and 1869 to obtain specimens for their collections, and collected seven Gilbert's Potoroos from somewhere between King George Sound and the Salt (Pallinup) River to the east of Albany, but he left scant information about his expeditions and no information about the potoroos.
Another collector, William Webb, obtained a single Gilbert's Potoroo, again from King George Sound, sometime between 1874 and 1879. This specimen is in the Macleay Museum at the University of Sydney.
This was the last official record of the species and by 1909 it was believed to be extinct (Shortridge, 1910).
In the late 1970's, a search was instigated in south-western Australia for Gilbert's Potoroo and the Broad-faced Potoroo. Tony Start and David Kabay made appeals to the public, followed leads and surveyed many areas along the south coast.
Tony and David were encouraged by a few old timers from the south coast who remembered 'miniature kangaroos'. These people sometimes saw them when hunting quokkas from horseback in the heathlands and occasionally caught them in rabbit traps. They knew the wildlife well and were emphatic that these were not bandicoots, although they were of a similar size. Nor were they quokkas, which they knew well.
Bearing in mind that Gilbert had noted the potoroo to be the 'constant companion' of the quokka, Tony and David sought and found many places on the south coast where quokkas still lived in swampy places, including Two Peoples Bay where, in September 1977, Tony set traps in Robinson's Gully. However, although they found many quokka colonies and caught quokkas at some locations, the survey did not turn up any evidence of survival of either potoroo species.
Quokkas eventually led to the rediscovery of Gilbert's Potoroo, although in a rather indirect way. In November 1994 Elizabeth Sinclair, a Ph.D. student studying population genetics of quokkas, and Bridget Hyder (a volunteer field assistant) were trying to catch quokkas to help with Elizabeth's research. They set 17 cage-traps at several locations in Two Peoples Bay Nature Reserve and these traps continued to be monitored by Elizabeth and Adrian Wayne.
By Tuesday 29th, the traps had been set for six nights without success. Then, the following morning, they found one of the traps occupied by an animal about the size of a bandicoot which, at first glance, resembled a baby quokka. The animal was female with a single pouch young. An ear-clip was taken and then the animal was released. The next morning, however, two more animals were captured; a juvenile male and a larger adult female, again with a single pouch young. Now there were small and large animals, looking the same as the animal captured on the previous morning, and it was decided that they were not, in fact, quokkas. Their fur was much too soft for them to be bandicoots and so they were taken back to the reserve research station for closer examination.
Elizabeth and Adrian conferred with Leigh Whisson and Alan Danks, CALM staff at the reserve, and by a process of elimination, using mammal identification books, the four of them began to realise that the animals fitted the description of Gilbert's Potoroo, last officially recorded in 1879!
Staff of the Western Australian Museum quickly gathered together relevant comparative material, including the skin of a Victorian Long-nosed Potoroo and skulls of Gilbert's and the Broad-faced Potoroos. Armed with the Museum specimens, a team of CALM scientists rushed from Perth to Two Peoples Bay to examine the mystery mammal. The animal's long, soft fur, roundish face and long, relatively thick, tail quickly distinguished it from the similarly-sized quenda (southern brown bandicoot). It did, indeed, look like a potoroo and examination of the distinctive teeth confirmed this. Since the skull shape of Gilbert's and the Broad-faced Potoroos is quite different, the length and width of the head was measured, finally confirming the first official record of Gilbert's Potoroo for 115 years.
After the excitement of making the discovery of a lifetime, Elizabeth Sinclair continued her study of quokkas, but incorporated an investigation of the potoroos. At that stage, Gilbert's Potoroo was considered to be the south-western subspecies of the Long-nosed Potoroo (Potorous tridactylus). However working with another geneticist, Mike Westerman, Elizabeth was able to show that Gilbert's Potoroo was as genetically different from the Long-nosed Potoroo as was the much larger Long-footed Potoroo. This exciting result justified treating Gilbert's Potoroo as a species in its own right, resurrecting Gould's original name Potorous gilbertii.
Gilbert's Potoroo was apparently locally abundant in the vicinity of King George Sound in the 19th century, as John Gilbert wrote in letters to John Gould (1863) that "immense numbers" could be captured by Aborigines in a single afternoon. Distribution does not appear to have been widespread, however, as Gilbert reported "I have not heard of this species being found in any other parts of the colony than King George's Sound". Also the specimens obtained by George Masters, in 1866 and 1869, together with the one individual taken by William Webb, sometime between 1874 and 1879, all came from the King George Sound region.
Only one modern specimen is known to have been taken outside the Albany area. It is an unsexed skull, collected outside Brides Cave near Margaret River. The collector and date are unknown, but the specimen, part of the Shortridge collection, is now held in the National Museum in Wales.
Sub-fossil specimens have been collected from cave deposits in the Margaret River area (for example Mammoth, Museum and Brides Caves) on the Leeuwin-Naturaliste ridge. Specimens from Devil's Lair have been dated to around 12,000 years ago. Specimens have also been found at Yanchep Caves. Apart from the specimen found near Brides Cave, which suggests that the species occurred recently on the Leeuwin-Naturaliste Ridge, there is no indication of its original distribution through the south west.
Despite continuing searches across south west Australia, the only known surviving population of Gilbert's Potoroo is the one rediscovered in 1994 on the slopes of Mount Gardner in Two Peoples Bay Nature Reserve, 35 kilometres east of Albany, on King George Sound.
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