lumholtz’s tree-kangaroo: conserving a rare...

Lumholtz’s Tree-Kangaroo:Conserving a rare marsupial

May 1999

Left: Graeme Newell radio-tracks an adultmale tree-kangaroo (photo Peter Trott)Right: Graeme fitting a radio-collar to ananaesthetised tree-kangaroo. Animalsrecover within two hours and are released atthe same site they were captured (photoGraeme Newell)Below: Loss of habitat from land clearingrepresents one of the greatest threats to thetree-kangaroo’s survival (photo Peter Trott)

We know a great deal about the koalaand other cute creatures of Australia,but tree-kangaroos are elusive animalsthat keep well hidden in the rainforestcanopy and have maintained a degreeof mystique. Tree-kangaroos are rarewhere they exist in the tropical rainfor-ests of Australia and New Guinea,relying on the fragile and swiftlydiminishing tropical rainforest environ-ment for their survival. As land contin-ues to be cleared for crops and grazing,it is important to understand theirecology so we can conserve these rarearboreal marsupials. How does the tree-kangaroo respond and adjust tochanges in its environment, such asland clearing, and which specificdangers pose the greatest threat to itssurvival?

Graeme Newell began his search foranswers during a post-doctoral

fellowship at CSIRO’s Tropical ForestResearch Centre in Atherton, Queens-land. His study focussed on Lumholtz’sTree-kangaroo (Dendrolagus lumholtzi),one of only two species of tree-kangarooin Australia. Found only in the tropicalrainforests and adjacent forest commu-nities of North Queensland, Lumholtz’sTree-kangaroo lives in rugged andinaccessible rainforest areas includingwithin forest remnants on the AthertonTableland. These isolated forest blocksprovide an important setting to studyhow these rare animals survive in afragmented landscape.

Objectives of the research

Graeme wanted to find out: how theresident animals used their habitat;whether they moved regularly to otherfragments nearby; which tree speciesthey preferred to use and which other

features of the environment wererequired. This information would assistin identifying high-quality forest areasfor their future conservation, and beincorporated into local tree-plantingschemes to accommodate more tree-kangaroos in the future.

Playing hide and seek

The study site chosen was well-knownto locals for its population of tree-kangaroos. The 20-hectare block ofmixed remnant/regrowth forest was onprivate land near Yungaburra on theTablelands, about 70 kilometres inlandfrom Cairns and 760 metres above sealevel. Tree-kangaroos may be easilystressed by capture, and to reduce thechance of this, the animals were anaes-thetised while radio collars were fitted.Darting the animals proved successfuland soon Graeme was collecting dataon between seven and ten animals atany one time, using a hand heldantenna and telemetry receiver. Herecorded time of day, position in theforest and the species of trees and vineseach animal was

associated with. This enabled him toestablish how much space the animalsused, how the animals interacted witheach other and which tree species theanimals used regularly.

Graeme found that even with radio-signals identifying the presence of atree-kangaroo in the tree canopy, theyoften remained invisible, sometimes inquite sparse foliage - a very clear in-dication of just how cryptic they can be.

Responding to a changingenvironment

After several months the study took adramatic turn when the landownerinformed Graeme he would be clearinghalf the forest block for grazing. Whilethe results were likely to be distressingfor both the tree-kangaroos and theresearcher, this provided a uniqueopportunity to observe how arborealanimals responded directly to loss oftheir habitat. It seemed logical landclearing would force these tree-dwell-ing, shy animals to seek out new homeranges. The results were surprising.

Five male and six female collared tree-kangaroos whose ranges fell within the10 cleared hectares did not move awayfrom the area. Instead they continued touse their original home range despitethe area having been flattened by thebulldozer. While the tangle of fallentrees provided somewhere to live andprotection for some from predators,others quickly fell prey to dingoes anddogs.

Those that escaped predation had otherdangers to contend with, such as adiminished food supply, and wouldlikely need to eat potentially toxic

plants rather than their standard fare ofleaves from rainforest trees and vines.Overall, it became obvious thatLumholtz’s Tree-kangaroos were veryreluctant to leave their homes, exceptperhaps for young male animals yet toestablish a permanent home range.

A clearer picture emerges

The study found that Lumholtz’s Tree-kangaroo:_ shows an apparent preference for

trees such as Black Bean orMoreton Bay Chestnut, Candlenut,Grey Bollywood and Milky Pine,and the spiny vine known asCockspur Thorn;

_ uses small home ranges within theforest fragments - females generallymaintain exclusive and non-overlapping ranges of around 0.7hectares, while males roamed overan average of 1.8 hectares, whichcould overlap several female andmale ranges;

_ become vulnerable to predation,loss of condition and starvation, aswell as other causes of fatality, onceclearing occurs;

_ are highly territorial animals thatare reluctant to abandon their homeranges following a severe distur-bance. This may suggest thatrelocating tree-kangaroos intoforest blocks with existing tree-kangaroos could lead to conflictbetween the animals, but thisrequires further investigation;

_ mostly live a sedentary life. Malesoccasionally move between forestblocks, possibly following antago-nistic encounters with other males,but females rarely move from theirhome patch. This has been rein-forced by recent genetic test results

conducted on the animals at thisfragmented study site which showthe female tree-kangaroos are allrelated to either of two original‘founder’ female tree-kangaroos.

Issues for conservation

Three important issues stand out inspecies conservation:

Road deaths are frequent in some areasas the animals move between forestareas, accounting for the loss of up to adozen animals per annum - a significantnumber when viewed in terms of theirapparent low rate of reproduction, inaddition to loss from other causes.

Increased control of predators such asdingoes and dogs may be necessary inareas adjacent to tree-kangaroo habitats,especially when these habitats are nearresidential areas.

Relatively small plots of rainforest onfreehold land, unallocated State Landand land controlled by Local ShireCouncils or other government bodiesmay provide important habitat for tree-kangaroos.

A more effective strategy in promotingtree-kangaroo populations may be therevegetation of suitable areas not viablefor agriculture, providing corridorsbetween strategic blocks of preservedforest fragments.

For further information:Dr Graeme Newell, Arthur RylahInstitute for Environmental Research,DNRE, 123 Brown Street, Heidelberg,Victoria, 3084. Phone: (03) 9450 8600,email: graeme.newell@nre.vic.gov.au