Although most (>90%) species of birds have biparental care, little is known about the consequences of such care for offspring behaviour and fitness-related traits. We examined the effect of biparental care on chick growth and begging behaviour in zebra finches, by comparing biparental broods with uniparental broods in which the male parent was removed and the brood size halved to control for potential parental workload. Differences in patterns of growth and begging behaviour between treatments therefore resulted from the difference in (1) the number of parents providing care and/or (2) the number of chicks per brood. Collaborating parents did not appear to act in concert and fed chicks independently of each other's feeding bouts. Broods reared by two parents were fed more frequently than those fed by one, and because biparental feeding bouts were less predictably spaced in time with less food available for each chick per feeding bout, competition was greater than in broods reared by single parents. Furthermore, chicks in biparental broods sustained an additional cost of begging: they had to beg almost twice as hard as chicks reared by single parents to receive a given amount of food, and they received less food per chick. Despite these effects, they grew faster. Growth rate may depend not just on the amount of food available but also on the frequency and predictability with which it is delivered, and, in particular, it reflects an adaptive response to competition for the available resources.