Walking through a constant downpour between fallen trees, leaves and vines, our search for a small brown marsupial about the size of a rabbit continues. Scurrying through the lush green understory of the Australian Wet Tropics rainforests, one can spot the smallest of the kangaroos. A remnant of an earlier age, the musky rat-kangaroo has persevered through evolutionary changes as well as environmental ones. In the face of climate change and habitat loss, this resilient little marsupial may face its biggest challenge yet: humans. Although it is not the first keystone species that comes to mind for most people, this little rainforest gardener plays a much larger role than its size suggests.
While studying abroad in Australia, SIT (School for International Training) students don’t spend much time in a classroom. Instead we go out into the rainforest and search for critters like musky rat-kangaroos, affectionately known as hypsies for their scientific name, Hypsiprymnodon moschatus. Class at SIT this week involved a study focused on the musky rat-kangaroo through field observation. In our study we aimed to assess changes in populations of musky rat-kangaroos between the wet and dry seasons and between fragmented and continuous habitats.
Peering through the dense understory, we were lucky enough to spot nine hypsies in our transect at Lake Barrine, the most that were spotted for this season’s data collection. One was so close to us that we almost tripped over it while looking the other way!
Sampling occurred at four different sites known to support musky rat-kangaroos, including two habitat remnants (Lake Barrine and Lake Eacham) and two continuous areas of rainforest (Gadgarra National Park and Gillies Range). Two sampling periods (morning and afternoon) lasting for two hours each were conducted along man-made paths to account for different behaviors throughout the day. We surveyed musky rat-kangaroo populations by recording all sightings and behaviors, like eating seeds or fruits. Finally, we compared our data to those collected in the past two semesters (one wet and one dry season) by previous SIT students.
Musky rat-kangaroos come in small packages of only 1.5 pounds and their bald, scaly feet and prehensile tail suggest that they evolved long ago from a possum-like ancestor. Their distribution is limited to the Wet Tropics rainforests of northeast Australia, and they particularly like cool, wet areas near streams and lakes. In the rainforest they have a simple but vital role: to eat, bury and disperse seeds and fruits.
In Andrew Dennis’ 1997 study of musky rat-kangaroos, he found that they inadvertently become gardeners of the rainforest, planting and dispersing large seeds that would not otherwise grow. These tiny, rat-like kangaroos are active during the day and can be found at night sleeping in small nests that they create using dried leaves and ferns, which are usually located between tree buttresses, rock piles or prickly Lawyer vines.
Hypothetically, hypsi sightings are expected to be higher during the dry season because after the breeding season (February-July) has ended, new babies will begin to emerge from their mothers’ pouches and join the surveyable population. Looking at the compiled data, a total of 21 musky rat-kangaroos were observed during this wet season and 48 were observed last wet season (March 2014), in comparison to the total of 82 musky rat-kangaroos observed in the past dry season (October 2014). This leads us to believe that our hypothesis is correct, but we are still concerned about the difference in numbers between this wet season and the last.
A possible explanation for this can be found in musky rat-kangaroo expert Andrew Dennis’ 1997 research. He found that hypsi reproduction fluctuates depending on the availability of fruits in a given year. One possibility is that changing climatic patterns are affecting the timing of fruiting plants, and thus the hypsi breeding season. For example, the wet season this year has yet to start. This could have rippling effects on all of the fruiting rainforest species that depend on these heavy rains.
Furthermore, we expected to find more hypsies in the continuous rainforest site than in the remnant because they are known for their inability to survive in forest fragments. A possible theory explaining why more hypsies were found in the fragments than in the continuous forests is that those sampling sites were both next to lakes, whereas the continuous forest tracts did not contain such large, stable bodies of water. Andrew Dennis also found that hypsies prefer living near stable water sources that provide ample resources for denser vegetation and fruiting plants, so this makes sense, especially if population sizes and breeding numbers are controlled by food availability.
Overall, this study taught us a great deal about field observation methods, but it also presented some potential future concerns for the musky rat-kangaroo and, more importantly, for the Wet Tropics as a whole. We also learned to appreciate the joys of field-based learning, which is much more hands-on than sitting in a lecture hall. Better yet, we got to experience the luxury of terrestrial leeches on our eyebrows, ankles and toes while searching for fluffy brown rat-kangaroos in the rainforest. More research is needed on the subject of hypsi populations, but for the time being, our 99 problems do not include the loss of the musky rat-kangaroo.