Hard to fly the nest: A study of body condition and plumage quality in house sparrow fledglings

Contrary to the nestling phase, the post-fledging phase has been less studied probably because it is challenging to follow the chicks after they fledge. However, this phase is crucial to consider when focusing on the life cycle of individuals be- cause it is associated with new demands: After leaving the nest, individuals have to find their own food and cope with a new set of previously unknown stressors. In this study, we aimed at better understanding how energetically demanding the post-fledging period is in house sparrows Passer domesticus by measuring several indices of a fledgling's state (body condition, fat and muscle scores and plumage quality). If the energetic demands of the post-fledging period are greater than those of the adult life, we pre- dicted that fledglings should be in lower condition and should have a plumage of lower quality relative to adults. Supporting this prediction, the condition and the plumage of fledglings differed dramatically from those of adults. Interestingly, this difference disappeared in autumn. Overall, our results suggest that the post-fledging period is probably one of the most energetically de- manding of the life cycle in this species. Supporting this idea, the resighting probability of fledglings was lower relative to adults. However, resighting probability depends on many factors (mortality, dispersal, habitat use and behaviours) and future studies are necessary to tease apart their relative importance in determining resighting probability (Current Zoology 60 (4): 449-459, 2014).