Biology of bilbies

Bilbies at a glance

Bilbies are well adapted for survival in the semi-arid and arid areas of Australia but they are under threat. They are listed as vulnerable nationally and endangered in Queensland.

The Greater Bilby is a solitary, nocturnal, omnivorous marsupial.

Remaining wild population occupies three major habitat types:

  • open tussock grasslands on uplands and hills
  • mulga woodland / shrubland on ridges and rises
  • hummock grasslands in plains and alluvial areas.

Bilbies are fossorial and may have many burrows within an occupied home range.

Bilby home ranges shift with food availability and are highly variable in size, examples recorded include 20–50ha (south-west Queensland) and 110–300ha (Northern Territory). ‘Burrow ranges’ are considerably smaller than home ranges.

Males are generally larger (800–2500g) and heavier than females (600–1100g).

Females can be reproductively active at 5 months, males at 8 months.

Litters number 1–3 offspring (usually 2).

Generation time is about 4 years.

Longevity in wild and captivity is up to 11 years.

Key threats:

  • predation (by foxes, cats, dingoes)
  • habitat (cover) loss through very large fires
  • grazing by rabbits/livestock (actual extent of threat unclear)

Dingo predation of feral cats has been recorded and is thought to be important in limiting cat densities where dingoes occur. This suggests that precautions are necessary when planning fox/cat control techniques.

Adapted from Copley, P. (2015) Proceedings of the Greater Bilby Recovery Summit.

Distribution and habitat

Bilbies live in spinifex grasslands and mulga scrublands in the hot, dry, arid and semi-arid areas of Australia. Previously more widespread, the bilby is now only found in remote parts of western Queensland, the Northern Territory and Western Australia.

They live in spiralling burrows which they dig up to 2m deep. This depth helps to keep them safe from predators and also to keep them at a constant temperature of 23°C, as bilbies can become heat stressed. A bilby may have as many as 12 burrows, one for sleeping and the others for escaping from predators.

Description and behaviour

Australia once had two species of bilby – the greater bilby (Macrotis lagotis) and the lesser bilby (Macrotis leucura) — the lesser bilby is now extinct.

The greater bilby (also known as the ‘rabbit eared bandicoot’) is the largest member of the bandicoot family. This marsupial (pouched animal) measures up to 55cm in body length with a tail of up to 29cm long. Adult males weigh up to 2.5kg and the females average about 1.5kg.

Its coat is silky light grey and white and it has a long black and white crested tail with a naked spur-like tip.

Bilbies have a long pink snout which is hairless at the tip. They have about 28 teeth, a long sticky tongue and a well-developed sense of smell to aid in finding food.

Their large, hairless ears are extremely useful for listening for predators as well as prey. These long ears allow a portion of them to remain above ground level when they are digging so they can hear predators approaching. Their eyesight is very poor and they are also sensitive to light.

They have strong forearms and hind legs for digging burrows and manipulating food.

The greater bilby is nocturnal. They don’t emerge from their burrows until an hour after dusk and retreat at least an hour before dawn. A full moon, strong wind, and heavy rain can keep a bilby in its burrow all night.

Diet

The bilby is omnivorous and its diet includes bulbs, fruit, seeds, fungi, insects, worms, termites, small lizards and spiders. One of its favourite plant foods is the bush onion or yalka which grows in desert sand plains after fires.

Bilbies don’t need to drink water regularly because, like the koala, they get most of their moisture from their food.

Breeding and life history

The female bilbies only associate with males to mate. This is a fast-breeding species with pregnancy lasting only 12 to 14 days.

When the baby joey is born it looks like a baked bean with legs. It stays in its mother’s pouch for between 75 and 80 days and is independent about two weeks later. Female bilbies have a backward-opening pouch with eight nipples. The pouch opens backward so as not to be filled with earth while digging.

Bilby-birth.jpg

At six months the female bilby can breed and usually has one or two young at a time. Although it is rare, she can have triplets. In a good season in the wild, bilbies can have up to four litters.

They can live for 6 to 7 years in the wild and 11 years in captivity.

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