The alterations of phenotypic traits (morphology, endocrine physiology, and behavior) in response to predictable environmental cues across life‐history stages in seasonally breeding birds enable successful culmination of reproduction. The present study elucidated the plasticity of the hypothalamic–pituitary–adrenal (HPA) axis in a subtropical free‐living finch, Amandava amandava amandava, and suggests the crucial role of the baseline corticosterone (CORT) to coordinate energetic readiness across life‐history stages. Birds were captured monthly from an area (25.1337° N 82.5644° E) in Uttar Pradesh, India, from June 2014 to May 2015. Only male birds were included in this study corresponding to different life‐history stages (6/life‐history stage; 2/month): pre‐breeding (June–August), breeding (September–November), post‐breeding (December–February), and quiescent phases (March–May). The pituitary expression of adrenocorticotropic hormone (ACTH), adrenal interrenal cell morphometry, and plasma level of the CORT showed varied patterns across life‐history stages. The density and immunointensity of the ACTH‐immunoreactive corticotropes and the interrenal cell number increased along with the significant plasma CORT elevation during the breeding cycle (both pre‐breeding and breeding phases). CORT might facilitate the energy demand for the display of sexual behavior (nest‐building, courtship), testicular recrudescence, and foraging of food for offspring during the breeding cycle. On the contrary, plasma CORT decrease in the post‐breeding and quiescent phases might enable the bird to molt avoiding the protein catabolic effect of the hormone. Given the complexity involved in the study of baseline CORT in free‐living birds, more studies are needed to better understand the crucial role of the HPA axis in the modulation of life‐history stages in this and other subtropical avian species.
