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Prospective infanticide and ovulation retardation in free-living house sparrows

Abstract Abstract. Replacement male house sparrows, Passer domesticus , invariably committed infanticide when they took over a nest after a female's fertile period had recently ended ( N = 8). Males that took over a nest during egg laying destroyed eggs in 58% of the cases ( N = 12), whereas those arriving before clutch initiation never committed infanticide ( N = 32). Seven out of 12 nests in which the replacement male arrived during laying suffered egg losses (58%). In six of them the female owner stopped laying, while the remaining female left her nest. Two more females whose original males were replaced during the laying period (17%) and two out of seven females whose males were replaced during the 4 days prior to clutch initiation (29%) stopped laying even though they had not suffered egg losses. In contrast, females that initiated laying 5 days or more after the arrival of the replacement male did not stop laying. Nine out of 11 females initiated a new clutch with the replacement male on average 7·3 days after they stopped laying. The results suggest that male prospective infanticide functions to ensure genetic paternity, and that females use strategic ovulation retardation to cope with the risks of infanticide.