Kangaroos are marsupials and belong to the Family Macropodidae (i.e. big feet) that is grouped with the Potoroidae (potoroos, bettongs, rat-kangaroos) and Hypsiprymnodontidae (musky rat-kangaroo) in the Super-Family, Macropodoidea. This comprises around 50 species in
The ancestor of the kangaroos and their kind was possum-like and descended from the trees to spawn a large and diverse fauna of browsers and grazers. Curiously one group the Tree-kangaroos ascended the trees again to exploit the large foliovore (leaf-eating) niche in the tropics of Australia and Papua New Guinea (PNG) occupied by primates like Proboscis Monkeys in nearby Indonesia. Thus the Tree-kangaroos are in many respects the closest animals we have to monkeys in the Australo-Papuan region. Unfortunately for Tree-kangaroos their meat is tasty (hence the genus Dendrolagus or tree-hare given by the Dutch) and hunting along with habitat destruction and climate change are significant threats. Thus the majority of species are threatened or vulnerable under IUCN Red List classification.
The centre of diversity of the Tree-kangaroos is PNG rather than Australia. Eight species are recognised in PNG and probably more remain to be formerly described by taxonomists. The Tenkile (Dendrolagus scottae) was described by Flannery and Seri as recently as 1990. Two species are found in tropical north Queensland in Australia. The larger is Bennett's Tree-kangaroo described by De Vis in 1887 and named in honour of Dr George Bennett of the Australian Museum in Sydney. The smaller species is Lumholtz's Tree-kangaroo described by Collett in 1884 and named after Rev. Carl Lumholtz a collector sponsored by the University of Christiana in Norway.
The body form of the terrestrial kangaroos (ancestral to the Tree-Kangaroos) is a reduction in the fore-limbs and an accentuation of the hind-limbs for locomotion. The body form of Tree-kangaroos sees a more equal distribution of body mass and musculature in the fore and hind parts. The fore-arms are large and well-muscled to assist climbing and the fore-paws are strongly clawed with pronounced curvature in the claws. The fore-paw aids tree-climbing but also is used to grasp and manipulate food. The hind-limbs remained enlarged but the feet are short, very broad and have a long curved claw on each digit. The pad on both hind and fore-feet is fleshy with prominent tuberculations that aid grip when climbing. The ankle allows more degrees of movement than a terrestrial kangaroo and presumably also aids climbing. The tails of the Australian Tree-kangaroos are very long and exceed the head-body length. They appear to be used as a counterbalance and vary in placement from over the body in sedate hopping to rigidly out when rapidly fleeing. The ears are relatively reduced to small bear-like proportions in contrast to the large terrestrial kangaroos.
Dendrolagus bennettianus ('Bennett's tree-hare')
Cedar Bay (Mangkal-Mangkalba) National Park, Queensland
Cedar Bay is a remote coastal park south of Cooktown in north Queensland. The Park falls within the Wet Tropics World Heritage Area. The coastal beach is backed by a rainforest of tulip oaks, Daintree pendasm cycads, fan palms and milky pines. The area was mined for tin but not extensively logged and so much remains relatively pristine. Bush camping is allowed in the Park which has no supporting facilities. Users must book and pay in advance at the Queensland Parks and Wildlife Service offices in Cooktown or Mossman. There is a walking track for fit hikers and the Bennett's Tree-kangaroo is best seen at night so walkers should be well-prepared for night observations in a remote location.
The Park is accessible by walking or boat only and the walking trail commences on private property at the Home Rule Rainforest Lodge (www.home-rule.com.au) which provides accommodation, meals and overnight camping by prior arrangement.
The Tree-kangaroo Group (www.tree-kangaroo.net) provide the following tips for spotting Tree-kangaroos.
- They are small objects (dog sized), very hard to spot and may be high in the tree canopy. The long pendulous tail is the best cue.
- Looking up into the tree canopy is inferior to looking as horizontal as possible into it. Thus find high ground in sloping terrain and look into canopy.
- Overcast drizzling rain is a good time to spot Tree-kangaroos as they come to the edges of branches rather than remaining in dense foliage. Heavy rain causes them to shelter in dense foliage and they will be difficult to see.
- Late afternoon and early evening herald the start of the night active period and are good times to see females.
- Night spotlighting is possible with a dull ruby red eyeshine that is less intense than possums. Tree-kangaroos are skittish at night and will readily retreat from the spotlighter.
Bennett's Tree-kangaroo is found in north-east Queensland north of the Daintree River and Cairns. They range across a variety of closed forest habitat from coastal lowlands, moist monsoon forest up into the montane rainforest. There presence in lowland forest potentially makes them easy to find but they are extremely shy towards people. One recommendation is not to look in the moist rainforest on the east coast but rather go to the sparser and drier gallery forest on the western edge of the species range.
The diet of Bennett's Tree-kangaroo has been well-studied but due to their shyness this has mainly been indirect through examination of faecal pellets, identification of plant fragments and analysis of their dietary qualities. They eat mainly young foliage (leaves) from about 33 species of plant including 19 tree species and 12 vine species. The foliage of Daintree Hickory (Ganophyllum falcatum) is particularly eaten and has a slight nutty taste to the human palate. They also eat fruit from several species including native 'olives' (Chionanthus ramiflorus, Olea paniculate), figs and the Native Longan (Dimocarpus australianus). Of these the latter are sweet and tasty to people.
Analysis of the nutrient concentrations of the foliage eaten by Bennett's Tree-kangaroo shows a higher quality than the eucalypt species favoured by Koalas and Possums living in drier habitats.
Adult individuals of the same sex do not typically share home ranges but those of males and females overlap. Males will fight to exclude other males from their home range but females may associate with more than one male. Thus males are usually solitary in the daytime but associate with females in their home range (e.g. three in a radio-tracking study) during the foraging period at night. However, given the females are spatially segregated the male does not have exclusive dominion as a neighbouring male may associate with an unguarded female. The male strategy is presumably to check 'his females' regularly and take precedence in mating when they are in oestrus.
Breeding is seasonal and cued to the Wet season with most pouch young born in the early Wet (November-January). In other respects, the reproductive pattern is similar to other macropods but embryonic diapause is unlikely. The reproductive pattern of Lumholtz's Tree-kangaroo is better studied.
Bennett's Tree-kangaroos will be typically seen alone but resident males and females whose home ranges overlap may associate as a pair over the night-time foraging period. Females may share their home range with recent offspring after weaning and associations as long as 2.5 years are known. Males are intolerant of other males and have a reputation of being particularly pugnacious with scars and damaged ears as evidence of fighting. Thus male home ranges are defended territories unlike most terrestrial macropods.
Martin, R (2005) Tree-kangaroos of Australia and New Guinea. (CSIRO Publishing: Melbourne).