Many native bats are smaller than the palm of your hand, but they can eat more than their body weight in insects each night, making them an important ally for integrated pest management on cotton farms.
Research using a combination of dietary studies, acoustic and other data has estimated the direct value of insectivorous bats to the Australian cotton industry at $63 million a year.
Since then a team of researchers has developed a solar-powered automatic recorder equipped with artificial intelligence to identify sounds from birds and bats in a cotton field and transmit that information to a website.
World-renowned zoologist Professor Stuart Parsons, who is Dean of the University of the Sunshine Coast's School of Science, Technology and Engineering, said the system would allow growers with sensors on their farm to monitor those species of birds and bats on their properties.
"It was a proof of concept," he said.
"We created the website, we put out the sensor, we tested the artificial intelligence, and it essentially shows that you can track these birds and bats through the cotton growing season, to see how the numbers change."
Prof Parsons, who led the project, said many of the farmers involved during the first phase of collecting and ground truthing a library of bird and bat calls in remnant vegetation and cotton fields around Narrabri, Wee Waa, Moree, St George, Dalby and Miles were "dead keen" on encouraging biodiversity, especially once they learned which species fed predominantly on cotton pests, such as bollworm.
They often knew which birds frequented their farms but were much less aware of the insect-eating bats, largely because most make ultrasonic sounds that can't be heard by the human ear, and many feed at dusk and during the night.
"They're generally quite small," he said.
"They can vary from seven grams to a little bit more than 20 grams, with a 30 centimetre wingspan, and most people won't see them.
"Unless you look at the wing shape they can sometimes be quite hard to tell apart, particularly at a distance, from birds like swallows and swifts.
"They've got this really jagging flight, and they overlap for a few minutes with the swallows and swifts who go away and then the bats come out."
Prof Parsons said the insect-eating bats were dependent on woodland for refuge from predators, food and roosting when they weren't darting into crops to feed on insects, but many weren't able to migrate to isolated patches of bush or shelterbelts.
"They need to follow wooded or treed areas in what we call landscape connectivity, which is really important for the bats and some of the birds that we've looked at," he said.
"The next question that we're going to answer is we're going to look at how a connected landscape benefits farmers.
"We're going to use the acoustic sensors to bring together integrated pest management strategies the farmers are using, the connectivity of the landscape, and which birds and bats are actually in those areas."
After building another 11 sensors, Prof Parsons said they would survey farmers about their IPM strategies and use remote sensing data commissioned by the Cotton Research and Development Corporation from 2rog Consulting to identify habitat in cotton growing areas with good and poor landscape connectivity.
The team, which includes Queensland University of Technology professors Paul Roe and Susan Fuller as lead investigators, would then deploy the sensors to monitor the abundance of insectivorous bats and birds in crops during the cotton growing season.
Prof Parsons said past research had shown greater diversity in many animal species, whether they walked or flew, in areas that were part of a connected landscape, with corridors of vegetation linking habitats.
"A lot of animals use linear features to navigate and find their way," he said.
"The way echolocation works, a bat needs to be connected to something, so it knows where it is in the pitch black.
"It does that by echolocation off the ground, but also off things like trees, canals and rivers.
"Some of the ones that we're looking at, they're fairly slow fliers, and they're not strong fliers so it makes them quite vulnerable if they fly out over an open area to be picked off by a predator.
"If you fly along next to a hedgerow or tree line, you can duck into it, and it makes it harder for the predator to get you.
"So there's lots of reasons why that connectivity helps. But I would think we're going to see greater diversity in connected landscapes, and therefore greater benefit to the growers."
Ecologist Dr Heidi Kolkert estimated a population of bats could remove 77-119 tonnes of moths from cotton crops during the growing season, equating to a direct benefit of $99-$126/ha in dryland cotton and $286-$361/ha in irrigated crops.
The benefit stemmed from better yields and lint quality by preventing insect damage and the spread of disease, as well as savings on insecticide application.
But because different bat species selectively targeted different insect pests, conserving and encouraging diversity in non-crop habitat was essential to support a variety of different bat species foraging over crops, Dr Kolkert wrote in a paper on the subject.
Cotton growers in the Narrabri and Wee Waa areas who are interested in being involved in the CRDC-funded research can contact Prof Parsons at sparsons3@usc.edu.au.
