Macrotis lagotis
greater bilby
(Also: bilby)

Greater 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 silvestris), red foxes (Vulpes vulpes), and rabbits Oryctolagus cuniculus by Europeans, the home range of Macrotis lagotis was greatly reduced. Today, bilbies are limited to 20 to 30% of their original territory. Macrotis lagotis is found in Great Sandy, Tanami, and Gibson deserts in northwest Australia and the south west tip of Queensland. Greater bilbies are now considered extinct in South Australia. Reintroduction programs 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. ("National Recovery Plan for the Greater Bilby Macrotis lagotis", 2006; Department of the Environment, Water, Heritage and the Arts, 2009; Northern Territory Government, 2006; Queensland Environmental Protection Agency, 2007)

Greater bilbies are commonly found in dry, hot areas including deserts, dunes, and grasslands. There are three main vegetation types commonly associated with bilby habitat. These are tussock grassland commonly found on the hills and uplands, mulga woodlands and shrublands, and hummlock grasslands found on dunes and sandy plains. Greater bilbies are fossorial, found in areas of rocky and clayey soil. ("National Recovery Plan for the Greater Bilby Macrotis lagotis", 2006; Department of the Environment, Water, Heritage and the Arts, 2009; Northern Territory Government, 2006; Queensland Environmental Protection Agency, 2007)

Greater bilbies are known for their large, relatively hairless, rabbit-like ears, and long pointed snouts with sensory vibrissae and a hairless pink nose. Their fur is soft, silky and bluish grey in color with a mix of fawn over the majority of the body. The belly is covered in white or cream fur. The first part of the tail is the same bluish grey as the body with the remainder of it being black and the final 40% being pure white. The pouch of females opens to the rear so as to avoid filling with soil when the animal is burrowing. The forelimbs are strong and consist of three clawed digits and two clawless digits. Greater bilby hind limbs are slender and similar to those of kangaroos. Rather than hopping, bilbies use their legs to gallop around the desert. Their tongues are long, sticky, and slender, making it easy to catch termites. Males and females are sexual dimorphic, with the male's body mass being twice that of females (800 to 2500 g for males relative to 600 to 1100 g for females). Along with being larger, males also have enlarged foreheads and longer canines (National Recovery Plan for the Greater Bilby). ("National Recovery Plan for the Greater Bilby Macrotis lagotis", 2006; Department of the Environment, Water, Heritage and the Arts, 2009; Northern Territory Government, 2006; Queensland Environmental Protection Agency, 2007)

Greater bilbies have a polygynous mating system in which the most dominant male will mate with the most dominate female and additional females while lower males will mate with females equal or below them in the social hierarchy. Males 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. (Johnson and Johnson, 1983)

Greater bilbies have the ability to breed throughout the year, whether breeding occurs depends 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. When environmental conditions are favorable, a female bilby may produce up to 4 litters a year, each typically consisting of 1 to 2 offspring, though up to 4 offspring have been reported. Female greater bilbies reach sexual maturity at around 5 months old (or 560 g) while males take around 8 months (or at a weight of 800 g) to reach maturity. The female oestrus cycle lasts around 21 days. Greater bilbies have one of the shortest gestation periods of all mammals, only 14 days. After gestation, the tiny, premature offspring climbs into its mother's pouch, attaches itself to a nipple and remains in the pouch for around 75 days. The young are cared for by the mother for an additional 14 days. After that, the young will leave their mother's burrow and be left to fend for themselves. ("National Recovery Plan for the Greater Bilby Macrotis lagotis", 2006; Humble, 2006; Johnson and Johnson, 1983)

Females are the only caregivers of young. After their short gestation, young greater bilbies climb into their mother’s pouch 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 g by the time they leave the pouch. While in the pouch, the offspring obtain all of their nourishment from 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. 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. After these two weeks, 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. ("National Recovery Plan for the Greater Bilby Macrotis lagotis", 2006; Humble, 2006; Queensland Environmental Protection Agency, 2007)

The oldest greater bilby in captivity lived about 10 years, although 6 to 7 years of age is a typical maximum lifespan in captivity. The lifespan of greater bilbies in the wild is unknown. ("National Recovery Plan for the Greater Bilby Macrotis lagotis", 2006; Friend, et al., 2008; Tydale-Bicsoe, 1973)

Greater bilbies tend to live solitary lives, though some may live together in pairs (usually two females). Greater bilbies are semi-fossorial, digging 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 may have several burrows scattered through its home range. These burrows serve as protection from predators as well as from the harsh sun and other environmental conditions. They also serve as a safe place to cache young while adults are foraging. As the sun sets, nocturnal greater bilbies leave their burrows to forage and search for mating opportunities. Greater bilbies may return to their burrow periodically throughout the night to rest or if threatened by a predator. Home ranges of males, females, and juveniles are likely to over lap, but not much social contact is made with the exception of mating. However, male greater bilbies in captivity 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. ("National Recovery Plan for the Greater Bilby Macrotis lagotis", 2006; Humble, 2006; Northern Territory Government, 2006)

Home range sizes of male greater bilbies are usually much larger than those of females. Female home ranges are from 0.18 to 1.5 square km while males have home ranges of between 1.5 to 3.16 square km. ("National Recovery Plan for the Greater Bilby Macrotis lagotis", 2006)

