The quokka, also known as the short-tailed scrub wallaby (//) (Setonix brachyurus), the only member of the genus Setonix, is a small macropod about the size of a domestic cat. Like other marsupials in the macropod family (such as kangaroos and wallabies), the quokka is herbivorous and mainly nocturnal.
Quokkas are found on some smaller islands off the coast of Western Australia, particularly Rottnest Island, just off Perth, and also Bald Island near Albany, and in isolated, scattered populations in forest and coastal heath between Perth and Albany. A small colony exists at the eastern limit of their range in a protected area of Two Peoples Bay Nature Reserve, where they co-exist with the critically endangered Gilbert's potoroo.
A quokka weighs 2.5 to 5.0 kg (5.5 to 11.0 lb) and is 40 to 54 cm (16 to 21 in) long with a 25-to-30 cm-long (9.8-to-11.8 in) tail, which is quite short for a macropod. It has a stocky build, well developed hind legs, rounded ears, and a short, broad head. Its musculoskeletal system was originally adapted for terrestrial bipedal saltation, but over its evolution, its system has been built for arboreal locomotion. Although looking rather like a very small kangaroo, it can climb small trees and shrubs up to 1.5 metres (4 ft 11 in). Its coarse fur is a grizzled brown colour, fading to buff underneath. The quokka is known to live for an average of 10 years. Quokkas are nocturnal animals; they sleep during the day in Acanthocarpus preissii, using the plants' spikes for protection and hiding.
Quokkas have a promiscuous mating system. After a month of gestation, females give birth to a single baby called a joey. Females can give birth twice a year and produce about 17 joeys during their lifespan. The joey lives in its mother's pouch for six months. Once it leaves the pouch, the joey relies on its mother for milk for two more months and is fully weaned around eight months after birth. Females sexually mature after roughly 18 months. When a female quokka with a joey in her pouch is pursued by a predator, she may drop her baby onto the ground; the joey produces noises, which may serve to attract the predator's attention, while the mother escapes.
Dutch mariner Samuel Volckertzoon wrote of sighting "a wild cat" on Rottnest Island in 1658. In 1696, Willem de Vlamingh mistook them for giant rats and named the island 't Eylandt 't Rottenest, from the 17th century Dutch meaning "rat nest".
In the wild, its roaming is restricted to a very small range in the South West of Western Australia, with a number of small scattered populations. One large population exists on Rottnest Island and a smaller population is on Bald Island near Albany. The islands are free of certain predators such as red foxes and cats. On Rottnest, quokkas are common and occupy a variety of habitats, ranging from semiarid scrub to cultivated gardens. Prickly Acanthocarpus plants, which are unaccommodating for humans and other relatively large animals to walk through, provide their favorite daytime shelter for sleeping. Additionally, they are known for their ability to climb trees.
Like most macropods, quokkas eat many types of vegetation, including grasses, sedges and leaves. A study found that Guichenotia ledifolia, a small shrub species of the family Malvaceae, is one of the quokka's favoured foods. Rottnest Island visitors are urged to never feed quokkas, in part because eating "human food" can cause dehydration and malnourishment, both of which are detrimental to the quokka's health. Despite the relative lack of fresh water on Rottnest Island, quokkas do have high water requirements, which they satisfy mostly through eating vegetation. On the mainland, quokkas only live in areas that have 600 mm (24 in) or more of rain per year. The quokkas chew their cud, similar to cows.
At the time of colonial settlement, the quokka was widespread and abundant, with its distribution encompassing an area of about 41,200 km2 (15,900 sq mi) of the South West of Western Australia, including the two offshore islands, Bald and Rottnest. By 1992, following extensive population declines in the 20th century, the quokka's distribution on the mainland had been reduced by more than 50% to an area of about 17,800 km2 (6,900 sq mi).
Despite being numerous on the small, offshore islands, the quokka is classified as vulnerable. On the mainland, where it is threatened by introduced predatory species such as red foxes, cats, and dogs, it requires dense ground cover for refuge. Clearfell logging, agricultural development, and housing expansion have reduced their habitat, contributing to the decline of the species, as has the clearing and burning of the remaining swamplands. Moreover, quokkas usually have a litter size of one and successfully rear one young each year. Although they are constantly mating, usually one day after the young are born, the small litter size, along with the restricted space and threatening predators, contributes to the scarcity of the species on the mainland.
An estimated 4,000 quokkas live on the mainland, with nearly all mainland populations being groups of fewer than 50, although one declining group of over 700 occurs in the southern forest between Nannup and Denmark. In 2015, an extensive bushfire near Northcliffe nearly eradicated one of the local mainland populations, with an estimated 90% of the 500 quokkas dying.
In 2007, the quokka population on Rottnest Island was estimated at between 8,000 and 12,000. Snakes are the quokka's only predator on the island. The population on smaller Bald Island, where the quokka has no predators, is 600–1,000. At the end of summer and into autumn, a seasonal decline of quokkas occurs on Rottnest Island, where loss of vegetation and reduction of available surface water can lead to starvation.
This species saw the most significant decline from 1930 to the 1990s, when their distribution was reduced by over half (de Tores et al., 2007). The quokka markedly declined in its abundance and distribution in the early 1930s, and this tendency has continued till today. Their presence on the mainland has declined to such an extent that they are only found in small groups in bushland surrounding Perth. The quokka is now listed as vulnerable in accordance with the IUCN criteria.
Quokkas have little fear of humans and commonly approach people closely, particularly on Rottnest Island, where they are abundant. Though quokkas are approachable, there are a few dozen cases annually of quokkas biting people, especially children. There are restrictions regarding feeding. It is illegal for members of the public to handle the animals in any way, and feeding, particularly of "human food", is especially discouraged, as they can easily get sick. An infringement notice carrying a A$300 fine can be issued by the Rottnest Island Authority for such an offence. The maximum penalty for animal cruelty is a A$50,000 fine and a five-year prison sentence.
Quokkas can also be observed at several zoos and wildlife parks around Australia, including the Perth Zoo, the Taronga Zoo, Wild Life Sydney, and the Adelaide Zoo. Physical interaction is generally not permitted without explicit permission from supervising staff.
Quokka behavior in response to human interaction has been examined in zoo environments. One brief study indicated fewer animals remained visible from the visitor paths when the enclosure was an open or walk-through environment. This may have been due to the quokkas acquiring avoidance behavior of visitors, which the authors propose has implications for stress management in their exhibition to the public.
In the mid-2010s, quokkas earned a reputation on the internet as "the world's happiest animals" and symbols of positivity due to their beaming smiles. Many photos of smiling quokkas have since gone viral, and the "quokka selfie" has become a popular social media trend, with celebrities such as Chris Hemsworth, Shawn Mendes, Margot Robbie and Roger Federer participating. Tourist numbers to Rottnest Island have subsequently increased.
Noting the popularity of smiling quokkas, the fact-checking website Snopes confirmed in 2020 that the animal exists, saying it had received questions from readers who thought it "was simply too cute to be real".