I quantified parental effort in biparentally caring Razorbills (Alca torda) to test whether variation in male effort was related to variation in their mates' receptivity to extra-pair copulations. On average, males contributed approximately equally to their mates in chick feedings and overnight nest attendance. There was, however, marked variation in relative male effort, with the proportion of male feeding relative to their mates' feeding ranging from 16 to 72%. No significant portion of this variation was explained by direct and indirect measures of males' confidence of paternity. Support was equivocal for an alternative hypothesis, that variation in male effort is caused by differential male ability, Male care increased significantly with fighting ability and mating arena attendance, but not with five other measures of male "vigor." I propose a second alternative hypothesis-that Razorbills and other long-lived, breeding-site-faithful species may reduce their social status over the long term by provisioning poorly, and that lowered status may decrease fitness. Thus, circumstances may exist under which it is beneficial for males to provide care for offspring that may not be their own.