Carnaby’s food of choice: non-native pines

Carnaby cockatoos utilise non-native pines. Image by lostandcoldENDANGERED Carnaby’s cockatoos (Calyptorhynchus latirostris) are using pine trees as fast food—and have been since the 1940s.

But plans to harvest Perth’s pine plantations, without any re-planting, will remove the food source by 2031 or earlier, further putting the species at risk.

A new paper by Professor Will Stock from Edith Cowan University’s Centre for Ecosystem Management looks at the ecological association between Carnaby’s cockatoos and pine using behavioural, nutritional and phenological data.

It has calculated that the Gnangara pine plantations could sustain 3,000 birds for six months of the year.

“Pine plantations provided high densities of seed over a large area and Carnaby’s cockatoos fed throughout these plantations and removed almost the entire annual crop of pine cones,” he says.

“Pine seed has energy and protein contents equivalent to native food sources and, critically, is available in summer when breeding pairs have young offspring to feed.”

The chemical compositions of the seeds from the native and non-native plants eaten by cockatoos were typical of nuts, in terms of energy available per unit of mass, with the pines about 27 per cent higher in energy than the native species.

Differences among species, in seed size and ratio of cotyledon mass to seed testa, leads to a 16-fold difference in the number of seeds of each species required to meet the birds’ daily minimum field metabolic requirements.

While pines are an introduced species, their removal—and subsequent effect on the cockatoo population—would not bring the natural environment back into balance.

“Too much land has been cleared so there is no ‘natural balance’ possible without extensive revegetation of already transformed landscapes,” Prof Stock says.

“The Gnangara pine [mostly maritime pine Pinus pinaster] plantations are the largest in the Perth region and, at their historical maximum in 2002, covered an area of 23,000ha. Since 2004, they have been harvested without replacement.

“The Gnangara Sustainability Strategy proposed revegetating portions with native vegetation but the State Government has yet to implement any revegetation activities more than three years after the draft strategy was released.”

Professor Stock says a range of species could be planted to replace pine as a food source. He also highlighted a short-term solution.

“A recent article showed the difficulty a macadamia and pecan nut grower was having with Carnaby’s,” he says.

“This is not surprising, considering the loss of food from the pines, so the birds are switching to whatever is available in the landscape.”