Foraging ecology of the South Australian glossy black-cockatoo (Calyptorhynchus lathami halmaturinus)

The endangered South Australian glossy black-cockatoo (Calyptorhynchus lath ami halmaturinus Mathews 1912) feeds almost exclusively on the seeds of the drooping sheoak (Allocasuarina verticillata), and shows marked preferences for individual trees. This field study investigated foraging ecology and t ree selection through observations of foraging birds and measurements of tr ees and seed cones. The cockatoos spent the vast majority of their foraging time (94%) handling seed cones, and handling behaviour was highly stereoty ped. Handling time per cone was correlated primarily with cone size, while seed intake rate was correlated primarily with seed mass per cone. The cock atoos fed mostly in trees with signs of previous feeding. They tended initi ally to sample trees with large seeds, and to stay for long feeding bouts i n trees with high ratios of seed-to-cone mass. As a result of these biases, feeding was concentrated in trees with high seed mass per cone. Preferred trees were also larger, with higher ratios of seed-to-cone mass and larger seeds containing more lipid and protein. By feeding from selected trees the cockatoos increased both their seed intake rate and the nutritional qualit y of the seeds ingested, thereby increasing their energy intake rate by an estimated 28%. They did not discriminate against trees that had re-grown fr om basal shoots after fires. Insect larvae were present in some seed cones but the cockatoos did not appear to actively seek them. Males foraged 19% m ore efficiently than females, resulting in greater daily food intake. The c haracteristics of individual A. verticillata trees that determined the cock atoos' feeding rates were also correlated with their distribution on a regi onal scale. This suggests that the distribution of this endangered cockatoo depends not only on the presence of food trees, but also on their regional ly varying feeding profitability.