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Para realizar o presente estudo tive que bater em várias portas, muitas delas permitiram o meu ingresso com a minha mala cheia de corujas, outras permaneceram em silêncio. Sou grato a todos aqueles que acreditaram nesta bonita jornada. Juntos, estamos contribuindo de diferentes formas em prol dos animais silvestres.Ao meu Orientador, Prof. Dr. Claudio Alvarenga de Oliveira, por me receber em seu grupo de pesquisa e permitir a realização de todos os projetos idealizados, obrigado pela confiança que o senhor depositou em mim.A MSc. Carolina Lorieri Vanin, minha amiga-irmã que São Paulo me deu, que esteve sempre disponível sem se importar o quão ocupada estivesse.

Glucocorticoids mediate physiological processes to obtain energy, presenting daily variation in basal levels that may be related to behavioural activity pattern. Identification of plasticity in the secretion of these hormones is essential to understand their effects on physiology and behaviour of wild birds and, therefore, their success in their natural or artificial environment. Serial endocrine evaluations are facilitated by implementing non-invasive methodologies that minimize possible effects of manipulation on the animal’s physiological variables. However, non-invasive endocrine-behavioural studies in nocturnal birds, such as owls, are immature. The present work aimed to validate an enzyme immunoassay (EIA) to quantify glucocorticoid metabolites (MGC) in Megascops choliba as well as to evaluate differences in their production at the individual, sexual or daily level. We recorded the behaviour of nine owls during three continuous days to establish activity budget under captive conditions and aiming to correlate with daily MGC variation. The EIA proved to be effective in analytical assays and in pharmacological testing with synthetic ACTH, validating this immunoassay for the species. Additionally, individual differences in MGC production were confirmed in relation to the time of day, especially at 1700 and 2100, but not in relation to sex. During night hours, the owls showed greater behavioural activity, positively related to MGC values. Higher MGC concentrations were significantly related to greater expressions of active behaviours, such as maintenance, while lower MGC concentrations were recorded during moments of higher alertness and resting. The results presented show daily MGC variation to be inversed in this nocturnal species. Our findings can aid future theoretical studies of daily rhythm and evaluations of challenging and/or disturbing situations that result in changes in behaviour or hormonal cascades of these changes in ex situ populations of owls.

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