The breeding biology of the Forest Red-tailed Black Cockatoo Calyptorhynchus banksii naso Gould in south-western Australia. I. Characteristics of nest trees and nest hollows.

Abstract

The Forest Red-tailed Black Cockatoo Calyptorhynchus banksii naso (FRTBC) is a large, iconic forest cockatoo, endemic to the south-west corner of Western Australia. It is currently listed as Vulnerable under the State Western Australian Wildlife Conservation Act and under the Commonwealth Environment Protection and Biodiversity Conservation Act. In this paper, we provide details of nest tree and nest hollow requirements based on details of hollows in 128 nest trees studied over 17 years. FRTBC are monogamous and pairs nest in tree hollows from 6.5–33 m above ground. Most nests are in very large and very old, mature Marri Corymbia calophylla, a long-lived endemic tree species, which is the most important nesting tree throughout the FRTBC range. Nest trees of all species had a mean circumference at breast height of 2.79 m, a mean estimated age of 222 years and a mean overall height of 20.24 m. Marri nest trees had an mean circumference at breast height of 2.76 m, a mean estimated age of 220 years (95% confidence limit 209–231 years) and an average overall height of 20.04 m. The rate of fall or loss of nest trees was high, c. 16.6% per decade. A wide range of hollow types, defined by position of the hollow in the tree, were found. Hollow aspects were also diverse. The mean height to a hollow was 14.49 m. Mean hollow depth was 1.44 m, mean floor space (the longest linear distance across the bottom of the hollow) was 33.2 cm and the mean hollow entrance area was 30 x 34 cm. FRTBC nests are typically, but not always, clustered in the landscape and social interactions within the flock are likely to play a part in the clustering of nests. Nest competitors, including feral European Honey Bee Apis mellifera, Carnaby’s Cockatoo Calyptorhynchus latirostris, Baudin’s Cockatoo C. baudinii and the Regent Parrot Polytelis anthopeplus were recorded using nest hollows once used by FRTBC. In the past Marri was harvested commercially, especially the largest and oldest trees, for timber and woodchips. In recent times the volume of Marri logs has been reduced due to a decline in markets e.g. between 2004 and 2010 a total of 95,436 m³ was harvested (K. Whitford, pers. comm.). Given the importance of large, old trees for FRTBC breeding habitat, conservation of these trees