Ambient temperature and air pressure modulate hormones and behaviour in Greylag geese (Anser anser) and Northern bald ibis (Geronticus eremita)

• Vertebrates react to environmental variability by excreting glucocorticoids.
• In this study free-ranging Greylag geese and Northern bald ibis faced cold winter.
• We examined changes of corticosterone and behaviour with weather factors.
• Corticosterone and behaviour correlated with temperature and air pressure changes.
• These adjustments could optimise energy expenditure during premigration period.

Ambient temperature and air pressure are relevant stimuli that can elicit hormonal responses in alignment with adjusting individuals’ physiology and behaviour. This study investigated possible changes in corticosterone (C) and testosterone (T) and contingencies with behaviour in response to ambient temperature and air pressure, and it evaluated the temporal response dynamics of these hormones in 12 individual Greylag geese (Anser anser) over 26 and 12 individual Northern bald ibis (Geronticus eremita) over 27 days, during late winter. Immunoreactive metabolites of C and T were analysed non-invasively from 626 fecal samples by means of group-specific antibodies and correlated to behaviour and weather factors. In both species, high C levels correlated with low temperatures 24 h before sampling, but low C levels correlated with high air pressure 6–12 h before sampling. In both species, C levels and behavioural activity were negatively correlated. In addition, temperature had a positive influence on T levels in both species 12–24 h before sampling. The fact that weather conditions influenced changes in levels of C, while social interactions did not, is indicative of a general mechanism of graduated physiological adjustment to environmental variations affecting metabolism, stress responses and behaviour.