If you thought koalas were just quiet, sleepy, eucalypt-chewing bundles of cuteness, think again.
These Aussie icons turn supersonic during mating season.
Normally they spend most of the day and night sleeping.
But now, during the mating period at night, they bellow very loudly.
Australian and Austrian scientists have found the bellows are used by male koalas as a way to boast about their body size and make them sound “even larger than bison”.
The research, published in The Journal of Experimental Biology last week, found that the low, rasping bellows are the result of a “descended larynx”, something previously thought to be a human-only feature.
A “descended larynx” occurs when an animal’s voicebox sits very low in its throat, allowing it to form a range of sounds. In humans, it is used in the formation of speech. In animals, such as koalas, it is believed to be used to distinguish between a male and female.
The bellows – used to attract females and intimidate male rivals – are made deep in the night, said Dr Bill Ellis of the University of Queensland, who participated in the study.
“What we found is that most bellowing happens around midnight. Deep in the night is when they are most active.
“We see them sitting and sleeping when we walk past them [in the day]. But when we’re asleep in the middle of the night, quite often they are very active and moving quite large distances between trees – up to a kilometre a night.”
Female koalas also tend to mate with different males each year, suggesting the bellows could be an individual signature – like a voice print – that the marsupials use to identify one another, he said.
Residents at Hawks Nest, on the northern shore of Port Stephens, are all too familiar with the noises.
“I’ve heard of people annoyed about the bellowing – it does keep them awake at night,” said Ian Morphett, a Hawks Nest koala rescuer, adding that the male and female koalas with last year’s babies had been seen in town at the start of the breeding season.
“We had an English tourist at the caravan park and a male koala started bellowing in a gum tree outside the cabin she was staying.
“She thought it was a lion – it was that loud … She rang up the caravan park manager and said, ‘Please help me, save me!”‘
Mr Morphett said the upside was that residents would not be disturbed for long as koalas moved to a different area almost every day in search of fresh leaves on trees.
“They are only irritating for a short period,” he said, adding that the bellowing did not last through the night either.
“They bellow for maybe half-an-hour, then shut up for a while, then have another go a few hours later. I don’t think there’s 12 hours of bellowing.”
Dr Ellis said he hoped to find out how far the bellows travel and whether the calls are affected by other sounds in the forests.
Koala breeding facts:
Breeding season: October to November.
Female koalas tend to mate with a different male each year.
Gestation period: 35 days.
Joeys stay inside mother’s pouch for six months.
They are out of mother’s pouch after one year.
NSW Government Office of Environment and Heritage’s factsheet