Short-term changes in body condition in relation to habitat and rainfall abundance in American redstarts Setophaga ruticilla during the non-breeding season

In migratory birds, environmental conditions during the stationary period of the non-breeding season are crucial to consider because they ultimately affect the fitness of individuals by influencing their subsequent migration, breeding success and survival. Although a few studies have investigated the influence of non-breeding habitat on the capacity of individuals to cope with long-term seasonal rainfall fluctuations, it remains unknown how habitat quality and variations in rainfall abundance-at a monthly scale-interact to affect non-breeding condition of migrating birds. In this study, we examined the influence of monthly changes in rainfall abundance on body condition of non-breeding female redstarts Setophaga ruticilla living either in a high quality habitat (mangrove) or in a low quality habitat (scrub). Body condition of both mangrove and scrub redstarts showed important variations over the study period, demonstrating for the first time that body condition of non-breeding female redstarts can change rapidly in response to short-term fluctuations in rainfall. Importantly, we found that female redstarts living in mangrove were usually in better condition during periods of low rainfall compared to females living in scrub. However, body condition did not differ between mangrove females and scrub females during an episode of frequent, heavy precipitation. Importantly, our study also demonstrated that the duration of a perturbation is an important determinant of body condition in redstarts since a prolonged drought resulted in similar low body condition for birds from both habitats. Age was not correlated with body condition whatever the habitat and the rainfall conditions. Our results demonstrate that high quality habitat can temporarily reduce the deleterious effect of a short-term drought on body condition, but also, that a habitat of low quality does not constrain individuals when climatic conditions are optimal.