Characteristics of nest trees and nest hollows used by the forest red-tailed black cockatoo (Calyptorhynchus banksii naso) in south-west Western Australia: comments on Johnstone et al. (2013)

Abstract

Johnstone et al. (2013) (Pacific Conservation Biology 19, 122–141) make a substantial contribution to the knowledge of the forest red-tailed black cockatoo (Calyptorhynchus banksii naso) (FRTBC), presenting data on nest hollows and nest tree attributes. They discuss the threats to the current and future breeding hollows and conclude that ‘we are facing a major crisis in southern forests’. Although there are sound reasons for concern over the conservation of cockatoo species, the imminence of a crisis is not established by the data presented. We provide spatial and management context and present data relevant to discussion of threats to FRTBC hollows in south-west Western Australia. The primary strategy for providing habitat across the publicly owned forests is reservation, which formally excludes timber harvesting from more than 50% (1.3 million ha) of the forest, informally protects a further 11%, and protects habitat trees within harvested areas. Timber harvesting in these forests generally involves partial cutting, which retains trees of a wide range of size and age classes. A realistic minimum age for trees bearing hollows used by FRTBC in the jarrah (Eucalyptus marginata) forest is ~120–150 years (trees diameters of 50–60 cm), well below the 209 years highlighted by Johnstone et al. (2013). Most nest hollows occur in intermediate-sized trees. Clustering of FRTBC nest trees was not demonstrated in their data but is worthy of further investigation. Improved estimates of nest tree availability and loss would provide perspective on the threats to FRTBC, as would knowledge of population size and age structure of the FRTBC. The protection of known nest trees and control of feral competitors, where possible, would benefit FRTBC.