Ardea
Official journal of the Netherlands Ornithologists' Union

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Zenatello M., Serra L. & Baccetti N. (2002) Trade-offs among body mass and primary moult patterns in migrating Black Terns Chlidonias niger. ARDEA 90 (3): 411-420
Primary moult and long-distance migration entail high energetic costs, which birds usually minimise by keeping the two processes separated. Post-breeding migration and primary moult largely overlap in the Black Tern Chlidonias niger, and two moult patterns associated with different body masses are observed. Early in the season there is a high proportion of heavy birds (average mass 65.5 4.4g), which moult 2-4 primaries at a low growth rate; later on, there are mainly lean birds (63.0 4.7 g), which moult 1-3 primaries at a high growth rate. Despite differences in the growth rate of feathers, the timing of primary shedding is similar in the two groups. Suspension of primary moult and migration with old primaries involves a minority of individuals with low body masses (62.5 5.7 g and 62.2 4.1 g, respectively). Heavy-moulting birds have higher flight costs than weak-moulting birds, because their wing loading is higher and their larger moult gap requires a longer time to be filled. It is suggested that the low growth rate of heavy-moulting birds allows the production of better-quality feathers, which may enhance survival during the season between the two migration flights. This may be extremely important in this species, which strongly depends upon flight performance throughout the life cycle


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