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Abstract

Male budgerigars may be limited in the time they have available to pursue extra-pair copulations because of conflicts with other reproductive behaviour. If males could selectively court only immediately fertilizable extra-pair females they should do so. The cere colour of a female budgerigar may be used as a cue to her reproductive readiness. We experimentally tested the hypothesis that males prefer females with dark ceres, which are indicative of developed ovaries, over females with light-coloured ceres, characteristic of birds with undeveloped ovaries. In a pairwise choice experiment between females that had their cere colour artificially manipulated, pair-bonded males were more likely to choose the female with the dark-coloured cere.