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1 July 2011 Interspecific Aggression for Nest Sites: Model Experiments with Long-Tailed Finches (Poephila acuticauda) and Endangered Gouldian Finches (Erythrura gouldiae)
Dhanya Pearce, Sarah R. Pryke, Simon C. Griffith
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For cavity-nesting birds, tree cavities often represent a critical, defendable, and limiting resource that is frequently under intense interspecific competition. However, the dynamics of interspecific conflict resolution, especially between species of similar size, are often unclear. We experimentally tested aggression and nest-defense behaviors in Gouldian Finches (Erythrura gouldiae) and Long-tailed Finches (Poephila acuticauda), two sympatric, cavity-nesting estrildid finches that are very similar in size, ecology, and nest-site requirements. Mounted taxidermie models of conspecific and heterospecific nest-site competitors (black and red Gouldian Finch morph and Long-tailed Finch models), as well as a control noncompetitor (Black-chinned Honeyeater [Melithreptus gularis]), were presented to Gouldian and Long-tailed finches. These two competing species differed in their overall responses to simulated intruders and in their relative aggression toward conspecific and heterospecific intruders. Long-tailed Finches reacted more quickly to models, approached closer, and were more likely to attack models (i.e., make physical contact) than Gouldian Finches, which suggests that Long-tailed Finches are intrinsically more aggressive. In addition, Long-tailed Finches were more aggressive toward Gouldian Finches than toward conspecific models. By contrast, Gouldian Finches were more aggressive to conspecific models and avoided approaching Long-tailed Finch models. Male Gouldian Finches were particularly aggressive toward conspecifics, and red head-color morphs were more aggressive than black morphs. These results suggest that the outcomes of competitive asymmetries within and between these species are driven by differences in aggression. Together with the substantial overlap in nest-site use, the Long-tailed Finch's aggressive domination of limited nest sites may lead to competitive exclusion of the endangered Gouldian Finch.

© 2011 by The American Ornithologists' Union. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press's Rights and Permissions website,
Dhanya Pearce, Sarah R. Pryke, and Simon C. Griffith "Interspecific Aggression for Nest Sites: Model Experiments with Long-Tailed Finches (Poephila acuticauda) and Endangered Gouldian Finches (Erythrura gouldiae)," The Auk 128(3), 497-505, (1 July 2011).
Received: 14 April 2011; Accepted: 25 May 2011; Published: 1 July 2011
cavity nesting
Erythrura gouldiae
Gouldian Finch
heterospecific aggression
interspecific competition
Long-tailed Finch
Poephila acuticauda
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