Ardea
Official journal of the Netherlands Ornithologists' Union

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Marchesan M. (2002) Operational sex ratio and breeding strategies in the Feral Pigeon Columba livia. ARDEA 90 (2): 249-257
The operational sex ratio (OSR) is the ratio of fertilisable females to sexually active males in a population. The aim of this study was to determine the effects of OSR variations on pair bond dynamics and on the level of sperm competition in the Feral Pigeon Columba livia, a socially monogamous bird with long-term pair bonds. Both the overall level of breeding success and the stability of pair bonds were affected by changes in the OSR. When the OSR was male-biased breeding success was lower, largely due to egg damage, and divorce rates were higher than when the OSR was 1:1. However, the intensity of sperm competition did not appear to be related to the OSR: there were no differences in the patterns of extra-pair copulations between the two OSR regimes, and the patterns of pair and pair-switching copulations were not consistently affected by changes in the OSR. The results suggest that a male-biased OSR may indirectly affect the intensity of intrasexual competition in a population, through egg damage by the unpaired males. Egg damage may be a form of infanticide adopted by unpaired males as a sexually selected strategy to induce breeding failure, hence decreasing the level of pair bond stability and increasing the probability of pairing with a divorced female


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