Moulting fast and time constraint for reproduction in the king penguin

King penguins (Aptenodytes patagonicus) replace their complete plumage during a 3- to 4-week moulting fast on shore. After moulting, birds forage at sea for 2-3 weeks to store energy reserves for reproduction. Using an automatic identification and weighing system coupled with visual observations. we investigated the trade-off between the moulting fast and the following breeding attempt, in terms of body condition and in relation to time constraints, in free-living king penguins. King penguins reached their lowest body mass of the yearly cycle at the end of the moulting fast, this was lower than that at the end of the incubation fasts and not different from the body mass at egg desertion. Later in the season. the duration of the moulting fast became shorter and old feather loss occurred earlier after arrival ashore. Postmoulting foraging trips were shorter, but at the expense of body condition at the beginning of Courtship. These results are discussed in relation to the synchronisation of the breeding cycle with food availability and mate choice.