Fine-scale dynamics of competitive fertilisation in social groups of red junglefowl (Gallus gallus) shed new light on avian sperm competition

Studies of birds have made a fundamental contribution to elucidating sperm competition processes, experimentally demonstrating the role of individual mechanisms in competitive fertilisation. However, the relative importance of these mechanisms and the way in which they interact under natural conditions remain largely unexplored. Here, we conduct a detailed behavioural study of freely-mating replicate groups of red junglefowl, Gallus gallus, to predict the probability that competing males fertilise individual eggs over the course of 10-day trials. Remating frequently with a female and mating last increased a male’s probability of fertilisation, but only for eggs ovulated in the last days of a trial. Conversely, older males, and those mating with more polyandrous females, had consistently lower fertilisation success. Similarly, resistance to a male’s mating attempts, particularly by younger females, reduced fertilisation probability. After considering these factors, male social status, partner relatedness and the estimated state of a male extragonadal sperm reserves did not predict sperm competition outcomes. These results shed new light on sperm competition dynamics in taxa such as birds, with prolonged female sperm storage and staggered fertilisations.