Timing and Use of Paternity Guards By Male Chaffinches

I studied the relative timing and extent to which male chaffinches used two alternative paternity guards, frequent copulation and mate guarding by close following. Males guarded their mates strongly, and guarding peaked in intensity on day -2 relative to laying. Male mate guarding intensity varied predictably with the value of the female to the male in three ways: (a) guarding intensity increased from day to day as laying approached, as does the risk of a single EPC fertilizing an egg. (b) Males reduced their level of guarding when their females laid the penultimate egg of the clutch and were therefore no longer fertile. (c) The diurnal pattern of guarding varied with respect to whether laying had begun, which might represent a male response to an 'insemination window', when sperm would be less likely to fertilize an egg. Males also copulated frequently with their mates, with a peak rate of 4.4 copulation attempts per hour on day -3 relative to laying, with an estimated total of 207 copulation attempts (83 successful) per clutch. The peak in copulation frequency occurred earlier than the peak in mate guarding intensity. Males did not show any behavioural response to an increased risk of extra-pair copulations, assessed by the proportion of neighbouring males that were free to seek extra-pair copulations. I propose that in chaffinches frequent copulation is a relatively 'low-cost, high-risk' paternity assurance mechanism compared to mate guarding, and that the mechanism males employ depends upon the amount of information that males have about whether the female is going to lay, which represents the value of the female to the male. Fine-tuning of male behavioural mechanisms with the female value as a resource provides good evidence that the mechanisms are adaptations to sperm competition.