Getting down with the rat-kangaroo

On a rainy day in North Queensland, Australia, we found ourselves tromping through the rainforest of the Wet Tropics, searching for the elusive musky rat-kangaroo. The Wet Tropics bioregion is home to a staggeringly high rate of biodiversity and endemic species, including the musky rat-kangaroo.

This small diurnal (day-active) marsupial can be seen hopping through the leaves in a way akin to that of its evolutionary descendants, the kangaroos. At about the size of a rabbit, the musky rat-kangaroo is easily missed; its dark brown coat, small eyes and scaly tail allow it to blend into the deep rainforest underbrush. The secretive mammal lives on the forest floor, building its nests in the buttresses of trees and feeding on native fruits. Between picking terrestrial leeches off of our legs and listening to the startling crack of the eastern whipbird’s call, we circled lakes Eacham and Barrine, pausing to observe the half-eaten fruits littering the rainforest trails — evidence of the musky rat-kangaroo — as we tried to assess its population size.

During this spring’s wet season survey, our fellow SIT study abroad students were spread across four different locations, each a known musky rat-kangaroo habitat, counting the number of individuals present. The results from these transects would be the third data set in a series of surveys at these sites, the first two occurring in March during the wet season and October during the dry season in 2014.

With this third survey, we have begun to uncover a little more about the patterns of the local musky rat-kangaroo population. No similar surveys have been conducted on this species, so our results from this wet season have begun to build a picture of the year-round cycles of this population. At our lake sites, we saw nearly six times as many musky rat-kangaroos as at the other two sites: Gadgarra National Park and a section of continuous forest in the Gillies Range. Our data highlight that lake habitats may be more suitable for the musky rat-kangaroo, a species which generally tends to prefer wetter areas.

A year earlier, in the 2014 wet season, both lake sites again had more individuals than Gadgarra and the Gillies Range. There was, however, a noticeable population decline at both Barrine and Eacham this year compared to last. This unpredicted decline could be a result of population cycles over multiple years or increasing visitation and recreational use of the popular lake sites.

With this most recent study, we have really begun to understand the annual population cycles associated with breeding and birthing seasons. In the survey preceding ours (October 2014), there was a large increase at all four sites in the population size. At first glance, this upward trend may seem to contradict the population decline between the 2014 and 2015 wet season surveys.

However, a closer look at the life cycle of the musky rat-kangaroo may explain this change; musky-rat kangaroo breeding season is typically February to July, during our wet season surveys. Thus, perhaps the observed smaller population size in the wet seasons may have been because fewer young juveniles were present in the forest compared to during the dry season, post-birthing period.

As Wet Tropics visitation continues to rise, especially at lakes Barrine and Eacham, it is imperative that we work to protect the musky rat-kangaroo’s habitat and population. If nothing else, there is an obvious need to continue such surveys in order to gauge the status of the population, as the more information we have, the better we can work to preserve this unique marsupial and the whole of the Wet Tropics.