Separating gregarious individuals from their group members often results in behavioural and physiological changes, like increased levels of corticosterone. Testosterone and corticosterone, in particular, have been implicated in the response of mammals to novelty. Data in birds are, however, rare. The presence or absence of group members may also influence an individual's response to novel stimu...

Marine predators, such as seabirds, are useful indicators of marine ecosystem functioning. In particular, seabird diet may reflect variability in food-web composition due to natural or human-induced environmental change. Diet monitoring programmes, which sample diet non-invasively, are valuable aids to conservation and management decision-making. We investigated the diet of an increasing popula...

The heterophil to lymphocyte (HL) ratio in the peripheral blood is increasingly being recognized as a reliable indicator of stress in birds. In this study we examined whether HL ratio, as well as the proportion of heterophils and lymphocytes, varied systematically with sampling time, date, age, climate conditions or with measures of maternal investment in female tree swallows (Tachycineta bicol...

In seasonallybreeding birds, natural selection favors individualsthat begin breeding earlier in a year because they produce more or higher quality offspring than those that begin breeding later. Among the factors that in uence the timing of breeding, which include the age, health, competitive ability, or mate quality of individuals, is the longevity of the pair bond, with birds that remain mat...

The propensity of migratory waders to remain on the non-breeding grounds during the arctic breeding season (‘‘oversummer’’) in their first biological year of life (‘‘juveniles’’) may be latitude, and thus migratory distance dependent. We compared the extent of preparation for northward migration of western sandpipers Calidris mauri spending the non-breeding season in México and Panamá during 19...

The pattern of fine-scale genetic structure in a population may reflect current biological processes of the species, such as natal dispersal, the breeding system and demography. We investigated the spatial distribution of nests and fine-scale genetic structure during two breeding seasons in a population of a weakly territorial, flock-living passerine bird, the vinous-throated parrotbill, Parado...