Bilby

Bilby (Macrotis lagotus)

PHYSIOLOGY | IMAGES | ETYMOLOGY | TAXONOMY | GEOGRAPHY | BEHAVIOR | DIET | REPRODUCTION | ECOLOGY | CONSERVATION | FAUNAFACTS | VIDEO | SOURCES

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The bilby is a semi-fossorial marsupial endemic to northwest Australia. This opportunistic, nocturnal omnivore leaves its burrow as the sun sets to forage using its large ears to disperse body heat and locate termites digging underground. This marsupial has a short gestation because young is born premature and develops in the mother’s pouch.

Physiology

Bilbies share similar characteristics to bandicoots including a long muzzle and very large ears. Compared to bandicoots, bilbies have a longer tail, bigger ears, and softer, silkier fur.

The bilby’s fur is soft, silky, and blue-grey in color with a mix of tan or fawn over the majority of the body. The belly is covered in white or cream fur. The fur does not protect the bilby’s body well from termite bites.

The first part of the bilby’s tail is the same blue-grey as the body with the remainder of it being black and the final 40% being pure white with a distinct crest.

Bilbies are known for their large, relatively hairless, rabbit-like ears. The bilby also has a long, pointed snout with sensory vibrissae and a hairless pink nose. The snout contains a long, sticky, slender tongue that is used to lap up termites.

Bilby hindlimbs are slender and similar to those of kangaroos. Rather than hopping, bilbies use their legs to gallop around the desert. The bilby’s forelimbs are strong and consist of three clawed digits and two clawless digits.

Bilbies average about 29-55 centimeters in length, or 11-22 inches. Bilbies display sexual dimorphism as males have enlarged foreheads, longer canines, and a body mass that is twice that of females. At 800-2,500 grams (1.7 to 5.5 pounds), the male bilby is about the same size as a rabbit. Male bilbies in good condition have even been known to grow up to 3.7 kilograms (8.2 pounds) in captivity. The female is smaller, and weighs around 600 to 1,100 grams (1.3 to 2.4 pounds).

Female bilbies have a pouch that opens to the rear so as to avoid filling with soil when the animal is burrowing. They also have nipples both deep inside the pouch and nipples that hang outside the pouch. Each type of nipple provides a different type of milk for the offspring living outside the pouch versus inside the pouch.

The oldest bilby in captivity lived about 10 years, although six to seven years of age is a typical maximum lifespan in captivity. The lifespan of bilbies in the wild is unknown.

SEXUAL DIMORPHISM
Larger Males with Enlarged Foreheads and Longer Canines
BODY LENGTH
29-55 cm. / 11-22 in.
BODY MASS
600-2,500 g. / 21-88 oz.
DENTAL FORMULA
I ⁵⁄3, C ¹⁄1, P ³⁄3, M ⁴⁄₄, ×2 = 48
LIFESPAN
5-10 yr.
GENERATION LENGTH
4 yr.
LOCOMOTION
Digitigrade

Images

Taxonomy

Bilbies, once known as greater bilbies, are the only extant member of Thylacomyidae in the order Peramelemorphia after their closest relative, lesser bilbies (Macrotis leucura), became extinct in the 1930’s and 1960’s. The placement of bilbies within the Peramelemorphia order has changed in recent years. Vaughan (1978) and Groves and Flannery (1990) both placed this family within the family Peramelidae, but Kirsch et al. (1997) found them to be distinct from the species in Peroryctidae (which is now a subfamily in Peramelidae). McKenna and Bell (1997) also placed it in Peramelidae, but as the sister of Chaeropus in the subfamily Chaeropodinae.A scientific description of the bilby was first published in 1837 by Mr. J. Reid. Reid based his description on a specimen that he erroneously stated to have come from Van Diemen’s Land (now Tasmania), where the species has not occurred in historical times. As all bandicoot species were then placed in a broadly circumscribed Perameles, Reid placed the bilby there too. However, noticing how different it was from other members of the genus, he noted that if more species were discovered to be similar to the bilby, the characteristics would constitute a subgenus to which he suggested the name Macrotis.

The following year, Richard Owen proposed to the Zoological Society of London to erect a new genus for this species, Thylacomys. This name was widely adopted and remained in use for many years until B. Arthur Bensley erected a subfamily to hold the genus in 1903, Thylacomyinae. This name remains valid, and has since been promoted to family rank as Thylacomyidae. Thylacomys, itself, is no longer considered valid, as Reid’s original paper is held to have established the generic name Macrotis. Thus, the currently accepted scientific name for the bilby is Macrotis lagotis.

