Food Resources of Carnaby’s Black-Cockatoo (Calyptorhynchus latirostris) in the Gnangara Sustainability Strategy study area

Carnaby’s Black-Cockatoo is an endangered species, with less than 50% of the original population remaining (Garnett and Crowley 2000). A major threatening process includes habitat fragmentation and the removal of critical feeding resources (Cale 2003). The GSS study area in an important foraging area during the non-breeding season for Carnaby’s Black-Cockatoo. Both native banksia woodlands and pine plantations have been recognised as an important food resource (Perry 1948; Saunders 1974b; Saunders 1980). Expanding urban populations and agricultural development has resulted in the removal of approximately 50% of native vegetation in the GSS study area. Within the remnant vegetation, the energetics, occurrence and densities of principal native food sources (e.g. Banksia attenuata) is still largely unknown, but varies depending on soil type, vegetation complex and fire history (Heddle et al. 1980; Scott and Black 1981; Valentine and Stock unpublished data). In addition, there are a number of limitations with the existing data, and further research is required to accurately estimate the availability of food resources. The predicted removal without replacement of the pine plantations is expected to impact on Carnaby’s Black-Cockatoo (Cale 2003; Garnett and Crowley 2000). The amount of food resources in the GSS pine plantations currently available to Carnaby’s Black- Cockatoo is predicted to be able to support over 10,000 birds for a 6 month period (with a prior mentioned caveats). If preliminary foraging behaviour data is incorporated, it is likely that the pine plantation will support approximately 2,800 birds for a 6 month period. Food resources in remnant Banksia attenuata habitat in the GSS study area vary depending on the landform and year since last burn (Valentine and Stock, unpublished data). The combined area of Bassendean North and Cottesloe North vegetation complexes (~ 25,000 ha) within DEC estate in the GSS study area could provide the minimum requirement of food for a maximum of approximately 18,500 birds for a 6 month period. However, incorporating preliminary foraging behaviour data reduces this estimate to approximately 4,900 birds for a 6 month period. The pine plantations provide an enormous food resource for Carnaby’s Black-Cockatoos. Regardless of the availability of native food sources, removing this amount of resource will affect Carnaby’s Black-Cockatoo in some manner. Assuming the remnant vegetation provides sufficient food resources for Carnaby’s Black-Cockatoos, the birds may simply switch foraging behaviours and diets to principally native species. However, if native food availability is limited, the removal of pine plantations may have greater impacts. Birds may search elsewhere for food during the non-breeding season, possibly switching diets to commercial agricultural crops (e.g. canola), and the populations on the Swan Coastal Plain may dwindle. In addition, if food is limited during the non-breeding season, birds may starve or enter the breeding season in poor condition, which is likely to affect breeding success, and ultimately population growth. Our review and preliminary research reinforces the importance of food resources on the Swan Coastal Plain (from both banksia woodlands and pine plantations), and highlights the urgent need to more accurate research into the availability of food resources and foraging ecology of Carnaby’s Black-Cockatoo