Estrildine finches are important model species in experimental studies on female mating preferences, but research has focused on only two species from this family, namely, the Zebra Finch Taeniopygia guttata and the Bengalese Finch Lonchura striata var. domestica, and we know comparatively little about other closely related species. Therefore, we investigated sexual dimorphism and female choice in the Java Sparrow Padda oryzivora, which also belongs to the family Estrildidae, to open up the potential for comparative research and to better understand sexual selection in this family. First, we took measurements of eight morphological traits of six male and six female Java Sparrows: natural wing length, maximum wing length, tarsus length, tail length, exposed culmen length, bill width, bill depth and body mass. We quantitatively confirmed that Java Sparrows show sexual dimorphism in bill depth, with males having deeper bills than females. Second, we examined individual variation in male courtship songs by analyzing their acoustic and syntactical structure. After collecting data on male morphological and song-related traits, we conducted two-way choice tests to ask which kinds of male traits predicted which males were preferred by female Java Sparrows. In the choice tests, we put a cage with a female in between two cages each containing one male and recorded the position of the female every 30 seconds by point sampling. We performed a stepwise regression analysis to assess the relationship between the time females spent in front of each male and male morphological and song-related traits. The results indicated that females base their preference upon large body size, which is likely to act as a good indicator of male quality. However, no preference was observed for song-related traits or sexually dimorphic bill depth. Perhaps the sexual dimorphism in bill size is instead the evolutionary outcome of male-male competition.
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Vol. 10 • No. 1