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In birds, the chick’s physical state at nest departure is critical for survival, especially for seabirds that shift from a terrestrial to a marine life. The timing of this life history transition should therefore be finely tuned by proximate factors reflecting the relative influence of parents and chicks. Using king penguins, Aptenodytes patagonicus, as a model, we investigated how food provisioning and chick developmental status and/or body condition interact with chick fledging behaviour to optimize the physical state at colony departure. During the month preceding colony departure, movements, developmental status and body condition were compared between naturally and experimentally fed chicks. Parents stopped feeding their moulting, obese chick on average 16 days before colony departure and no offspring anorexia was observed. All chicks left their feeding site at the time of moult end, indicating that complete feather development is a prerequisite for departing. The time between moult end and colony departure reduced both intra- and intergroup variation in body condition at departure, suggesting that this condition was optimized in terms of a trade-off between fat stores and buoyancy. After moult end, chicks increased their locomotor activity and energy expenditure, which contributes to the regulation of body condition. Our results indicate that the cessation of parental feeding does not trigger colony departure. Rather, the timing of departure depends on the chick’s physical state, regardless of its recent feeding history. Thus, in king penguins, the parental decision to desert the chick seems to reflect a compromise between the offspring’s body condition and its developmental status. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.