Greater 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, greater bilbies also listen for insects underground as well as predators. However, hearing seems much less important than olfaction. The ears of greater bilbies are also used to help regulate body temperature. Communication between males usually occurs through scent markings. Males mark the outside of their burrows by rubbing their urogenital area along the burrow entrance. Males may also mark burrows where they have mated with a female. Scent marking seems directly correlated to dominance; dominant males mark over areas less dominant males have previously marked. Also, less dominant males tend to avoid entering burrows of dominant males. Females rarely scent mark their territories. Scent marks by males have little effect on the females since males are rarely, if ever, aggressive towards females. ("National Recovery Plan for the Greater Bilby Macrotis lagotis", 2006; Humble, 2006; Johnson and Johnson, 1983; Northern Territory Government, 2006)

Greater bilbies do not drink water, they obtain water from their food. They have an opportunistic 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 their diet depends on the habitat and the season. Along with a keen sense of smell, greater bilbies have excellent hearing. Placing their enormous ears against the ground, greater bilbies are able to hear termites and other insects burrowing underground. They then use their sharp claws and strong forelimbs to dig up insects, bulbs, and other buried food. Since greater 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 greater bilbies because fire promotes growth and seed production of preferred food plants. ("National Recovery Plan for the Greater Bilby Macrotis lagotis", 2006; Department of the Environment, Water, Heritage and the Arts, 2009; Humble, 2006; Northern Territory Government, 2006; Queensland Environmental Protection Agency, 2007)

While native species such as carpet pythons (Morelia spilota), monitor lizards (Varanidae), and some raptors (Accipitridae) are potential predators of greater bilbies, the most common and destructive predators are introduced species. Non-native species that prey on greater bilbies include dingos (thought to have been introduced in Australia about 3500 years ago), red foxes, and feral cats. 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, as well as mice and rat populations. Domestic cats quickly expanded over the entire continent of Australia, killing many native species. ("National Recovery Plan for the Greater Bilby Macrotis lagotis", 2006; Department of the Environment, Water, Heritage and the Arts, 2009; Department of the Environment, Water, Heritage, and the Arts, 2004a; Department of the Environment, Water, Heritage, and the Arts, 2004b; Hintze, 2002; Northern Territory Government, 2006; Queensland Environmental Protection Agency, 2007; Tydale-Bicsoe, 1973)

While they are a source of food for a number of predators, both native and introduced, the most important role played by Macrotis lagotis is that of an “ecosystem engineer.” Ecosystem engineers are “organisms that modify, maintain, create or destroy structure within the physical environment” (Eldridge and James, 2007). As greater bilbies forage for bulbs, seeds, and insects, they dig pits up to 25 cm deep that are then abandoned. These pits become areas where seeds, water, and other organic matter settle and begin to decompose. Greater bilby pits become “fertile patches” in the Australian desert where some seeds are provided the extra fertilization to germinate in an otherwise extremely difficult environment. Studies compared environments without greater 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. (Eldridge and James, 2007)

Greater bilbies were once a favorite traditional food and source of fur for Aboriginal peoples of Australia. The rarity and protected status of greater bilbies means this practice has been all but abandoned. Greater bilbies are promoted as a mascot for the Commonwealth of Australia Endangered Species Program. They are also replacing rabbits as the Australian symbol of Easter, with chocolate bilbies are being sold as an alternative to chocolate bunnies. (Northern Territory Government, 2006; Queensland Environmental Protection Agency, 2007)

There are no known adverse effects of Macrotis lagotis on humans.

Greater bilbies are listed as Vulnerable on the IUCN red list, endangered under the U.S. Endangered Species List, and are on Appendix I of CITES. The conservation status in each of the Australian territories is as follows: Queensland - extinct, Northern Territory - threatened, Western Australia - vulnerable, South Australia - endangered, New South Wales - presumed extinct. Greater bilbies are the only extant member of Thylacomyidae after their closest relative, lesser bilbies (Macrotis leucura), became extinct between the 1930's and 1960's. Like M. leucura, greater bilbies have suffered a significant drop in population over the past 200 years due to the introduction of invasive predators such as dingos, red foxes, and feral cats, and invasive herbivores such as European rabbits. Along with the introduction of invasive species, a number of new diseases have also been brought to Australia. Greater 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. 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 greater bilbies. As well as the reduction of plants through feeding, grazing has also led to the degradation of bilby habitat. Greater bilby habitat is also being destroyed as a result of human development and they are hit by cars along roads. Greater bilbies are protected under Australian law. A number of breeding and reintroduction projects are underway, as well as projects to control populations of harmful invasive species. Since the 1990's, greater 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. Greater bilbies have their own Australian holiday, National Bilby Day, anually held in mid-September in hopes of raising funds and educating the public on bilby conservation. ("National Recovery Plan for the Greater Bilby Macrotis lagotis", 2006; Burbidge, et al., 2008; Department of the Environment, Water, Heritage and the Arts, 2009; Department of the Environment, Water, Heritage, and the Arts, 2004a; Department of the Environment, Water, Heritage, and the Arts, 2004b; Friend, et al., 2008; Hintze, 2002; Northern Territory Government, 2006; Queensland Environmental Protection Agency, 2007)