Individuals of many shorebirds may stay in their non-breeding grounds without travelling north for breeding. The frequency of oversummering has increased in the last decades in the black-tailed godwit (Limosa limosa). Potential reasons may involve climatic conditions and the increasing use of man-made habitats (rice-fields) and their interaction with individual's physiology. In this study we aim:

 To investigate the importance of physiological factors to explain the increasing fraction of non-reproductive individuals in some migratory species. The black-winged godwit (Limosa limosa) will be used as study species due to the dramatic drop in the number of breeding pairs in northern Europe and the increasing number of individuals that oversummer without breeding in Spain.
 To determine the importance of physiology in explaining the capacity of some species to maintain viable populations in the southern limit of their distribution range while others are disappearing due to climate change.
 To address the relationship between metabolic plasticity, immune capacity and exposure to pathogens in explaining the capacity of some species to maintain viable populations at the southern extreme of their distribution range