KINGDOM
Animalia
PHYLUM
Chordata
CLASS
Mammalia
ORDER
Peramelemorphia
FAMILY
Thylacomyidae
GENUS
Macrotis
SPECIES
Lagotis
SUBSPECIES
None

Etymology

The bilby was once known as the greater bilby, but is often referred to simply as the bilby since their closest relative, the lesser bilby (Macrotis leucura) became extinct in the 1930’s and 1960’s.

The term bilby is a loan word from the Yuwaalaraay Aboriginal language of northern New South Wales, meaning long-nosed rat.

The bilby is also known as dalgyte in Western Australia by the Noongar people. The Wiradjuri of New South Wales also call it bilby. Other vernacular names include pinkie and rabbit-eared bandicoot.

The bilby’s scientific name is Macrotis lagotis. The specific epithet lagotis was chosen from its resemblance to the rabbit, the lagomorph.

ALTERNATE
Dalgyte, Greater Bilby, Pinkie, Rabbit-Earted Bandicoot
YOUNG
Joey
Region

Bilbies were historically found over 70% of continental Australia with populations throughout South Australia, Western Australia, the Northern Territory, and New South Wales. Limited populations were also found in southwestern Queensland. Upon the introduction of feral cats (Felis catus), red foxes (Vulpes vulpes), and European rabbits (Oryctolagus cuniculus) by Europeans, the home range of the bilby was greatly reduced.

Today, bilbies are limited to 20 to 30% of their original territory and are found in Great Sandy, Tanami, and Gibson deserts in northwest Australia and the southwest tip of Queensland.

Bilbies are now considered extinct in South Australia.

EXTANT
Australia

Bilbies inhabit dry savanna and subtropical/tropical dry grassland habitats. They are commonly found in arid, hot areas including deserts, dunes, and grasslands.

There are three main vegetation types commonly associated with bilby habitat: tussock grassland commonly found on the hills and uplands, mulga woodlands and shrublands, and hummlock grasslands found on dunes and sandy plains.

SAVANNA
Dry
GRASSLAND
Subtropical/Tropical Dry

Co-Habitants

Behavior

Bilbies are terrestrial and semi-fossorial, found in areas consisting of rocky, clay soil. Unlike bandicoots, bilbies are excellent burrowers and can build extensive tunnel systems with their strong forelimbs and well-developed claws. Bilbies dig slightly spiraling burrows about 2 meters deep and up to 3 meters in length. These burrows may have multiple exits, which are particularly important if a burrow is invaded by a predator. A single bilby typically makes several burrows within its home range, up to about a dozen, and moves between them. These burrows serve as protection from predators as well as from the harsh sun and other environmental conditions and provide a safe place to cache young while adults are foraging.

Bilbies are nocturnal and leave their burrows as the sun sets to forage and search for mating opportunities. Bilbies may return to their burrow periodically throughout the night to rest or if threatened by a predator.

Bilbies have poor eyesight and mainly rely on hearing and olfaction for perceiving their environment. They have a keen sense of smell, which is used to sniff out food buried underground as well as perceive scent markings of other individuals. With their enormous ears, bilbies have excellent hearing. The ears of bilbies are also used to help regulate body temperature. By placing their enormous ears against the ground, bilbies are able to hear termites and other insects burrowing underground and can listen for predators. They then use their sharp claws and strong forelimbs to dig up insects, bulbs, and other buried food. Hearing seems much less important for bilbies than olfaction, however.

Bilbies tend to live solitary lives, though some may live together in pairs, usually two females.

Home range sizes of male bilbies are usually much larger than those of females. Female home ranges are from 0.18 to 1.5 square kilometers while males have home ranges of between 1.5 to 3.16 square kilometers. Home ranges of males, females, and juveniles are likely to overlap, but not much social contact is made with the exception of mating.

Captive male bilbies seem to possess a linear social hierarchy. Unlike bandicoots, this hierarchy is not maintained by high levels of aggression. Scent markings outside of burrows seem to signal where an animal is in the dominance hierarchy.

Communication between male bilbies usually occurs through scent markings. Males mark the outside of their burrows and the burrows where they have mated with a female by rubbing their urogenital area along the burrow entrance. This is thought to ward off lower-ranked males. Scent marking seems directly correlated to dominance. Dominant males mark over areas less dominant males have previously marked and less dominant males tend to avoid entering burrows of dominant males. Scent marks by males have little effect on females since males are rarely, if ever, aggressive towards females. Females rarely scent mark their territories.

