Photo: A female bentwing bat with her pup amongst a colony of young ones. (Supplied: Steve Bourne)
Updated
During scorching summer weather there is no better place to be than underground - especially if you are a pregnant microbat.
Each summer tens of thousands of female eastern bentwing bats migrate to limestone caves in southern New South Wales to deliver and rear their pups.
There are only three known 'maternity' caves in NSW suitable for the roosting of large colonies of the vulnerable species and females will migrate up to 300 kilometres to roost there.
"They only give birth to one young a year and the mortality rate is quite high," said Doug Mills of the NSW National Parks and Wildlife Service.
"The fact that there are only three maternity sites is a really significant conservation issue."
One of those caves is at Wee Jasper, north-west of Canberra, where researchers are using some unusual technology to monitor bat colonies.
Thermal video cameras record the flurry of night feeding by the matchbox-sized mammals.
Dr Mills then uses software adapted from the United States Army to trace and count individual bat flight paths.
"It enables us to count accurately and we can track if there's any changes in the population," Dr Mills said.
Five years of monitoring has revealed the population is recovering after years of drought.
Dr Mills says they first counted about 17,000 bats and that has increased by 5 to 10 per cent each year.
"We are looking at somewhere in the vicinity of 2,000 more bats each year over the last two years," he said.
"Twenty thousand is the current estimate of female bats congregating at a single location to give birth and raise their young."
Those 20,000 lactating female bats will feast on a whopping 300 kilograms of insects each night for up to four months.
"The fact they have recovered on the back of what appears to be the drought breaking is really good news," Dr Mills said.
Dr Mills's 'big brother for bats' approach is now being used by South Australian researchers and there is interest from those in Queensland.
Wee Jasper wool grower Ian Cathles helps Dr Mills monitor the vulnerable species.
"In the past counting the population was extremely difficult," he said.
"You either had to do it standing there trying to count in twos, fives and ones. It was a fairly haphazardous count."
Mr Cathles says the new tracking system is phenomenal.
"Basically you are looking at missile tracking technology that homes in on a missile and tracks it flying at high speed," he said.
Mr Cathles had lived in the area for 40 years before he found out about the maternal bat breeding caves.
"It was just astonishing to see the whole roof of the cave was like a brown or beige-coloured velour of tens of thousands of bats," he said.
And the burgeoning microbat community does not worry Wee Jasper's human residents.
"We get these big influxes of population over short periods of time but the rest of the year it is just 65 of us!" Mr Cathles said.
