South Australia's Department for Environment and Water is celebrating 40 years of its annual kangaroo aerial survey.
The survey started in 1978 and for four decades has tracked the kangaroo population in areas including Port Augusta, Coober Pedy, Lake Torrens and the Flinders and Gawler Ranges.
DEW Management Operations Manager Tom Gerschwitz has been involved in the aerial survey program for more than 20 years.
"It is certainly a very interesting job, you see all sorts of strange and interesting things and lots of little things stick in your memory," Mr Gerschwitz said.
"I can recall seeing a kangaroo lying flat on its back with its legs in the air, and it sort of rolled over and followed us as we were passing over and was watching what we were doing."
Forty years of counting
Mr Gerschwitz said there has been a range of different trends in the population since he has started.
"Numbers were high in the mid-1990s, and they fell away with the poorer conditions, then remained at a fairly stable level for a while," he said.
"Since about 2013 the numbers have been increasing.
"From our survey last year we've got just over 5 million kangaroos across the commercial harvest area."
Mr Gerschwitz said it is important for the department to have an understanding of the trends in kangaroo populations, and that the survey enables landholders to better manage the problems 'roos can cause.
"It's a typical boom or bust species — the numbers increase following a number of good years and may well drop back when the conditions start drying out," he said.
"The data will also help inform the setting of sustainable quotas within the commercial harvest area for kangaroos, and helps us understand the effect of environmental conditions on 'roo numbers," he said.
"They do cause a lot of grazing pressure so if we can get an idea of the numbers we can help pastoralists with management on their properties.
Observing from the sky
An average day of counting involves two observers in a Cessna 206 who scan the landscape and count kangaroos in a 200-metre-wide strip each side of the aircraft, surveying one square kilometre every 97 seconds.
Mr Gerschwitz said it is important not only to have good observation skills, but also a cast iron stomach.
"We are flying at a low level, about 76 metres off the ground and we fly east-west transects across the state at a speed of 100 knots," he said.
The survey runs for a total of three weeks every year, during which time the crew takes to the skies for several hours in the morning, has a break, and then caps off the day with another few hours of observation in the afternoon.
During those times, the observers do not solely count kangaroos.
"Kangaroos are obviously our priority," Mr Gerschwitz said.
"But we can count emus and feral animals like goats, camels and donkeys.
"We count the different species of kangaroo and we remember the information and count in our head and then at the end of the 97 seconds we record what we have seen."