Food Value and tree selection by Glossy Black-Cockatoos Calyptorhynchus lathami

Glossy Black-Cockatoos (Calyptorhynchus lathami) appear to maximize dry mat ter intake by selecting feeding trees that have the most profitable seed cr ops as indicated by Clout's Index (seed weight/total cone weight). However, as it is unlikely that cockatoos can directly assess Clout's Index, the me chanism for such selection is unclear. Moreover, as cockatoos consume only the kernels, and not all seeds contain kernels, better estimates of food va lue are required. Therefore, we examine seed and cone characteristics and e stablish that Seed Fill (percentage of seeds containing kernels) and Kernel Ratio (average kernel weight/average cone weight) contribute significantly to Food Value (weight of kernels/total cone weight). We propose that these factors can be rapidly assessed by cockatoos, and show that selection of f eeding trees can be more accurately predicted using discriminant analysis w ith a combination of Seed Fill and Kernel Ratio than with either Food Value or Clout's Index alone. Along with most other characteristics, Seed Fill a nd Kernel Ratio were consistent between the two years of study, enabling fo raging cockatoos to return to profitable trees annually, without sampling. Where sampling is undertaken, rapid assessment of profitability by sampling cone ends is possible, as kernels are randomly distributed through the con e. Also, a decline in Food Value, Seed Fill and Kernel Ratio with cone age, means that cockatoos could also assess profitability on the basis of cone colour. We show that concentrations of individual nutrients are unlikely to contribute to tree selection, previous reports of such selection being cau sed by the predominance of protein and oils in the kernels, and of ash, fib re and carbohydrates in the samara. We therefore conclude that cockatoos se lect feeding trees primarily on the basis of optimizing kernel intake.