Tree-kangaroos are marsupials of the genus Dendrolagus, uniquely adapted for life in the trees. These fascinating creatures inhabit the tropical rainforests of New Guinea, far northeastern Queensland, Australia, and some islands in the surrounding region. While they share ancestry with terrestrial kangaroos, tree-kangaroos have evolved specialized features for an arboreal existence. This article delves into the dietary habits of these intriguing animals, exploring what they eat and how their diet contributes to their survival in the rainforest canopy.
Evolutionary History and Adaptation
The evolutionary journey of tree-kangaroos possibly began with a rainforest floor-dwelling pademelon-like ancestor. This ancestor may have evolved from an arboreal possum-like ancestor, a theory suspected for all macropodid marsupials in Australia and New Guinea. During the late Eocene, the drying of the Australian/New Guinean continent caused a retreat of rainforests, forcing ancestral pademelons to adapt to drier, rockier environments. Over generations, these pademelons may have evolved into rock-wallabies (Petrogale spp.), which developed a generalist feeding strategy due to their dependence on diverse vegetation refuges. This adaptability allowed rock-wallabies to easily transition to Malesian rainforest types introduced to Australia from Asia during the mid-Miocene. The rock-wallabies that migrated into these introduced forests adapted to spend more time climbing trees.
Dietary Preferences
Tree kangaroos are herbivores. The main diet of the tree-kangaroo consists of leaves and fruit gathered from the trees, but they occasionally scavenge from the ground.
Wild tree kangaroos in Papua New Guinea had significantly higher values for vitamin E than captive individuals in one study.
Specific Food Preferences
- Leaves: Tree-kangaroos spend hours foraging in their arboreal habitat for foliage.
- Roots: Roots form a part of their diet.
- Seasonal Fruits: They consume seasonal fruits.
- Bark: Bark also forms a part of their diet.
Tree-kangaroo Species
There are currently 14 known species of tree kangaroos:
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- Bennett’s tree-kangaroo (Dendrolagus bennettianus)
- Buergers' tree kangaroo
- Dingiso (Dendrolagus mbaiso)
- Doria’s tree-kangaroo (Dendrolagus dorianus)
- Golden-mantled tree-kangaroo (Dendrolagus pulcherrimus)
- Goodfellow’s tree-kangaroo (Dendrolagus goodfellowi)
- Grizzled tree-kangaroo (Dendrolagus inustus)
- Huon tree-kangaroo (Dendrolagus matschiei)
- Ifola (Dendrolagus notatus)
- Lowlands tree-kangaroo (Dendrolagus spadix)
- Lumholtz’s tree-kangaroo (Dendrolagus lumholtzi)
- Matschie's tree-kangaroo
- Seri’s tree-kangaroo (Dendrolagus stellarum)
- Tenkile (Dendrolagus scottae)
- Vogelkop tree-kangaroo (Dendrolagus ursinus)
- Wondiwoi tree-kangaroo (Dendrolagus mayri)
Physical Adaptations for Arboreal Life
Tree-kangaroos have several adaptations suited to their arboreal lifestyle. Compared to terrestrial kangaroos, they have longer and broader hind feet with longer, curved nails, and a sponge-like grip on their paws and soles of their feet. Tree-kangaroos also have a much larger and more pendulous tail than terrestrial kangaroos, giving them enhanced balance while moving about the trees.
Locomotion
While locomotion on the ground is by hopping, as with true kangaroos, tree-kangaroos are slow and clumsy. They move at approximately human walking pace and hop awkwardly, leaning their body far forward to balance the heavy tail. However, in trees, they are bold and agile, climbing by wrapping their forelimbs around the trunk of a tree and hopping up using their powerful hind legs.
Habitat and Distribution
Tree-kangaroos inhabit the tropical rainforests of New Guinea, far northeastern Australia, and some of the islands in the region, including the Schouten Islands and the Raja Ampat Islands. Most species are found in mountainous areas, although some, like the aptly named lowlands tree-kangaroo, also occur in lowlands.
Here’s a breakdown of where you can find each of the tree kangaroo species:
- Australia: Bennett’s tree kangaroo and Lumholtz’s tree kangaroo
- Papua New Guinea: Ifola tree kangaroo, Tenkile tree kangaroo, Doria’s tree kangaroo, lowlands tree kangaroo, and Huon tree kangaroo
- Indonesia: Dingiso tree kangaroo, Vogelkop tree kangaroo, and Wondiwoi tree kangaroo
- Both Papua New Guinea and Indonesia: Seri’s tree kangaroo, grizzled tree kangaroo, golden-mantled tree kangaroo, and Goodfellow’s tree kangaroo
These rainforests provide the perfect home for tree kangaroo’s arboreal lifestyle. Compared to kangaroos found on the ground, tree kangaroos have longer forearms and shorter hind legs. Unlike terrestrial kangaroos, tree kangaroos can move their hind legs separately, which aids them in their climbing movements, as well as hopping. Tree kangaroos also have rough pads on their fore and hind feet, as well as long claws which help them grip trees.
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Conservation Status and Threats
Most tree-kangaroos are considered threatened due to hunting and habitat destruction. Tree-kangaroo habitats are being destroyed or replaced by logging and timber production, along with coffee, rice, and wheat production. This habitat loss can make tree-kangaroos more exposed to predators, such as feral domestic dogs. Hunting by local community members also contributes markedly to the declines in tree-kangaroo populations.
According to the IUCN Red List, tree kangaroos range from near threatened to critically endangered across the various species:
- Near threatened: Lumholtz’s tree kangaroo, Bennett’s tree kangaroo
- Vulnerable: Doria’s tree kangaroo, lowlands tree kangaroo, Vogelkop tree kangaroo, Seri’s tree kangaroo, grizzled tree kangaroo
- Endangered: Huon tree kangaroo, Goodfellow’s tree kangaroo, dingiso tree kangaroo, ifola tree kangaroo
- Critically endangered: Tenkile tree kangaroo, Wondiwoi tree kangaroo, golden-mantled tree kangaroo
Reproduction and Life Cycle
Little is known about the reproduction of tree-kangaroos in the wild; the only published data are from captive individuals. Female tree-kangaroos reach sexual maturity as early as 2.04 years of age, and males at 4.6 years. The female's fertile period is estimated to be approximately two months.
Female tree kangaroos have a gestation period of only 44 days. When the underdeveloped, kidney-bean-sized joey is born, it crawls into the pouch where it will latch onto a teat and continue to grow for three months. The joey remains in the pouch until about 7 months. The mother will clean her pouch and groom her joey often during this phase. After the joey initially leaves the pouch at about 7 months, it will continue to return to the pouch to nurse. This "in and out" phase lasts for about three months, and the joey is completely out of the pouch at 10 months and weaned after about 13 months.
Role in the Ecosystem
Tree kangaroos play an important role in maintaining the ecological balance of their arboreal habitats. As they move through the trees, they aid both pollination and seed dispersal, which is critical to the regeneration, functioning, and resilience of forests. This is particularly important given how beneficial rainforests are to the Earth’s ecosystem. Not only do they capture and store carbon, helping mitigate climate change, but they’re also critical to local communities, as these ecosystem services help provide food, water, and shelter.
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Conservation Efforts
To safeguard these fascinating animals and the biodiversity of rainforests, more conservation efforts are needed.
The Tree Kangaroo Conservation Program has established the YUS Conservation Area in Papua New Guinea to help protect the Matschie’s tree kangaroos.