Foraging preferences of Swift Parrots on Tasmanian Blue-gum: tree size, flowering frequency and flowering intensity
Raymond Brereton A , Stephen A. Mallick B D and Simon J. Kennedy CA Forest Practices Unit, Patrick Street, Hobart, Tas. 7001, Australia.
B Department of Primary Industries, Water and Environment, 134 Macquarie Street, Hobart, Tas. 7001, Australia.
C Department of Natural Resources and Environment, Bendigo, Vic. 3550, Australia.
D Corresponding author. Email: stephen.mallick@dpiwe.tas.gov.au
Emu 104(4) 377-383 https://doi.org/10.1071/MU03045
Submitted: 11 September 2003 Accepted: 3 May 2004 Published: 16 December 2004
Abstract
The Swift Parrot (Lathamus discolor), is a migratory species that forages primarily on Blue-gum (Eucalyptus globulus) during its Tasmanian breeding season. We investigated the foraging preferences of Swift Parrots for Blue-gum trees of different sizes and the effect of tree size on flowering frequency and flowering intensity over three seasons (1998, 1999, 2001). Swift Parrots showed a clear preference for larger Blue-gum trees: Blue-gum trees in which Swift Parrots foraged were ~40% larger than surrounding (non-forage) trees, while the size-class distribution of forage trees was significantly skewed towards larger tree-size compared with surrounding non-forage trees. The mean flowering intensity of forage trees was also significantly greater than the mean flowering intensity of non-forage trees. Both flowering frequency and flowering intensity increased with tree size, although there was a trend for both flowering frequency and intensity to decline in the largest tree size-classes. Past clearing has resulted in the loss of over 50% of the original (pre-European) grassy Blue-gum forest in Tasmania. Remnant grassy Blue-gum forest as well as artificially planted Blue-gum trees typically occur in small patches of <1 ha, including many solitary and scattered trees in pasture, parkland and gardens. These isolated patches of Blue-gum frequently include trees of large stature, making them an important food resource for the endangered Swift Parrot.
Acknowledgments
This study was funded by the Natural Heritage Trust and administered by the Tasmanian Department of Primary Industries, Water and Environment. Peter Brown provided comments on an earlier draft of the manuscript. P. Tilyard and B. Potts (Cooperative Research Centre for Sustainable Production Forestry, School of Plant Science, University of Tasmania) provided data on Blue-gum flowering in south-eastern Tasmania.
Crowley, G. M. , and Garnett, S. T. (2001). Food value and tree selection by Glossy Black-Cockatoos Calyptorhynchus lathami. Austral Ecology 26, 116–126.
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