Nabarlek

Nabarleks have teeth like a shark, with new molars continuously emerging from the back!

The nabarlek, also known as the pygmy rock-wallaby or little rock-wallaby, is a tiny member of the Macropodidae family. It is a relative of kangaroos, wallabies, tree-kangaroos, quokkas, and several other marsupial species native to Australia. Nabarleks are an endangered species, native to only a couple of small areas in northwestern Australia. They are at risk due to fires, competition for food, and predation by a destructive introduced species, the feral cat. Nabarleks are incredibly secretive, spending most of their time hidden in caves and crevices on steep, rocky slopes. They come out mostly at night, and they forage on grasses, sedges and tough ferns. These ferns wear down their teeth quickly, but that’s okay, because they continually produce new molars, a lot like sharks!

Incredible Nabarlek Facts

• Nabarleks only grow to be a little over a foot long, not including their tail.
• One subspecies is known from only a single specimen collected nearly 200 years ago.
• Females can get pregnant again right after giving birth and put their new embryo on pause.
• Island subpopulations are more secure than those on the mainland, because there are no cats.
• Nabarleks can eat ferns that contain more than 25 percent silica.
• Aboriginal Australians have hunted nabarleks for food for generations.

Where to Find Nabarleks

Nabarleks are native to a couple of areas in the far northern part of Australia. One subspecies, P. concinna canescens, lives in the Arnhem Land region of the Northern Territory and in the Kakadu National Park. The subspecies, P. concinna monastria lives along the northwestern coast of the Kimberley region of Western Australia, including a handful of small offshore islands. It is unknown whether the third subspecies, P. concinna concinna, still exists, but it was once found in the Top End region of the Northern Territory.

The nabarlek lives on rocky terrain, primarily sandstone or granite. It sticks to areas with steep slopes like rocky hills, cliffs and gorges. It prefers areas with plenty of good places to hide, such as caves and crevices or large boulders. Nabarleks live on the mainland of Australia as well as a few small, rocky islands not far from the shore. They do forage a considerable distance away from the safety of their rocky homes, in grassy areas or among sedges.

Nabarlek Scientific Name

The common name “nabarlek” is an Australian Aboriginal word that comes from the Kunwinjku dialect of the Bininj Kunwok language. The nabarlek is also known as the pygmy rock-wallaby or the little rock-wallaby. Its scientific name is Petrogale concinna. The genus, Petrogale, was established in 1837 by esteemed British zoologist John Edward Gray. It contains the rock wallabies. The specific name, concinna, is a Latin term meaning pretty.  

The original named subspecies, P. concinna concinna, is known only from a single specimen that was collected in 1839 and described by John Gould in 1842. Two additional subspecies, P. concinna canescens and P. concinna monastria were identified later.

Nabarlek Appearance

Nabarleks are tiny marsupials from the Macropodidae family, which includes kangaroos, wallabies, tree-kangaroos, quokkas and several other species. They are one of the smallest species of rock-wallabies. Nabarleks grow to a length of 12.2 to 14.4 inches, not including their long tails. They weigh a mere 2.65 to 3.53 pounds.

Depending on the subspecies, nabarleks may be a little darker or lighter in color. They have soft, light gray fur with a marbled appearance and black markings. Their back is tinged red. Their fur is short and silky over most of their body, except the tip of the tail. There the black fur grows longer, giving it a bushy appearance. Nabarleks hold their tails high, arched up and over their bodies, when they jump.

Nabarleks have large hind feet that they use together on land and separately in the water. The thick soles of the nabarlek’s feet are granulated. This helps it to grip the rocky surfaces where it spends most of its life.  

The nabarlek is difficult to distinguish from similar species in the field. It is most closely related to two other tiny rock-wallabies: the short-eared rock-wallaby, Petrogale brachyotis, and the monjon, Petrogale burbidgei.

Nabarlek Behavior

If there was just one word to describe the behavior of nabarleks, it would be secretive. These little marsupials are mostly nocturnal, and they spend much of their time hiding among rocks. They avoid traps and listen carefully for approaching danger. Juveniles are rarely seen.

