Discrimination among potential buloke (Allocasuarina leuhmannii) feeding trees by the endangered south-eastern red-tailed black-cockatoo (Calyptorhynchus banksii graptogyne)

Abstract

Remnant buloke (Allocasuarina luehmannii) woodland and scattered buloke trees appear to provide an important seasonal food resource for the endangered south-eastern red-tailed black-cockatoo (Calyptorhynchus banksii graptogyne). The factors that differed between buloke trees in which the cockatoos fed and those in which they did not feed were investigated in two consecutive years (Season 1 and Season 2). Tree diameter at breast height (DBH), individual mean seed dry mass, individual mean cone dry mass, mean number of seeds per cone, and proportion of total cone mass comprising seeds (seed ratio) were all significantly greater in feeding than non-feeding trees in both Season 1 and Season 2. A predictive model incorporating these five variables correctly classified 83% of trees measured in Season 1 as either feeding or non-feeding trees. Validation of predictive models with new data is essential in evaluating model performance, so the model was used to classify the feeding and non-feeding trees from which the variables were recorded during Season 2. The model, although derived only from the data collected during Season 1, was equally as effective in predicting the feeding status of trees in Season 2, despite the fact that the trees in which the cockatoos fed during the second year were not the same individual trees as those used in the previous year. The differences between feeding and non-feeding trees suggested that cockatoos choose to feed in trees in which they are able to optimise their foraging efficiency. As individual buloke trees appear to vary in their suitability for cockatoo foraging from year to year, it is not possible to exclude any buloke within the range of the cockatoo as a potential future food resource for this endangered bird.