Macropus irma

Geographic Range

Western brush wallabies are endemic to Australia, with the current range confined to the southwestern coastal region of Western Australia.

• Biogeographic Regions
• australian australian
  • native native

Habitat

Preferred habitat for Macropus irma is open forest or woodlands with seasonally wet sites and low vegetation. This species is often found in dry schlerophyll forests, such as jarrah, and areas of mallee and heathland scrub. It is rarely found in wet schlerophyll forests and is not found in ecosystems characterized by a thick understory, such as karri forests.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• forest forest
• scrub forest scrub forest

Physical Description

Western brush wallabies are gray with slight brown variation in color on the neck and back. The alternative common name, black-gloved wallabies, is derived from the black coloring on the fore- and hind limbs. The most distinctive features of western brush wallabies, and those that are most useful for distinguishing it from western grey kangaroos ( Macropus fuliginosus ), are facial characters. They have two unique white stripes that extend from each of the ears to the end of the rostrum. The pinnae are also black on the exterior and a slightly lighter white or buff color in the interior. The chest is gray, the ventral portion of the abdomen is buff, and the tail has a black crest at its most distal end. Some individuals also have a faint black banded patterning on their dorsal side. Western brush wallabies can further be distinguished from the western grey kangaroos by their smaller size, significantly shorter forelimbs, and distinct gait: they move quickly with the head kept low and the tail extended rather than in an upright posture.

The second largest native mammal in southwest Western Australia, individuals range from 7 to 9 kg and have been reported up to 1530 mm in length. The tail comprises a large portion of this measurement and is between 540 and 970 mm long. Not including the tail, the head and body measurement ranges from 450 to 525 mm. Although size varies within the species, there is no significant observable sexual dimorphism.

As with other macropodids , the hind limbs of western brush wallabies are adapted to fast, powerful, hopping locomotion. The hind foot is slender and lacks a hallux. The second and third digits are fused to form a syndactylous digit, and the fourth digit is elongated and robust. The fourth digit bears the bulk of the energy transferred from the leg to the ground during hopping. Macropodids tend to exhibit a secondary form of slow 'pentapedal' locomotion, whereby the tail is used in conjunction with the forelimbs to support the weight of the body while the hind legs are swung forward.

Basal metabolic rate of Macropus irma is unknown, but marsupials in general tend to have lower basal metabolic rates than eutherian mammals. Some authors have suggested that this is correlated with saltatorial locomotion, which requires less energy than other forms of sustained locomotion.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Reproduction

The mating system of western brush wallabies is not well documented. However, Tammar wallabies ( Macropus eugenii ) are morphologically similar, have a partially overlapping range, are closely related, and have been more extensively studied. Macropus eugenii has a polygynous mating system with clear male dominance hierarchies. Reproductive success is closely correlated with physical size and presumably with success in agonistic interactions. The majority of first copulations with females are achieved by alpha males, with the majority of the offspring also sired by the alpha males that secure the first copulation. Females usually mate with more than one male and subsequent copulations have been observed with males other than the alpha. Tammar wallabies also engage in a variety of behaviors to enhance reproductive success and secure mates. Males mate-guard pre- and post-copulation, check females, and intervene in consortships developing between a female and another male. Alpha males tend to engage in all of these sexual behaviors with greater frequency than lower-ranking males, making social stratification in Macropus eugenii distinct. Males of several macropodid species also make a clucking sound when courting females to attract a mate.

It is, however, important to note that there are distinguishing features between Macropus eugenii and Macropus irma that may have implications for how closely the western brush wallaby mating system resembles that of Tammar wallabies. For instance, Macropus eugenii is sexually dimorphic, common in polygynous species, but Macropus irma does not exhibit sexual dimorphism.

There is little information available in the literature on reproduction in western brush wallabies. Females give birth to a single offspring usually in April or May. The newborn then spends up to 7 months in the pouch attached to one of the mother's 4 teats, after which point it leaves the pouch to suckle occasionally while it accompanies the mother on foot. Embryonic diapause, a period during which hormonal signals delay embryonic development, is common among macropodids and has been noted in Macropus irma . In other closely related seasonal breeders such as Tammar wallabies, females enter post-partum oestrus after giving birth and mate shortly thereafter. The fertilized ovum resulting from this copulation enters embryonic diapause at the blastocyst stage and reenters active embryonic development once the pouch young vacates. The age of sexual maturity is not well known in western brush wallabies, but Macropus eugenii females and males are sexually mature at 8 months and 24 months, respectively.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• viviparous viviparous
• embryonic diapause embryonic diapause

Western brush wallabies give birth to a single offspring. The female then spends a 7 month period carrying the newborn in her pouch and continues to suckle even after it vacates. Furthermore, a female cannot gestate another fertilized egg until after her current suckling offspring is weaned, meaning that she is fully invested in one offspring at a time both physiologically and behaviorally. The reproductive life of Macropus irma has not been formally observed and recorded, but characteristic features of closely related species, such as the polygynous mating system of Macropus eugenii and the tendency for Macropus eugenii males to copulate with multiple females in succession, suggests that parental investment may be almost exclusively maternal for western brush wallabies

• Parental Investment
• altricial altricial
• female parental care female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

The lifespan of Macropus irma has not been widely documented in wild populations or in captivity, and Macropus irma has historically been uncommon in reserves. The closely related Macropus eugenii , however, lives to be about 11 years old, a fairly common age range for most mid-sized macropodids .

