Abstract:
Relatively little effort has been directed towards elucidating the role of
physiological stress pathways in mediating avian responses to global
heating. For free-ranging southern pied babblers, Turdoides bicolor,
daily maximum air temperatures (Tmax) between ∼35 and ∼40°C
result in reduced foraging efficiency, loss of body mass and
compromised breeding success. We tested the hypothesis that very
hot days are experienced as stressors by quantifying relationships
between Tmax and faecal glucocorticoid metabolite (fGCM) levels in
naturally excreted droppings. On days when Tmax<38°C, fGCM levels
were independent of Tmax (mean±s.d. 140.25±56.92 ng g−1 dry
mass). At Tmax>38°C, however, fGCM levels increased linearly with
Tmax and averaged 190.79±70.13 ng g−1 dry mass. The effects of
Tmax on fGCM levels did not carry over to the following morning,
suggesting that very hot days are experienced as acute stressors.
