Australasian Science: Australia's authority on science since 1938

Burning Questions for Black Cockatoos

By Leonie Valentine and Richard Hobbs

Fire management around Perth may hold the key to the future of an endangered cockatoo.

The gregarious Carnaby’s cockatoo is such a common sight in Perth that it is easy to forget it is endangered and that the urban and agricultural expansion of south-western Australia has removed the bulk of its habitat. How we manage their remaining habitat will have important consequences for the species’ survival.

South-western Australia has undergone extensive habitat loss from agricultural and urban development. Less than 30% of the original vegetation now remains. As a consequence, the endemic Carnaby’s cockatoo has experienced widespread loss of nesting and feeding habitat and is considered endangered under the IUCN Red List, as well as Australian federal and state legislation. Since the 1950s, numbers of the Carnaby’s cockatoo have declined by more than 50%, with its range contracting by over 30%.

Carnaby’s cockatoo forages predominantly upon seeds in coastal areas during the non-breeding season (January–June), with most adults migrating to the inland wheat belt during winter to breed. Food is limited in both their breeding and non-breeding range.

The largest population of birds during the non-breeding season is found north of rapidly growing Perth. In this fragmented peri-urban and rural environment, birds feed on seed from dominant native banksia species in remnant native vegetation. They will also feed on the introduced maritime pine in plantations and other species. Where they occur, the pine plantations replaced native vegetation, and Carnaby’s cockatoos have a strong ecological association with this introduced food. The pine plantations are now being harvested, and their removal will further reduce food availability, increasing their reliance on native species in this increasingly fragmented landscape.

Fire plays a major role in maintaining the structure and function of ecosystems, and is a broadly utilised management tool. Fire and conservation management is particularly complex in fragmented peri-urban areas, where there are multiple, often conflicting, objectives to fire management.

Fire management will influence the resources available for fauna. Consequently, if fire management is to play a role in the conservation of biodiversity it needs to be done with an understanding of the requirements of target species. A critical element for successful fauna management in fire-prone ecosystems is to understand how management impacts resource availability.

To understand how fire influences food availability in the banksia woodlands we examined how the time since fire influences plant and cone densities of the two dominant native woodland food species: Banksia attenuata and B. menziesii). We then estimated the number of Carnaby’s cockatoo that would be supported in different post-fire aged banksia woodlands. We measured 44 sites of varying post-fire aged vegetation. The number of Carnaby’s cockatoos that could be supported in banksia woodlands was estimated using the bird’s energetic requirements and seed energy content.

Banksia attenuata produced more cones at sites aged 10–30 years since fire in both survey years, while cone productivity for B. menziesii was highest in very old sites (>35 years since fire) in one year only. We predicted that higher numbers of Carnaby’s cockatoos would be supported in vegetation aged 14–30 years since fire, peaking in vegetation aged 20–25 years.

The current distribution of post-fire aged vegetation within this area (>60% burnt within the past 7 years) is predicted to support around 2725 Carnaby’s cockatoos, representing 25–35% of the estimated birds that rely on the area. Our results indicate that food resources are influenced by the time since fire.

Therefore, if optimising food resources is an objective, the availability of food may be manipulated by altering burning patterns. Importantly, this would involve retaining greater areas of woodland burned with less frequency.

Current fire management is focused on human and asset protection as a priority for prescribed burning. If management of landscapes for improved persistence of threatened species is also considered important, then complex trade-offs may have to be considered. However, it would be possible to modify existing practices to achieve multiple goals if, for instance, a zoning approach was adopted that maintained frequent fire close to housing and infrastructure but allowed longer fire-free periods elsewhere.

Such solutions require more planning and effort, but if we desire a future that includes the existence of iconic species such the Carnaby’s cockatoo then it’s an effort we should all be demanding.

Leonie Valentine and Richard Hobbs are members of the Environmental Decisions Group at the University of Western Australia.