Burning questions for black cockatoos

Fire may hold the key to the future of Carnaby’s cockatoo

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

Carnaby’s cockatoos feed on the seeds of a variety of native and introduced plant species and on insect larvae. Plants include kwongan heath plants such as banksias, dryandra, hakea, grevillea and also marri seeds. New research suggests fire management may make an important contribution to sustaining the cockatoo’s food sources. (Photo by Leonie Valentine)

Carnaby’s cockatoos feed on the seeds of a variety of native and introduced plant species and on insect larvae. Plants include kwongan heath plants such as banksias, dryandra, hakea, grevillea and also marri seeds. New research suggests fire management may make an important contribution to sustaining the cockatoo’s food sources.
(Photo by Leonie Valentine)

A species under pressure 

South-western Australia is a global biodiversity hotspot that has undergone extensive habitat loss from agricultural and urban development. Less than 30% of the original vegetation now remains. As a consequence of this habitat loss, the endemic Carnaby’s cockatoo has experienced widespread loss of nesting and feeding habitat and is considered endangered under the IUCN Red List, and 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%. The species has disappeared from more than a third of its former breeding areas.

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 the Austral winter to breed. Foraging resources are limited in both the breeding and non-breeding range for this species.

If optimising food resources was 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.” 

The largest population of birds during the non-breeding season is to be found north of Perth, one of the most rapidly growing cities in Australia. In this fragmented peri-urban and rural environment,

birds feed on seed from dominant native species Banksia attenuata and B. menziesii in remnant native vegetation. They will also feed on the introduced maritime pine (Pinus pinaster) in plantations and other species. Where they occur, the plantations replaced native vegetation, and Carnaby’s cockatoos have a strong ecological association with this introduced food. Currently, the pine plantations are being harvested and their removal will further reduce food availability increasing their reliance on native species in this increasingly fragmented landscape.

Fig.1. Generalised Additive Model Relationships for the a) predicted number of Carnaby’s cockatoos supported in 100 ha of banksia woodland (Y) with time since fire (±95% CI; adjusted r2 = 0.35 for square-root transformed variable), and b) predicted number of Carnaby’s cockatoo supported in 100 ha of banksia woodland, adjusted for foraging efficiency (Y*) with time since fire (±95% CI; adjusted r2 = 0.35 for square-root transformed variable). Symbols represent the different combinations of landform type (Bassendean or Spearwood) and year of survey (2008 or 2010). (From Valentine et al 2014.)

Fig.1. Generalised Additive Model Relationships for the a) predicted number of Carnaby’s cockatoos supported in 100 ha of banksia woodland (Y) with time since fire (±95% CI; adjusted r2 = 0.35 for square-root transformed variable), and b) predicted number of Carnaby’s cockatoo supported in 100
ha of banksia woodland, adjusted for foraging efficiency (Y*) with time since fire (±95% CI; adjusted r2 = 0.35 for square-root transformed variable). Symbols represent the different combinations of landform type (Bassendean or Spearwood) and year of survey (2008 or 2010).
(From Valentine et al 2014.)

Habitat under fire 

Fire plays a major role in maintaining the structure and function of ecosystems and is a broadly utilised management tool,

implemented by humans for a variety of purposes. 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 individual requirements of target species and community dynamics. A critical element for successful fauna management in fire prone-ecosystems is to understand how management actions affect resource availability.

To understand how fire influences food availability in the banksia woodlands we examined how time-since-fire influences plant and cone densities of the two dominant native woodland food species (B. attenuata and B. menziesii). We then estimated the number of Carnaby’s cockatoo that would be supported in different post-fire aged banksia woodlands (including an estimation of the number of Carnaby’s cockatoo that could be supported with the current distribution of post-fire banksia woodland habitat) (Valentine et al 2014).

Fire and food

We compared tree density and cone productivity of dominant banksias across 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, and accounting for some aspects of their foraging ecology.

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 between 14-30 years since fire, peaking in vegetation aged 20–25 years (Figure 1).

The current distribution of post-fire aged vegetation within this area (>60% burnt within the last 7 years) is predicted to support around 2,725 Carnaby’s cockatoos, representing 25–35% of the estimated birds reliant on the area. Our results indicate that food resources are influenced by time since fire. Therefore, if optimising food resources was 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, understandably, 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 effort we should all be demanding.


Flocks of Carnaby’s cockatoo are a familiar sight in Perth skies, and their calls evoke a strong sense of place. (Photo by Leonie Valentine)

Flocks of Carnaby’s cockatoo are a familiar sight in Perth skies, and their calls evoke a strong sense of place.
(Photo by Leonie Valentine)

How many are there?

It is difficult to know how many Carnaby’s Black-Cockatoos are left, but it is known that their populations have declined by over 50% in the past 45 years, and that they no longer breed in up to a third of their former breeding sites in the Wheatbelt.

They are gregarious birds and live in pairs or small flocks during the breeding season. After fledging, the young move with their parents from breeding areas to feeding areas where other family groups join the flock.

The cockatoos live for 40-50 years in the wild. A large proportion of the remaining population now is past breeding age. When these older birds die, there will be very few younger birds to take their place.

More info: http://www.environment.gov.au/biodiversity/threatened/publications/factsheet-carnabys-black-cockatoo-calyptorhynchus-latirostris 


More info: Richard Hobbs richard.hobbs@uwa.edu.au 

Reference 

Valentine LE, R Fisher, BA Wilson, T Sonneman, WD Stock, PA Fleming & RJ Hobbs (2014). Time since fire influences food resources for an endangered species, Carnaby’s cockatoo, in a fire-prone landscape. Biological Conservation 175: 1–9.

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