Tree-kangaroos
The rainforests of Australia’s north Queensland region are home to two species of Tree-kangaroo; Lumholtz’s (Dendrolagus lumholtz’s) and Bennett’s (Dendrolagus bennettianus) A further dozen or so species, so far described, occur in the rainforests of Papua New Guinea and West Papua.
Bennett’s Tree-kangaroo is mainly found in the rainforest and sclerophyll woodlands north of the Daintree River as far as Cooktown. Like Lumholtz’s the species appears to be extending its range, the result of cessation of hunting by Aborigines. In recent years there have been sightings by an experienced observer, from around 800 metres elevation on Mt: Lewis, south of the Daintree River.
In size Lumholtz’s Tree-kangaroo is considered to be the smallest of the genus Dendrolagus. Males can weigh up to 10-12 kilos. Females to 8-9 kilos. Bennett’s is a much larger animal with males weighing up to 12-14 kilos and females up to 12 kilos. Unlike their ground-dwelling counter-parts, tree kangaroos have muscular, short hind limbs and longer forelimbs, an adaption to an arboreal existence. The animals are thick-set and solidly-built and have a long, flexible tail which is used as a counter-balance. It is not prehensile. Their paws are broad and thickly padded and have well-developed crampon-like claws which allow the animal to climb with ease with a ‘grip and kick-like’ motion. They are able to move either bipedally along large horizontal branches, using the tail as a counter-balance, or quadrupedally depending on the situation. Their ankle joints have also evolved to allow for greater dexterity better suited to clambering around in the canopy. Tree-kangaroos can move their hind limbs independently of each other unlike most terrestrial kangaroos. Once in the canopy the animals are somewhat ungainly and awkward. Descending a tree is also awkward and tree-kangaroos come down backwards, an indication that the animal is not fully adapted to an arboreal existence.
Lumholtz’s Tree-kangaroo can be found in most upland and highland rainforest areas on the Atherton and Evelyn Tablelands. The greatest concentrations are to be found in rainforests growing on rich, basalt soils. Their range extends as far north as the Daintree River and appears to be expanding. In recent years there have been a number of photographic records of animals in some lowland, urban areas along the coast near Cairns. In the Ravenshoe/Misty Mountains region, above 900 metres elevation, we have observed several individual animals and family groups living quite happily in sclerophyll forests many kilometres from the nearest rainforest. The family groups included females with large pouch young.
Tree-kangaroos form loose family groups comprising 4-5 females with young and a dominant male. The male establishes a territory which he will defend against all other males. Fights are known to be savage and bloody. They are known to kill rival males and even their own male offspring.
Tree-kangaroos usually produce a single offspring but on one occasion we found a female Bennett’s with two very large pouch joeys. We have also seen Lumholtz’s Tree-kangaroo females on the Atherton Tablelands and in the Misty Mountains with twin pouch young.
Tree-kangaroos evolved from a rock-wallaby ancestor; an animal that was accustomed to climbing around near vertical rocky outcrops and cliff faces. Escaping a terrestrial predator or untapped food resources (or other less obvious pressures) encouraged the rock-wallaby to climb up into the trees and take up a life in the canopy. We have often seen Rock-wallabies venturing up into trees to forage on leaves or fruits.
Tree-kangaroos are mostly folivores. In addition to a wide variety of leaves, we have observed them feeding on the petioles and the sappy bark of Millaa Millaa Vine (Elaeagnus triflora), rainforest mistletoes, the spore fronds of epiphytic ferns (Elkhorn and Staghorn) and lichen and moss-covered bark. They also feed on rainforest fruits and particularly figs, and have also been known to feed on cultivated mangos and stone-fruit.
While on an evening ‘spotlighting’ tour with a ‘zoo’ group a few years ago, we visited a small Cluster Fig tree (Ficus racemosa) on the edge of the rainforest. We had seen two tree-kangaroos there a few nights before so were hopeful of seeing them again. We were somewhat surprised when we found seven tree-kangaroos and two Coppery Brushtail Possums feeding on the barely ripe fruits.
Predators of Tree-kangaroos are many. They include Wedge-tailed Eagles, Dingos/wild dogs, Amethystine and Carpets Pythons and Spotted-tailed Quolls. We have seen Rufous Owls on several occasions with large Brushtail Possum prey so this formidable predator would easily be capable of taking small out-of-pouch joeys.
Since 1992 we have had a number of interesting observations involving Wedge-tailed Eagles attacking tree-kangaroos. Many of these observations have been while we were out on tours with clients on the Atherton Tablelands and in the Misty Mountains.
One method employed by these huge raptors (see Wedge-tailed Eagle header image on ‘Contacts’ page) appears to be similar to that used by Verreaux’s Eagle of Africa, when hunting Rock Hyrax. The birds hunt as a pair. One bird appears in full view to draw the attention of the quarry, while the other slips in, undetected, from beneath or behind and snatches the unfortunate victim. This hunting strategy by a pair of Wedge-tailed Eagles has been observed several times.
On one occasion we were with an international film crew that was making a documentary on the evolution of tree-kangaroos. While filming one morning we observed a pair of eagles attacking an adult female tree-kangaroo with a small, out-of-pouch joey. It had been a very cold night and the two animals were sunning themselves in the early morning sun on the top of a vine covered tree. The female was clearly watching the eagle that was flying in circles about 100 metres in front of her and over a field adjoining the rainforest. The female tree-kangaroo began making a very audible clicking sound which we took as an alarm call. A second eagle suddenly appeared low and fast along the side of the field and came up underneath the tree where the two tree-kangaroos were sitting. Both animals jumped and escaped the eagle’s talons by a whisker.
While out on a tour with clients one afternoon we observed another incident with a Wedge-tailed Eagle. We had been watching a tree-kangaroo with a small joey sitting on an open branch, very high up and just below the rainforest canopy, when an eagle suddenly appeared overhead and dived through the canopy and landed on a branch about 8-metres from the tree-kangaroos. The female tree-kangaroo immediately jumped (from about 25 metres) but the joey just sat and called for its mother. The eagle was unable to fly at the joey because of the tangle of branches so proceeded to scramble through the canopy, jumping from branch to branch. The terrified joey jumped at the last second and crashed to the ground. Both mother and joey appeared about a week later in the same tree.
On another occasion, while overlooking the rainforest canopy at Warrigal Highland Rainforest Preserve, we observed a Wedge-tailed Eagle diving into the rainforest canopy. After about half an hour the eagle reappeared, struggling to carry the body of a well-grown, young Lumholtz’s Tree-kangaroo. Through binoculars we were easily able to see that the animal appeared freshly killed and partly eaten around the neck.
Populations of both Lumholtz’s and Bennett’s Tree-kangaroos appear to be reasonably secure at present. Much of their remaining habitat is protected by a World Heritage listed covenant and is in a national park or other protected area. Habitat outside these areas is mostly steep and rugged and unsuitable for agriculture or broad-scale timber extraction.
