Although grooming and other kinds of maintenance activity are important components of the behavioural repertoire of terrestrial vertebrates, comparative studies of the proportion of time budgets devoted to maintenance are lacking. Data were collated on the proportion of their time-budgets devoted to maintenance behaviour by 62 different bird species. On average, birds spend 9.2% of the day in maintenance activities, with the major component (92.6%) being grooming. Male birds devoted more time to maintenance than females, except in the case of ducks. Maintenance time does not appear to correlate with morphology, moult, latitude, coloniality or season. However, bird species known to harbour more parasitic louse species spend more time on maintenance than do host species with few lice.