CIRCADIAN RHYTHM
Nocturnal
MOVEMENT PATTERN
Non-Migrant

Diet

Bilbies have an opportunistic, omnivorous diet consisting of seeds, especially those of the grasses Dactyloctenium radulans and Yakirra australiense, bulbs, larvae, termites, ants, spiders, fruit, fungi, lizards, and occasionally eggs, snails, or small mammals.

The proportion of insect to plant material that makes up a bilby’s diet depends on the habitat and the season.

Bilbies do not drink water, but instead obtain water from their food.

Since bilbies have soft fur that does not protect their bodies well from termite bites, they dig tunnels leading to termite chambers and lap them up with their long, slender tongues. Unfortunately, this method of feeding leads to a large consumption of soil and sand as well.

Controlled fires are actually important to bilbies because fire promotes growth and seed production of preferred food plants.

PREFERENCE
Generalist
STYLE
Forager

Reproduction

Bilbies have a polygynous mating system in which the most dominant male will mate with the most dominant female and additional females while lower males will mate with females equal or below them in the social hierarchy.

Female bilbies reach sexual maturity at around five months old, or 560 grams, while males take around eight months, or at a weight of 800 grams, to reach maturity.

Bilbies have the ability to breed throughout the year, depending on environmental conditions. In their arid environments, females may delay mating until conditions are appropriate to support the nutritional demands of lactation and independence of the young.

Male bilbies initiate sexual interactions by approaching and following a female. This is followed by the male sniffing the female around her face, shoulders, flanks, or under the tail as well as licking the female’s urogenital opening. Females may also sniff the male. Females may aggressively rebuff the advances of lower-ranked males. Copulation seems to take place underground with the longest mating sessions recorded taking place for around 18 hours.

There is no evidence of pair bonding, though males will often scent mark the burrow after mating with a female. This is thought to ward off lower-ranked males.

These results were observed in a study of captive bilbies. Little has been recorded about bilby mating in the wild due to their decreasing numbers and semi-fossorial, nocturnal lifestyle.

The female bilby oestrus cycle lasts around 21 days. Bilbies have one of the shortest gestation periods of all mammals, only 14 days. When environmental conditions are favorable, a female bilby may produce up to four litters a year, each typically consisting of one to two offspring, though up to four offspring have been reported.

Female bilbies are the only caregivers of young and have a pouch that opens to the rear so as to avoid filling with soil when the animal is burrowing. While in the pouch, bilby offspring obtain all of their nourishment from the mother’s milk. Bilby females have nipples both deep inside the pouch and nipples that hang outside the pouch. Each type of nipple provides a different type of milk for the offspring living outside the pouch versus inside the pouch.

After their short, 14-day gestation, tiny, premature bilby offspring climb into their mother’s pouch and attach to a nipple where they remain for the majority of their time with their mother. During the 75 days the young bilbies remain in the pouch, the babies continue to grow at a very fast rate, reaching 200 grams by the time they leave the pouch.

Once the young emerge from their mothers pouch, they do not return. Many times, the female has already mated and a new neonate enters the pouch soon after the previous litter has left. These young juveniles are cached by the mother in one of her burrows where she returns regularly over the next two weeks to allow her babies to suckle and provide additional care.

After 14 days, the young leave the burrow and must fend for themselves with no additional parental care. It is estimated that only 25% of offspring produced will reach adulthood while the rest will become prey for predators or succumb to the elements.

BREEDING SEASON
Year-Round
BREEDING INTERVAL
3 Months
ESTROUS CYCLE
21 Days
COPULATION
18 Hours
PARENTAL INVESTMENT
Maternal
GESTATION
14-17 Days
POUCH LIFE
75 Days
LITTER
1-4
WEANING
75 Days
INDEPENDENCE
89 Days
SEXUAL MATURITY
5-8 Months


While native species, such as carpet pythons (Morelia spilota), monitor lizards (Varanidae), and some raptors (Accipitridae) are potential predators of bilbies, the most common and destructive predators are introduced species.

Non-native species that prey on bilbies include dingos (Canis lupus dingo), red foxes (Vulpes vulpes), and feral cats (Felis catus). Dingos were thought to have been introduced in Australia about 3,500 years ago. Red foxes were brought to Australia for the purpose of recreational hunting in 1855 by European settlers. Within 100 years of their introduction, red foxes spread across continental Australia and currently inhabits all regions of the continent with the exception of the tropical northern region of Australia. Domestic cats were originally released throughout Australia around 1855 to control the population of another invasive species, European rabbits (Oryctolagus cuniculus), as well as mice and rat populations. Domestic cats quickly expanded over the entire continent of Australia, killing many native species.

