Upon flicking through and sorting hundreds of photos from fauna cameras recently deployed on a Land for Wildlife / Voluntary Conservation Agreement (VCA) property at Weyba Downs, I noticed a curious behaviour exhibited by Eastern Grey Kangaroos (Macropus giganteus).
I had cameras set up facing hollows at the base of two old Scribbly Gums (Eucalyptus racemosa) at different locations on the property. Scattered among the pictures of Echidnas, Koalas, Lace Monitors, a Red-bellied Black Snake, Yellow-footed Antechinus and Common Brushtail Possums were pictures of Eastern Grey Kangaroos repeating the same behaviour. They were meticulously investigating the insides of hollow trees; the juveniles would even completely disappear into the hollows for short periods!
A joey goes inside the hollow whilst Mum supervises.
Eastern Grey Kangaroos eat a diet of up to 98% grass, but with no grass (or any plant for that matter) inside the hollows, I was at a bit of a loss as to what they were doing. Wallabies are known to consume a wide range of underground-fruiting fungi, and rotting ground hollows such as the ones being photographed would be a prime location for many fungal species. However, unlike wallabies, mycophagy (fungus- eating) has not been extensively reported in Eastern Grey Kangaroos.
Studies have shown that scent marking is important for indicating social status in Eastern Grey Kangaroos and may also be important for predator recognition. However our in-office wildlife expert, Nick Clancy, thought that the Eastern Grey Kangaroos were demonstrating too much interest in the hollows for scent marking.
A joey ventures into the hollow on its own.
A large male Eastern Grey Kangaroo tries to squeeze his way into the hollow.
I sent the series of photos to the Queensland Museum and some local ecologists for further analysis. A few weeks later, I was delighted to receive a reply from behavioural ecologist Associate Professor Anne Goldizen from the University of Queensland. Anne suggested that the kangaroos were obtaining salt or some other desired mineral by eating the soil.
Around the world, geophagy (consumption of soil) is widely observed and studied in herbivorous mammal species. Until recently, geophagy had never been reported in any marsupial species. In 2013, Emily Best along with Anne Goldizen and Julia Joseph published the first report of Eastern Grey Kangaroos using natural salt licks at Sundown National Park to supplement their salt and mineral requirements. The researchers found that visitations by kangaroos to salt licks increased depending on their reproductive state. Lactating females and large males spent the most time at the lick. To date, this behaviour has not been detected in any other intensively studied kangaroo population across Australia.
Now, I know what you’re thinking, “Why would the soil inside a hollowed out tree have more salt or minerals than any other patch of dirt?”
Kieran Aland from the Queensland Museum offered an answer:
“Rain-protected soil containing ash in the base of a tree hollow would certainly retain a higher concentration of soluble elements than surrounding rain-washed soil outside of the hollow.”
Other suggestions received were that the kangaroos were seeking trace elements in the ash at the base of the hollow, or that the roos were eating mineralised clay/ termite nesting material within the hollow.
Armed with a fascinating hypothesis, I will be back out to Weyba Downs with my fauna cameras to try and capture video footage from inside the hollows to confirm what this behaviour is all about. I just hope the resident Red-bellied Black Snake doesn’t get too upset with me!
References & Further Reading
Best EC, Joseph J & Goldizen AW (2013) Facultative geophagy at natural licks in an Australian marsupial. Journal of Mammalogy, 94(6) 1237-1247.
Claridge AW, Trappe JM & Claridge DL (2002) Mycophagy by the swamp wallaby (Wallabia bicolour). Wildlife Research, 28(6) 643-645.
Jackson S & Vernes K (2010) Kangaroo: A portrait of an Extraordinary Marsupial. Allen & Unwin.
Ramp D, Russell BG & Croft DB (2005) Predator scent induces differing responses in two sympatric marcopodids. Australian Journal of Zoology, 53(2) 73-78.
Salamon M, Davies NW & Stoddart M (1999) Olfactory Communication in Australian Marsupials with Particular Reference to Brushtail Possum, Koala and Eastern Grey Kangaroo. In: Advances in Chemical Signals in Vertebrates (Eds. Johnston et. al.), Springer.
Taylor RJ (1983) The diet of the eastern grey kangaroo and wallaroo in areas of improved and native pasture in the New England Tablelands. Australian Wildlife Research, 10(2) 203-211.
Article by Danielle Crawford Land for Wildlife Officer Sunshine Coast Council