Carnaby’s carnage laid bare in ongoing fallout from WA’s horror summer

The ongoing costs of Western Australia’s hottest ever summer in 2023-2024, immediately followed by Perth’s eighth-driest ever autumn, are laid bare in a new report on a population of Carnaby’s black cockatoos.

CSIRO Publishing has released new research identifying how feral cats can pose a “significant threat”, revealing details further to WAtoday’s March report on how catastrophic conditions led to black cockatoo “carnage”.

Black cockatoos are in dire straits across WA.Credit: Rick Dawson / Dean Arthurell

The study published Monday in Pacific Conservation Biology was done at the site the March story concerned: Coomallo Creek, a nine-kilometre belt of wandoo woodland, farmland and remnant heathland in the central northern Wheatbelt, not only prime black cockatoo breeding territory but also abundant and diverse habitat for feral cats and their typical prey.

Until, that is, the black cockatoo breeding season of October 2023-May 2024 saw only 60 millimetres of rain – less than one-third of the period’s long-term average – and WA’s hottest-ever summer with 57 days reaching over 35C, 14 of them over 40C.

The drought appeared to decimate house mice numbers at Coomallo Creek, which in 2021 and 2022 had also supported large populations of boobook and barn owls, the report says, and rabbit populations also fell to near zero.

During lean times, cats expand the species of prey targeted; and with the mice and rabbits gone, the report says, the only alternative was birds: Port Lincoln ringnecks, galahs, western corellas – and Carnaby’s black cockatoos.

Feral cats have preyed on nesting Carnaby’s females, their nestlings and eggs in three of the 38 years this breeding site has been studied: in 2014, 2023 and 2024.

Each predation event got more severe in terms of mortality, until following the intense eight-month drought of 2024, cats wiped out almost a quarter of a breeding attempt total already way lower than normal after the drought also caused an unprecedented food shortage for the birds themselves.

There was another mark of escalation in 2024, and this gets grisly – but report authors noted its potential significance.

Feral cats often kill significantly more than they eat, the accepted scientific wisdom goes, and the predation events of 2014 and 2023 did not provide any evidence contrary to this typical behaviour.

But in 2024, the cats took everything they could possibly digest, including going to lengths to consume the breeding mothers’ brain tissue, leaving only bones, eggshells, and flight and tail feathers.

L-R: Triple One, a breeding mother known for her skill at rearing chicks successfully, disappeared during the 2024 predation event; The hoped-for sight; The remains found instead. Credit: Rick Dawson

The authors say this further supports the notion the cats were struggling to find food.

“Feral cats may not be regular predators of species such as Carnaby’s cockatoos, but that when they do prey on this species, the effect can potentially be devastating, especially in years in which weather conditions cause low and delayed breeding,” they wrote.

“Their capacity to catch and subdue adult females while they are incubating eggs or brooding nestlings poses a serious threat to the conservation of the species, as increased adult mortality has previously been identified as a key threat.”

Rick Dawson, one of the authors, told this masthead the loss of Carnaby’s life was “probably double” the official recording, given the limited number of hollows that could be monitored.

“This is devastating for the species,” he said.

“Cats only need to learn once how it easy it is … they’re bloody good predators.

“We need to keep control of them, and the landowners are behind us.”

The landowners across three rural properties have, in collaboration with the authors, now culled nine feral cats over 24 months and feel cautiously optimistic they have safeguarded this year’s cockatoo families.

But they stress the government’s updated black cockatoo recovery plan update currently being drafted must plan for droughts, when cats could again represent “a serious threat”.

They conclude combined targeted trapping and shooting programs, possibly with metal guards around trees with nesting hollows, may mitigate this threat.

“It’s been reported to the black cockatoo recovery team at [The Department of Biodiversity Conservation and Attractions], so they are well and truly aware of this,” Dawson said.

“I’ve got nothing against cats, but to lose six breeding females? We will never get those back. Nestling survival rates are low and if you lose some it’s not the end of the world, but when they took those six adult females it was very sobering.

“We had been monitoring them for years, and they get better at it past their first few years, when they reach 15 or 20 years old.

“We encourage farmers to humanely control cats on their properties. These cats are just doing what they do, and this endangered species needs every bit of help it can get.”

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