Study: What do Tree Kangaroos really like to eat?

A recently published study by the Tree Kangaroo Conservation Project (TKCP) in Morobe’s Huon Peninsula in PNG has identified the native food plants of the endangered Matschie’s Tree Kangaroo, providing an important dietary insight for captive-managed populations.

When visiting zoos and other places where animals are kept we often see this sign: “Please Don’t Feed the Animals”.

This important notice is to protect the public from any danger the wild animal may pose, and also to safe-guard the animals from any food offered by the public which may be harmful for the animal’s health.

Animals kept in captivity in zoos and other institutions such as the Port Moresby Nature Park, living outside their natural habitat and unable to access food they would normally eat in the wild, are fed formulated diets that aim to closely resemble their natural foods and which meet their daily nutritional requirements.

One such animal that is very endearing to the public and found in zoos throughout the world is PNG’s endangered Matschie’s Tree Kangaroo (Dendrolagus matschiei).

This golden-brownish marsupial, one of PNG’s 10 Tree Kangaroo species, is endemic to the montane forests of YUS (named after the Yopno, Uruwa and Som rivers) area of the Huon Peninsula of Morobe Province, and was previously under threat from habitat destruction and overhunting for food and cultural purposes.

It is now the flagship species of the YUS Conservation Area and the Tree Kangaroo Conservation Program (TKCP), who aim to protect the animal in its natural habitat.

The YUS Conservation Area is PNG’s first nationally-recognized conservation area and owes its establishment to the TKCP’s work, under the Directorship of US Conservation Scientist Dr. Lisa Dabek, to preserve this endangered animal with the help of its traditional custodians, and also provide the local communities with sustainable livelihood development projects.

As part of this conservation effort and to promote its plight, Matschie’s Tree Kangaroo individuals are kept in 21 North American zoos, 2 facilities in Europe, and 2 in PNG.

Sadly, however, due to the absence of studies on native food plants’ nutrient and mineral composition to inform and regulate the diets of captive-managed tree kangaroos, several diet-related health issues have arisen.

For example, captive animals weigh considerably more (up to 50 percent) than healthy individuals found in the wild. Captive populations are also reported to be declining, with low reproduction rates in prime breeding females.

Just this month, PNG and international researchers published a significant journal article documenting the types of forest plants that the Matschie’s Tree Kangaroo normally eats in its natural habitat. These plants are referred to as “browses”, and the animal’s act of eating them is termed as “browsing”.

Titled, ‘Composition of browses consumed by Matschie’s tree kangaroo (Dendrolagus matschiei) sampled from home ranges in Papua New Guinea’, this study was published in the international journal Zoo Biology, and aims to “provide useful information that can be used to adjust nutrient targets for dietary development and feeding management of captive populations of tree kangaroos.”

The study was initiated and partially-funded by the American Association of Zoos and Aquariums’ (AZA) Tree Kangaroo Species Survival Program (TKSSP), whose dedicated field project is the Tree Kangaroo Conservation Program (TKCP) in PNG.

The two PNG researchers involved in the study are Mr. Daniel Okena and Mr. Oliver Paul, who are specialized in Mammalogy (study of mammals) and Botany, respectively. Mr. Okena is currently pursuing a Master of Philosophy (MPhil) degree studying mammal ecology in PNG.

Using field data from observing the species in its habitat for the past 20 years, the researchers and landowners, like Mr. Eki Nimoniong, have collected and documented 26 different food plants that the Matschie’s Tree Kangaroo normally eats, out of an estimated 90-plus species the local landowner trackers/hunters have identified. These include ferns, shrubs, vines, orchids and other plant and tree leaves, and are most likely to be species only found in the YUS area’s rugged mountains at 3000m above sea level.

The lengthy study period taken to accumulate these data can be attributed to the animal’s shy, solitary, and mostly tree-dwelling behavior; its small, slow-breeding, scattered populations; and difficulties in tracking and observing it in its mountainous and thickly-forested home range.

These 26 plant samples were identified at the PNG National Herbarium in Lae and later sent for nutrient and mineral composition laboratory analyses in the USA.

The laboratory analyses found that the native food plants contained high fiber content, low protein, and moderate levels of non-fiber carbohydrates.

Much of the fiber contained in the Matschie’s Tree Kangaroo diet comes from orchids, a common plant group found in its montane habitat.

When comparing these results with a 2015 survey of the diets provided by zoos and similar institutions worldwide for their captive-managed tree kangaroos, the study revealed that the native food plants contained “ 5× the fiber, and half the protein, fat and non-fiber carbohydrate concentrations calculated from captive diets offered, including negligible quantities of starch”.

From these findings, the study suggests the careful control of high-starch diets such as manufactured grain products as well as most vegetable foods.

Instead, edible plant leaves (including branches and twigs) have been recommended as an important source of fibrous nutrition for these animals, which cannot be sufficiently replaced if they are fed other leafy greens sourced domestically.