Behavior

Western brush wallabies are well adapted to saltatorial locomotion and are terricolous. They are active primarily in the early hours of the morning and in the late afternoon, and tend to rest alone or in pairs in the shade during the hottest hours of the day. Their general activity cycle appears to be more diurnal than that of other wallabies in their geographic vicinity. Very little is known about Macropus irma social structure.

• Key Behaviors
• terricolous
• saltatorial saltatorial
• diurnal diurnal
• crepuscular crepuscular
• motile motile
• sedentary sedentary
• solitary solitary
• social social

Home Range

The home range of this species is not known.

Communication and Perception

Wallabies in general often communicate with hoarse growls and cough-like vocalizations, particularly to communicate aggression. It has been noted that several wallabies also express alarm by stamping their feet on the ground. Soft clucking is common in males attempting to attract mates and for females interacting with their young. The use of pheromones to check females as they approach estrus has also been observed in Macropus eugenii . Western brush wallabies have not been well studied, so specific information is currently unavailable.

• Communication Channels
• visual visual
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Little detailed information has been documented about the diet of Macropus irma , but individuals appear to prefer native grasses and can survive without access to free water for extended periods of time. Wallaby stomachs are divided into four chambers and their ability to ferment and extract nutrients from high-fiber food sources, such as grasses, makes them successful herbivores. Western brush wallabies generally graze for sustenance in open areas.

• Primary Diet
• herbivore herbivore
  • folivore folivore

• Plant Foods
• leaves

Predation

The two primary predators of Macropus irma are introduced red foxes ( Vulpes vulpes ) and humans ( Homo sapiens . Native predators of young may include large snakes and monitor lizards .

Ecosystem Roles

Western brush wallabies are preyed on by red foxes and may influence vegetation through their herbivory. Marsupial mammals are vulnerable to mycobacterial infections and Mycobacterium avium has been noted as a significant disease risk for Macropus irma , particularly among captive populations.

Economic Importance for Humans: Positive

In the early stages of European settlement, Macropus irma was traded in large numbers for fur. Records indicate annual individual sales as high as 122,000 in 1923.

• Positive Impacts
• body parts are source of valuable material

Economic Importance for Humans: Negative

There are no known adverse effects of Macropus irma on humans.

Conservation Status

After successful fox baiting programs instated to elevate population count after the 1970's, Macropus irma has been classified as a species of Least Concern. It has a large, stable population and a relatively wide distribution, including multiple protected areas.

Other Comments

The conservation status of Macropus irma has been particularly affected by the arrival of Europeans and the population dynamics of predator species. Western brush wallabies have been central in an ongoing debate among conservation biologists about the definition of a Critical Weight Range (CWR). It has been the reigning consensus that non-flying, mid-sized Australian mammals have been most affected by European settlement. Traditionally, the Critical Weight Range species were considered those with mean adult body weights of 35 to 5,500 grams. However, reevaluation of the effect of colonization on populations of western brush wallabies has prompted a push to extend this range to 8,000 grams.

Populations of Macropus irma were heavily affected by a substantial increase in the size of fox populations in 1973 and 1974. In two surveys done in 1970 and 1990, researchers observed that, while the population size of western grey kangaroos remained stable, those of Western brush wallabies decreased by approximately 80 %. Other studies reported a population density decrease during the same period from 10 per 100 kilometers to 1 per 100 kilometers. Although land clearance for agricultural purposes has also caused the population to disperse and limited its range, the overall number of individuals has increased in recent years. Population increases have been documented and Macropus irma , among other endangered native animals, seems to be responding well to fox baiting programs.

Additional Links

Encyclopedia of Life

Contributors

Natalie Morningstar (author), Yale University, Eric Sargis (editor), Yale University, Rachel Racicot (editor), Yale University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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Buddle, B., L. Young. 2000. Immunobiology of mycobacterial infections in marsupials. Developmental & Comparative Immunology , 24: 517-529. Accessed April 05, 2012 at http://www.sciencedirect.com/science/article/pii/S0145305X00000148 .

Coulson, G., M. Eldridge. 2010. Macropods : the biology of kangaroos, wallabies, and rat-kangaroos . Collingwood, VIC, Australia: CSIRO Publishing.

Dawson, T. 1974. Recent advances in marsupial physiology (non-reproductive). The Australian Mammal Society Council 1973-1974: 181-188. Accessed April 24, 2012 at http://books.google.com/books?hl=en&lr=&id=yio4AAAAIAAJ&oi=fnd&pg=PA269&dq=Macropus+irma+basal+metabolic&ots=0THxcwiM7S&sig=SOaIwPUZ8VR1YmQrGc95icGaKeg#v=snippet&q=basal%20metabolic%20rate&f=false .

Kitchener, D., A. Chapman, B. Muir. 1980. The Conservation Value for Mammals of Reserves in the Western Australian Wheatbelt. Biological Conservation , 18: 179-207. Accessed April 05, 2012 at http://www.sciencedirect.com/science/article/pii/0006320780900336 .

Menkhorst, P., F. Knight. 2004. Field Guide to the Mammals of Australia . New York, NY: Oxford University Press.

Morris, K., T. Friend, A. Burbidge. 2008. "The IUCN Red List of Threatened Species" (On-line). Accessed February 08, 2012 at http://www.iucnredlist.org/apps/redlist/details/12626/0 .

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