Bilbies were also once a favorite traditional food and source of fur for Aboriginal peoples of Australia.

While they are a source of food for a number of predators, both native and introduced, the most important role played by the bilby is that of an ecosystem engineer. Ecosystem engineers are organisms that modify, maintain, create, or destroy structure within the physical environment. As bilbies forage for bulbs, seeds, and insects, they dig pits up to 25 centimeters deep that are then abandoned. These pits become areas where seeds, water, and other organic matter settle and begin to decompose. Bilby pits become fertile patchesin the Australian desert where some seeds are provided the extra fertilization to germinate in an otherwise extremely difficult environment. Studies compared environments without bilbies and a similar, native fossorial group, bettongs (Bettongia), to those where these two native species are present. It was concluded that environments without these native, fossorial animals suffered from devastating losses of native Australian fauna despite the presence of rabbits, which also dig burrows.

Predators

Conservation

The bilby is evaluated as Vulnerable on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species because, although it still has a large extent of occurrence (EOO), it is patchily distributed and has a small area of occupancy (AOO), the population size is estimated to be fewer than 10,000 mature individuals, and it suffers from an ongoing decline estimated to exceed 10% over the last 3 generations of 12 years that is likely to continue.

Additionally, a taxon may be moved from a category of higher threat to a category of lower threat if none of the criteria of the higher category has been met for five years or more and even if the growth in numbers in translocated subpopulations offsets the decline in the wild, this has not been the case for more than five years for the bilby.

Bilbies are listed as Endangered under the U.S. Endangered Species List, and are on Appendix I of CITES. In Australian territories, bilbies are extinct in Queensland, threatened in the Northern Territory, vulnerable in Western Australia, endangered in South Australia, and presumed extinct in New South Wales.

Population

Like the lesser bilby, bilbies, also known as greater bilbies, have suffered a significant drop in population over the past 200 years.

Five translocations, one to an island and four to mainland islands, while providing valuable insurance against extinction, may not yet fully offset the continuing decline in the wild.

MATURE INDIVIDUALS
9,000
FRAGMENTATION
Not Fragmented
THREATS

Bilbies are threatened by the introduction of invasive predators such as dingos (Canis lupus dingo), red foxes (Vulpes vulpes), and feral cats (Felis catus), and invasive herbivores such as European rabbits (Oryctolagus cuniculus). The introduction of both European rabbits and livestock has greatly reduced the abundance of grasses, seeds, and other plant matter typically fed upon by native bilbies. As well as the reduction of plants through feeding, grazing has also led to the degradation of bilby habitat. Bilby habitat is also being destroyed as a result of human development and they are hit by cars along roads.

Along with the introduction of invasive species, a number of new diseases have also been brought to Australia. Bilbies are highly susceptible to the parasites and diseases of introduced animals and are commonly infected when they come into contact with feces of introduced species while digging. Without immunities to fight these parasites and diseases, many die as a result.

AGRICULTURE & AQUACULTURE
Livestock Farming & Ranching
INVASIVE & OTHER PROBLEMATIC SPECIES, GENES, & DISEASES
Invasive Non-Native/Alien Species/Diseases
ACTIONS

Bilbies are protected under Australian law and a number of breeding and reintroduction projects are underway, as well as projects to control populations of harmful invasive species.

Reintroduction programs of the bilby have begun in southern South Australia, southwestern Queensland, western New South Wales, and areas of Western Australia with some success due to the addition of predator-proof enclosures and intense monitoring of reintroduced populations.

Bilbies are promoted as a mascot for the Commonwealth of Australia Endangered Species Program.

Bilbies are also replacing rabbits as the Australian symbol of Easter, as chocolate bilbies are being sold as an alternative to chocolate bunnies. Since the 1990’s, bilby conservation groups have promoted the idea of replacing the Easter Bunny with the Easter Bilby. Chocolate shops around Australia began selling chocolate bilbies with a portion of the profit going to help fund bilby conservation.

Bilbies have their own Australian holiday, National Bilby Day, annually held on the second Sunday of September in hopes of raising funds and educating the public on bilby conservation.

FaunaFacts

Bilby

Bilby

Controlled fires are actually important to bilbies because fire promotes growth and seed production of preferred food plants.

Read more…
Bilby

Bilby

The lifespan of wild bilbies is unknown, but captive bilbies are known to live 6-7 years, the oldest living about 10 years.

Read more…
Bilby

Bilby

Bilbies are promoted as a mascot for the Commonwealth of Australia Endangered Species Program and are replacing rabbits as the Australian symbol of Easter.

Read more…

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