Consequences of variation in brood size on the allocation of parental care in common terns (Sterna hirundo)

Data on the behaviour of common tern (Sterna hirundo) parents were analyzed to document shifts in parental care patterns with changes in brood size. The primary roles of the sexes, chick feeding by males, and brood attendance by females, did not change with shifts in brood size. Rather, parents simply altered the amount of care provided. One-chick broods received more parental attendance at the nest site than both two- and three-chick broods, likely as a result of the increased foraging effort of two- and three-chick parents. The number of chick feeds per hour increased significantly with each increase in brood size, but the number of feeds of each chick per hour did not. Thus, although parents increased their foraging effort with increasing brood size, the net effect was that chicks in all brood sizes were fed at similar rates.