The population of rare Cape Barren Geese in South Australia has plunged over the past 20 years, based on the results of an aerial survey.
The survey, the first since 2001, was conducted over the lower Eyre Peninsula, the lower lakes, and across Kangaroo Island.
It estimated the number of geese at about 7850 birds, a roughly 30 per cent fall on previous estimates of approximately 11,270.
Environment department ecologist Karl Hillyard said despite the fall, the size of the flock was still much higher than the 500 thought alive in the 1950s when the species was first listed as protected.
"Changes in agricultural practices are thought to have played a significant role in the reduced numbers over the past 20 years," he said.
"Land irrigated for grazing dairy cattle around the lower lakes has historically been favoured feeding grounds for geese.
"However, with the decline of dairying in that area, there has been a significant decrease of irrigated pasture."
Dr Hillyard said it was unclear how the Kangaroo Island bushfires in early 2020 had impacted the species overall, with numbers slightly increasing on the island.
However, 70 per cent of the birds were spotted on the largely unburnt eastern parts, with only small numbers present in the bushfire-affected areas to the west.
The department will conduct another state-wide aerial survey during February next year, and a ground survey of the breeding islands in June to closely monitor the geese population and gather more information on what might have caused the observed reduction in numbers.
Australian Associated Press