The birds perished during extreme weather conditions on Wednesday January 6, when temperatures reached 47 degrees in the Hopetoun area with strong, hot northerly winds, while temperatures of 50 to 53 degrees were reported by landowners in Munglinup.

At least 115 dead Carnaby’s black cockatoos were found at the Everett Country Club in Hopetoun.

A further 37 cockatoos, six regent parrots, two galahs, three mudlarks, three ravens, four yellow throated miners and one kestrel were reported at Munglinup.

DEC senior wildlife officer Kevin Morrison said laboratory tests had not revealed any obvious cause of death.

“The Department of Agriculture and Food’s Animal Health Laboratories conducted examinations and tested samples for infection and a range of diseases such as avian influenza. These results were negative,” he said.

“The examinations of tissues found no significant changes, although this process was hampered by the degree of decomposition that had already occurred due to the extreme weather conditions.

Mr Morrison said tests conducted by the Chemistry Centre on tissue samples from the dead birds have so far ruled out pesticides and chemicals including organophosphates, organochlorines and heavy metals as possible causes of death.

“The process of ruling out possible causes enables us to narrow down what may have killed the birds, as there is no definitive test that can be done to establish whether heat stress was the actual cause,” he said.

“Therefore the cause of the bird deaths remains inconclusive.”

Mr Morrison said a similar bird death incident occurred in February 2007 between Yealering and Cunderdin when more than 200 ringneck parrots are believed to have died of heat stress caused by 45-degree temperatures and strong winds.