by Vultures, hyenas and Tasmanian devils are highly efficient scavengers, capable of quickly locating and consuming carrion, including meat and bones.
When we think of scavengers, these large carnivores come to mind – not brushtail possums.
So it came as a surprise when these Australian marsupials turned out to be one of the most common scavengers we caught on camera in our new study published online this month wildlife research.
circle of life
No Australian vertebrates survive solely on scavengers – for our wildlife, carcasses are ‘sometimes food’.
Scavengers play an important role as ecosystem cleaners, helping to remove carcasses from our landscapes by eating them.
With this in mind, we wanted to know how different seasons affect the use of carcasses by vertebrate scavengers in Kosciuszko National Park in south-east NSW in the Australian Alps.
Winter in the Australian Alps blankets much of the landscape in snow. But by the following summer, the same landscape can warm significantly and even experience intense bushfires.
We found that the cleanup was very seasonal when it came to who visited the carcasses over the course of a year. Surprisingly, bush possums and ravens drove these seasonal trends, as recorded by the most common scavengers, with possums feeding primarily in winter and ravens in spring.
These results emphasized the key role played by smaller scavenger species and revealed new insights into the feeding habits of the bush-tailed possum, which is widely believed to feed primarily on plants and insects.
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Catching possums in the act
We expected different scavengers to emerge each season, so our monitoring ran for a full year from March 2020 to March 2021.
In each consecutive season (starting in autumn, then winter, spring and summer) we placed 15 fresh eastern gray kangaroo carcasses – from local culls – throughout the alpine environment (60 carcasses in total).
Each of these carcasses was monitored by a remote-controlled camera for 60 days to record any species that visited it, whether to examine the carcass or to feed on it.
In 745,599 remote camera images, the scavenger species we recorded were spotted quolls, wild cats, dingoes, pintos, wedge-tailed eagles, bush possums, ravens, red foxes, and wild boar.
88 percent of the scavengers we recorded were carried out by bush possums and ravens.
Survive the seasons
We expected that the time it would take for the scavengers to find a carcass—and then eat it—would be associated with the carcass’ smell.
In the summer, we figured that the heat would make the carcass smells more pungent and therefore easier to find.
We were wrong, not about the smell, but about how quickly vertebrate scavengers would find the carcasses.
It actually took longer for the summertime vertebrate scavengers to find the carcasses, whether for study or scavengers. Carcass visits peaked in winter.
But we have a possible explanation for this.
In summer, a carcass becomes colonized by many scavenging insects within minutes of its death. These “mini-scavengers” may have accelerated carcass decomposition so much that vertebrate scavengers had little time to find the fresh carcasses.
Feeding rates may also have been lowest in summer because other food sources were plentiful.
Bush possums, for example, feed primarily on leaves, flowers, fruits, and insects, most of which are only seasonally available in the summer.
In winter, when these food sources are scarce, bush possums accounted for 81 percent of all recorded scavengers. They ate carrion three times more often than in the summer.
nutrition of the family
We also considered that scavenger breeding seasons could have an impact on their scavenging rates and behavior.
Ravens breed from late winter to early spring, prioritizing nest building first.
This was even caught by our remote controlled cameras, where ravens were observed collecting fur from the kangaroo carcasses, presumably for nest building.
After nest building, chick rearing often requires breeding pairs to divide time between foraging, chick feeding, and nest protection.
Ravens naturally need more energy during this time and need to supplement their diet with plenty of high-energy foods such as carrion.
Of all the raven hunts we recorded, 67 percent were conducted in the spring. This suggests that ravens rely heavily on carrion during their breeding season to supplement their own diet – and that of their chicks.
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Where were the usual suspects?
It was also clear that the larger species (dingoes, wedge-tailed eagles, wild boar) were rarely recorded at the carcass sites. The low scavenging rates of these larger animals could be another reason why the smaller scavengers were so common.
This is because larger scavengers can scare away or prey on smaller scavengers, potentially removing them from carcasses. Larger scavengers also have larger appetites, so in their absence there may have been more carrion to be found for smaller species.
While we don’t have a good estimate of the true density of larger scavengers in the area, species like the dingo are under scrutiny in the wider region, potentially limiting their numbers.
Beyond the mountains
Given the scale of culling operations in Australia targeting overabundant native species (like kangaroos) or pests like deer and horses, not to mention all the road deaths, it’s important to understand what happens to carcasses in the landscape.
Our study established a baseline for scavenger dynamics in an alpine ecosystem, and our methods could be used to learn more about scavenger ecology in many different settings.
In this case, it was (surprisingly) bush possums that apparently used carcasses as a food source in the Australian Alps.
James Vandersteen, PhD Student, UNSW Sydney and Thomas Newsome, Senior Lecturer, University of Sydney.
This article was republished by The Conversation under a Creative Commons license. Read the original article.
