Carnaby’s offspring bank on rainfall

Over 50 years ago, there were probably hundreds of thousands in the area and now we are looking at an estimated 40,000 left in the south west, Dr Mawson says. Image by Sandra L ChungAN endangered species of cockatoo native to South West Australia may have a brighter future as a long-term study has revealed a strong link between rainfall and the bird’s breeding patterns.

Perth Zoo director of Animal Health and Research Dr Peter Mawson says birds use environmental cues to time their breeding to maximise their chances of raising young when food is most abundant, including photoperiod, temperature and rainfall.

“Rainfall cues Carnaby’s Cockatoo to leave the coast and fly inland to breed - in fact, we found a 60 per cent correlation between the timing of the onset of autumn rains and the start of breeding in spring,” Dr Mawson says.

“Our climate is becoming drier and sometimes there is no rain until late June, so there is no cue for the birds to go home and breed.”

Chicks spend 10 to 11 weeks in the nest, so when temperatures rise above 35 degrees Celsius, which happens in late breeding seasons, it becomes hot in the nest and too hot for parents to forage for food.

Either way, the chicks are at greater risk of dying from dehydration or starvation.

The study is based on research ornithologist and conservationist Dr Denis Saunders began in 1969 in the northern Wheatbelt.

Dr Mawson says they weighed, measured and put leg bands on nestlings to establish an index of health relative to their age.

“Not surprisingly, the chicks (who) hatched later in the breeding season don’t do as well,” he says.

“If our climate continues to dry, it may reach a point where the cockatoos can’t raise enough chicks to sustain the population.”

By the 1980s, Carnaby’s Cockatoos’ numbers had declined due to vegetation clearing for the development of agriculture.

In 1999, the species was officially recognised by the Australian Government as endangered.

“Over 50 years ago, there were probably hundreds of thousands in the area and now we are looking at an estimated 40,000 left in the south west,” Dr Mawson says.

“The scale and rate of decline is quite frightening.”

“This research will help confirm or deny the cockatoo’s path to extinction and provide hard evidence for government to change legislation to persuade people to keep the trees they nest in, especially in areas close to the coast that receive early and higher rainfall.”