Although nabarleks are generally nocturnal, they spend more time outside during the day in the rainy season. At that time, they can be found foraging in the morning and at dusk, and outside their caves even in the middle of the day.

Individuals are most at risk when they venture away from the safety of the rocks to forage. They sometimes wander hundreds of meters away from the rocky hillsides in search of grasses and sedges. When they go out into the open, grassy areas they are easy prey for feral cats.

Diet

The nabarlek is an herbivore. It eats grasses and sedges, and according to indigenous people from the area, it also eats fruits and digs for yams. Nabarleks also eat a lot of ferns. Few animals are able to eat the tough and abrasive fronds of ferns, but nabarleks have an advantage. They are one of only five known mammalian species that have continuously emerging teeth, much like a shark.

Throughout a nabarlek’s life, it keeps producing new molars which emerge from the back of its mouth. As its old teeth are worn down from chewing tough ferns, the new molars push forward. They are termed, “marching molars,” because new teeth, up to 80 in each row, just keep marching forward as the old ones wear away.

Nabarlek Reproduction

Male nabarleks reach maturity by two years of age, with females maturing by around 14 months. Pairs produce one offspring at a time, called a joey. Gestation lasts 30 days, after which the joey stays in its mother’s pouch for about 160 days.

Female nabarleks can be extremely aggressive. In captivity they have mauled and even killed males after mating. Females also wean their young quickly and aggressively, in the span of about two weeks. Other rock-wallabies typically allow their young to stay close for three to six months after leaving the pouch.

Nabarleks can breed year-round. Females undergo a postpartum estrous period, meaning they are fertile right after giving birth. If impregnated at that time, they can essentially pause the growth of their next embryo until the current joey leaves the pouch. As soon as it is removed, gestation resumes, and the female gives birth to a new joey within about two weeks. She will sometimes have overlapping offspring at the breast, one in the pouch and the other at foot, before the older joey is fully independent.  

Predators & Threats

Feral cats, an introduced species in Australia, are the main predators of nabarleks. Pythons and eagles are also known predators of these small mammals. Predators such as foxes and dingoes do not live in the areas that the nabarlek inhabits, so they are not a threat to the species at this time.

The indigenous Bininj people also hunt nabarleks, traditionally with spears but more recently with firearms. They report sometimes using fire to flush the animals out during a hunt.

Fire is a serious threat to nabarleks. As fires have increased in number and intensity, the nabarlek populations have declined. This may be due in large part to the destruction of nearby food sources.

Another threat to the nabarlek comes in the form of competition for food sources and habitat degradation by grazing animals such as cattle. As food becomes more scarce, the nabarlek has to venture farther and farther from safety.

Lifespan of the Nabarlek

Nabarleks live around 11.7 years on average, but some have reached the age of 17. The IUCN Red List of Threatened Species lists the nabarlek as an endangered species. The most recent assessment, done in 2014, estimated the nabarlek population between 5,000 and 10,000 mature individuals. Although hard data on the elusive species is scarce, the population is thought to be rapidly declining. Only the island subpopulations are believed to be secure at this time. Keeping the nabarlek safe depends largely on preventing the introduction of feral cats to those environments.  

Similar Animals

1. Kangaroo – This large marsupial can jump more than 30 feet in a single bound.
2. Tree Kangaroo – This member of the Macropodidae family is the only type that lives in trees.
3. Quokka – Short, round, and always ready with a smile, this member of the Macropodidae family is a social media star.

1. Sue Churchill, Available here: https://www.researchgate.net/publication/323644049
2. Wendy R. Telfer and Murray J. Garde, Available here: https://www.jstor.org/stable/27654126
3. Alison Ballance, Available here: https://www.rnz.co.nz/national/programmes/ourchangingworld/audio/2018642025/wallaby-vs-shark-a-toothy-quirk-of-nature
4. Stephanie Todd, Available here: https://library.dbca.wa.gov.au/static/FullTextFiles/926546.pdf
5. IUCN Red List, Available here: https://www.iucnredlist.org/species/16761/21955087#assessment-information