Comparative corticosterone responses to capture stress in sympatric Antarctic penguins

Adverse environmental stimuli activate the hypothalamic-pituitary-adrenal axis, releasing corticosterone (CORT), the primary stress hormone in birds. This hormone facilitates adaptive responses to acute stressors, ensuring immediate survival but potentially compromising other vital functions when chronically elevated. In penguins, particularly those of the genusPygoscelis, there is a striking lack of comparative data on stress physiology, especially for chicks, despite their ecological importance as bioindicators of Antarctic ecosystem change. Understanding species and age-specific stress responses is essential given their shared habitat, contrasting behavioral traits, and increasing exposure to climate change-related stressors. This study investigated the effects of capture and restraint on CORT concentrations in three sympatric penguin species: P. adeliae(Adélie),P. papua(Gentoo), andP. antarcticus(Chinstrap) nesting on King George Island, Antarctica. Blood samples were collected from adults and chicks of P. adeliae (n = 25 and n = 8) and P. antarcticus (n = 18 and n = 10), and from adults of P. papua (n = 18) at baseline (within 5 min of capture, CORT₀) and after restraint for 30, 45, or 60 min (CORT₃₀, CORT₄₅, CORT₆₀). Opportunistic urofecal samples (n = 36) were also analyzed from adults of the three species to compare excreted hormone levels with circulating one. All species showed a significant and non-linear increase in blood CORT following capture. Concentrations peaked at 30 min post-capture in P. adeliaeand P. Papua which showed a pattern of initial increase followed by a temporary decline and secondary rise in corticosterone levels,whereas P. antarcticushad a more gradual and progressive increase over time peaking at 45 min. Interestingly,P. antarcticuschicks exhibited higher CORT₀ concentrations than adults, potentially reflecting greater reactivity to stress, whereasP. adeliaechicks showed values similar to adults, consistent with a maturing stress response. Urofecal CORT concentrations did not significantly differ among species but were consistently higher than baseline blood levels, likely reflecting integrated stress over time. This is the first study to compare baseline and stress-induced CORT concentrations across all threePygoscelisspecies, to measure CORT in adults and chicks ofP. antarcticus, and to analyze Pygoscelis populations from King George Island. By filling critical gaps in penguin stress physiology, these findings contribute to understanding interspecific and developmental variation in endocrine responses, confirm that capture and restraint significantly alter corticosterone levels and highlight the need for careful consideration of capture and handling procedures in wildlife research and conservation practices.