Tree kangaroos are “fore-gut fermenters” and their stomachs are designed to slowly digest high-fiber plants to provide them their primary energy. This process also allows their vital gut microbes to produce high quality protein that contributes to the total protein required by the marsupial.

As such, feeding them simpler carbohydrates such as sugars and starches that are easily digested may lead to frequent feeding requirements and the risk of obesity in captive animals.

Furthermore, the study showed that trace amounts of minerals such as Manganese and Zinc that are found in their food plants, are also important in sustaining their health.

The study’s lead author, Dr. Ellen S. Dierenfeld, a US-based Comparative Animal Nutritionist with a wildlife nutrition career spanning over 30 years, stated that utilizing nature’s nutrients as a guide for developing diets for creatures under human care has been an important focus in her work.

“Like all herbivores, the high fiber, low starch/sugar, and moderate protein concentrations analyzed in these native foodstuffs reflect the nutrient levels that tree kangaroos and their symbiotic gut microbes evolved with to utilize for optimal health. The added mineral nutrient data from the native food plants provide even further guidelines underlying improved diet formulation.”

“Proper nutrition is a basic foundation of health and reproduction of any species. Thus, habitat conservation to ensure appropriate and adequate food plants are available on-site is critical for survival in nature. But also utilizing information from those resources – in this case, chemistry of dietary ingredients- contributes importantly to off-site species conservation efforts”, Dr. Dierenfeld said.

Dr. Dierenfeld also stated that some of the identified health issues in managed tree kangaroo populations could be alleviated using information gleaned from these types of collaborations, contributing positively to health, welfare, and ultimately, long term survival of the species.

Being the first diet analysis of wild tree kangaroos in PNG, the study is valuable in evaluating the diets of captive animals living outside their native habitat, said Ms. Jacque Blessington, the Tree Kangaroo Species Survival Program (TKSSP) Program Advisor and an important contributor to the study.

“Facilities in North America do not have access to browse species that would be found in PNG, but by analyzing those varieties we can, at a minimum, look at what the diet composition should replicate or, at least, consider”, Ms. Blessington stated.

She added that the TKSSP was also analyzing browse samples from North American facilities to identify plants that could resemble the animal’s native PNG browses in nutrient and mineral composition, with the project’s ultimate goal of re-evaluating and potentially re-formulating diets that are being offered to tree kangaroos in the US and other facilities.

“While we can’t replicate based on plant species, hopefully we can achieve a diet that is balanced and better suited to their natural biology as browsers that eat, primarily, leaves along with bark and moss”, Ms. Blessington said.

Mr. Brett Smith, Curator of the Port Moresby Nature Park, which has several individuals of the Matschie’s Tree Kangaroo in its care, also welcomed the study’s finds.

Mr. Smith has worked with Tree Kangaroos for over 30 years and once volunteered with Dr. Lisa Dabek’s TKCP team in the Huon Peninsula.

He noted that from his experience, diets of captive tree kangaroos varied among different institutions but hoped that the TKCP’s work would result in a better understanding of the dietary requirements needed to care for the animals and enhance their welfare in captivity.

“We have long known that giving tree kangaroos more browse species in their captive diet better replicates what they feed on in the wild and the Port Moresby Nature Park is lucky that we can do this as we work in their home range and have access to many of their wild food sources”, Mr. Smith said.

He said that while it was difficult for facilities overseas that keep tree kangaroos to sustainably obtain or even grow native PNG browse species for their animals’ food, the analysis of primary nutrient and mineral composition of wild diets could be used to determine suitable substitutes or alternate food sources.

Mr. Smith further highlighted the importance of further research into the behaviors and feeding habits of tree kangaroos in the wild to better understand them and inform their proper care in captivity.

In addition to this nutrition study, the TKSSP also developed a “Body Scoring Chart” to assess overall animal body conditions, and the tracking of age and developmental milestones of joeys or young tree kangaroos in captivity- both vital tools currently used by the TKCP field team to study the marsupials in the wild.

Regarding the overall protection and saving of such endangered animals, the TKSSP recommends a holistic approach.

“When it comes to the Matschie’s tree kangaroo, collaborations between PNG conservation programs, the TKCP, local communities and outside programs such as the TKSSP will help to elevate awareness and provide support to protect this beautiful species and the habitat in which they live”, Ms. Blessington said.

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For more information, visit the Tree Kangaroo Conservation Program (TKCP) website and learn about its amazing work in the Cloud Forests of the Huon Peninsula in Morobe: https://www.zoo.org/tkcp

You can also visit the Tree Kangaroo Alliance (TCA) website to learn about their conservation work in the Torricelli Mountains of East Sepik: https://www.tenkile.com/

If in Port Moresby, call into the Port Moresby Nature Park to witness and learn more about these remarkable animals: https://www.portmoresbynjaturepark.org/