SummaryThe ability of juvenile and adult Black NoddiesAnous minutusto differentiate between related individuals was assessed by examining: (1) the feeding response of adults towards unfamiliar chicks, substituted in place of their own offspring; and (2) the relative behaviour of both adults and young when confronted with unfamiliar individuals. Results show that parent-chick discrimination in the Black Noddy can be detected some time in the fourth week post-hatching and is not correlated with chick movement from the nest. The recognition of both adults and nesting site was detected in the behavioural response of chicks over 28±2 days old. No equivalent discriminatory ability was observed in adults towards their own young at this age. Some discrimination by adults was observed if similarly aged chicks had prematurely fallen from the nest. This relative lack of adult discrimination and the intense nest site recognition by young may result from both pre- and most post-fledging care occurring at the nest. It is hypothesised that the discrimination by young, which occurs without corresponding adult recognition some 12–15 days before fledging, may be related to the period at which both adults are required to forage simultaneously. Once this occurs young begin to defend the nest site and need to distinguish between returning parents and potential intruders.