The quokkas of Rottnest Island
The quokka is possibly the most well known animal on Rottnest Island. It was first observed by a European in 1658 when the Dutchman, Volkersen, wrote that it resembled an Asian civet cat, but with brown hair. In 1696 de Vlamingh described the quokka as "a kind of rat as big as a common cat". He named the Island 'Rotte nest' (meaning 'rat's nest') and the name of the Island was eventually adapted to 'Rottnest'.
A marsupial the size of a hare or domestic cat, the quokka is the sole representative of the genus Setonix. As with other marsupials, such as the kangaroo, wallaby, wallaroo, bettong and potoroo, the females suckle their young in a pouch. Quokkas congregate under dense shrubs for shelter, and are less active during the day. They give birth in late summer, after a gestation period of twenty-seven days, and the young quokka remains in the pouch until August or September, and is then suckled for a further two months. The quokka reaches maturity at about one-and-a-half to two years of age, and lives to be ten years old.
The quokka is extremely adaptable. At the western end of the Island, Cape Vlamingh, there is no fresh water in summer but the quokkas are able to survive by obtaining water from plant life, particularly succulent plants such as the Pigface. This marsupial is a herbivore, capable of stripping most species of small trees and shrubs of their leaves and bark. They also eat grasses and succulent plants.
When Europeans first settled in Western Australia the quokka was widespread in many parts of the south-west as well as on Rottnest, Bald Island and in the vicinity of Perth, probably as far north as Moore River. The name "quokka" comes from the name given to the animal by the Aboriginal people living in the Augusta and King George Sound area of the south-west of Western Australia.
It is believed about 10,000 quokkas inhabit Rottnest Island at a density of five animals per hectare, with the numbers ranging from 4,000 to 17,000, depending on the availability of food and water in any given year.
Problems such as anaemia and high mortality amongst the young are caused by decreased nitrogen content of plants in summer and insufficient water, both of which are necessary for the production of protein. Quokkas also face deficiencies in the important trace elements cobalt and copper, which are scarce in Rottnest Island soils. It appears that the copper level is a controlling element in how the animals breed.
It is important for visitors to refrain from feeding quokkas and other fauna on Rottnest Island. Quokkas may become very ill as a result of eating unsuitable food such as bread, chips and meat. Rottnest Island Rangers may issue infringements to people who feed quokkas