Parental effort by socially monogamous purple martins was measured to test the hypothesis that males reduce care in response to their risk of losing paternity through extra-pair copulations. Male martins occur in two age classes, with one-year-old males cuckolded in very high frequencies and older males achieving nearly complete paternity. This outcome is because females paired to young males pursue a mixed mating strategy of seeking extra-pair copulations, and females paired to old males avoid extra-pair copulations. Using multi-locus DNA fingerprinting to determine paternity, nb evidence was found that males reduced effort according to actual paternity or presumed confidence of paternity. Young and old males provisioned nestlings at similar rates in relative and absolute terms. There was also no relationship within the young age class, with young males provisioning similarly regardless of whether they were cuckolded. Young males achieving zero paternity provisioned similarly to young males achieving partial and complete paternity, suggesting that no threshold effect exists. Although several conditions have been proposed under which no relationship between paternity and male care is expected, these conditions did not exist for purple martins. Another condition under which males should not reduce care to unrelated offspring is proposed, namely, that performing poorly in the presence of potential future mates or extra-pair copulation partners can lower social status and thereby fitness. The 'status hypothesis' provides a perspective for viewing parental performance as a behavioural character on which sexual selection operates. (C) 1996 The Association for the Study of Animal Behaviour.