Theft of bower decorations among male Satin Bowerbirds (Ptilonorhynchus violaceus): why are some decorations more popular than others?
Janine M. Wojcieszek A C , James A. Nicholls A D , N. Justin Marshall B and Anne W. Goldizen A EA School of Integrative Biology, University of Queensland, St Lucia, Brisbane, Qld 4072, Australia.
B Vision, Touch and Hearing Research Centre, School of Biomedical Sciences, University of Queensland, St Lucia, Brisbane, Qld 4072, Australia.
C Present address: Department of Terrestrial Invertebrates, Western Australian Museum, Locked Bag 49, Welshpool, D. C. Perth, WA 6986, Australia.
D Present address: Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom.
E Corresponding author. Email: a.goldizen@uq.edu.au
Emu 106(3) 175-180 https://doi.org/10.1071/MU05047
Submitted: 8 September 2005 Accepted: 17 May 2006 Published: 18 August 2006
Abstract
Male Satin Bowerbirds (Ptilonorhynchus violaceus) build stick structures known as bowers that serve as the focus for courtships and matings. Males decorate their bowers with numerous coloured decorations and are known to steal these decorations from one another. We investigated the stealing of bower decorations among males at the Bunya Mountains in Queensland, Australia. We aimed to (1) determine which classes of decorations were targets for theft in the studied population, and (2) examine whether the frequency at which individual decorations were stolen related to their intrinsic properties. To address our first aim, all decorations on the bowers of 21 adult males were labelled and their movements tracked throughout one mating season. To address our second aim, decorations stolen at least three times during the season were collected and their morphological and reflectance properties compared to those of decorations that were not stolen. In terms of the classes of decorations, tail feathers of Crimson Rosella (Platycercus elegans) were stolen more than any other class of decoration, but blue plastic bottletops were the most popular decorations relative to their availability on bowers. Frequently stolen individual decorations were similar to non-stolen items in their weights and surface areas, but were darker blue in colour than the decorations never stolen. Both bottletops and feathers reflected higher levels of ultraviolet (UV) light than did all other classes of bower decorations tested, thus suggesting that males may be using UV reflectance in sexual signalling. The darker blue, stolen decorations may increase contrast between the decoration collection and the platform, while the UV-reflecting subset of most frequently stolen decorations (bottletops and feathers) may increase contrast within the decoration collection. This in turn may increase the attractiveness of the display to females.
Acknowledgments
We thank the Stirling and Foxton families for allowing us to work on their properties, the Bjelke-Peterson family for allowing us to rent their property, and all of the field assistants for their time and assistance. Funding for this study was provided by the University of Queensland and the Australian Research Council.
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