Macropus irmawestern brush wallaby

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Geographic Range

Western brush wallabies are endemic to Australia, with the current range confined to the southwestern coastal region of Western Australia. (Turner, 2004)

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. (Strahan, 1995; Turner, 2004)

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. ("Current Projects", 2012; Dawson, 1974; Menkhorst and Knight, 2004; Strahan, 1995; Turner, 2004)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    7 to 9 kg
    15.42 to 19.82 lb
  • Range length
    830 to 1530 mm
    32.68 to 60.24 in

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. (Coulson and Eldridge, 2010; Menkhorst and Knight, 2004)

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. (Coulson and Eldridge, 2010; Nowak, 1999; Strahan, 1995; Turner, 2004)

  • Breeding interval
    Breeding interval in western brush wallabies is not documented and may vary by seasonal and unpredictable conditions, such as the availability of food.
  • Breeding season
    Females typically give birth in April or May.
  • Average number of offspring
    1

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 (Coulson and Eldridge, 2010; Strahan, 1995)

  • Parental Investment
  • altricial
  • 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. (Kitchener, et al., 1980; Turner, 2004)

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. (Strahan, 1995; Turner, 2004)

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. (Coulson and Eldridge, 2010; Menkhorst and Knight, 2004)

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. (Strahan, 1995; Turner, 2004)

  • 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. (Morris, et al., 2008)

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. (Buddle and Young, 2000; Morris, et al., 2008)

Commensal/Parasitic Species
  • Mycobacterium avium

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. (Morris, et al., 2008)

  • 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. (Morris, et al., 2008)

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. ("Action Plan for Australian Marsupials and Monotremes", 2011; Armstrong and Batini, 1997; Strahan, 1995; Turner, 2004)

Contributors

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

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

diurnal
  1. active during the day, 2. lasting for one day.
embryonic diapause

At about the time a female gives birth (e.g. in most kangaroo species), she also becomes receptive and mates. Embryos produced at this mating develop only as far as a hollow ball of cells (the blastocyst) and then become quiescent, entering a state of suspended animation or embryonic diapause. The hormonal signal (prolactin) which blocks further development of the blastocyst is produced in response to the sucking stimulus from the young in the pouch. When sucking decreases as the young begins to eat other food and to leave the pouch, or if the young is lost from the pouch, the quiescent blastocyst resumes development, the embryo is born, and the cycle begins again. (Macdonald 1984)

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

2011. "Action Plan for Australian Marsupials and Monotremes" (On-line). Wildlife Australia. Accessed February 15, 2012 at http://www.environment.gov.au/biodiversity/threatened/publications/action/marsupials/index.html.

2012. "Current Projects" (On-line). Cape to Cape Catchments Group. Accessed April 08, 2012 at http://www.capetocape.org.au/ccg-programs/biodiversity/current-projects/.

Armstrong, R., F. Batini. 1997. Western Shield — Bringing back wildlife from the brink of extinction. Fauna Habitat Reconstruction After Mining: 91-98. Accessed April 08, 2012 at pubs.iied.org/pdfs/G00569.pdf.

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.

Nowak, R. 1999. Walker's Mammals of the World (Volume I). Baltimore: Johns Hopkins University Press.

Strahan, R. 1995. Mammals of Australia. Washington, DC: Smithsonian Institution Press.

Turner, J. 2004. Mammals of Australia: [an introduction to their classification, biology and distribution]. Sofia, Bulgaria: Pensoft.