The social structure of the avocet, Recurvirostra avosetta, was investigated during the young rearing period. In the two colonies studied on the French Atlantic coast, in Vendée, family groups leave the nest site a few hours after hatching and go to the feeding areas. There, contiguous territories are vigourously defended by the two attentive adults for at least 6 weeks. Territory size, ranging from 260 to 5200 m2, according to the family, shows no clear temporal variation. However, these values are positively correlated with brood size. Within each family, differential use of the rearing territory as a structured area is revealed. (i) Daily distribution of the birds' activities such as feeding, resting, preening, watching is patchy; (ii) for a given activity, adults and chicks tend to use different areas, especially when foraging. The analysis of social relationships indicates that the two attentive adults spend little time near each other, whereas chicks tend to remain close to one another and adult behaviour varies according to the distance from the brood. Moreover, chicks are synchronized whereas the two parents tend to carry out different activities simultaneously. Social structure is viewed as a compromise between the territorial and the colonial types.
