Adrenal response to competitive singing: glucocorticoid metabolites in male Saltator similis (Aves, Thraupidae).

Abstract

Song competitions involving passerines, such as the Green-winged Saltator (Saltator similis), are legally permitted in Brazil and attract widespread participation. This study aimed to assess the adrenal response in male S. similis by comparing glucocorticoid metabolite (GCM) levels in uro-faecal extract samples collected during three competitions with those from a rest day (3 days before the competition, D-3), a day before the competition (D-1), the day of the competition (D0) and a day after the competition (D1). Simultaneously, we examined the potential variation in GCM levels among other males not engaged in song competitions but subjected to ex situ conditions much like those of participating males. GCM levels were measured using a direct enzyme immunoassay (EIA, CJM006), which was physiologically (ACTH challenge) and analytically validated (parallelism, accuracy and precision tests) for the species under study. The results indicated that the average GCM concentration was lower in the competition group (33.43 ± 22.09 ng/g) as compared to the control group (70.09 ± 29.45 ng/g; P = 0.01). However, concentrations spiked significantly on competition day (D0: 38.29 ± 26.12 ng/g) as compared to the rest day (D-3: 28.64 ± 17.86  ng/g; P = 0.02), suggesting acute stress response. Given the elevated GCM levels observed during competitions, further research is necessary to confirm the welfare of these birds under competition conditions and to explore the long-term effects of such stressors.