Physiological response of <i>Pygoscelis</i> penguins in a rapidly changing region

Abstract We evaluated the physiological condition of the Pygoscelis penguins at Isla 25 de Mayo/King George Island (Antarctica Peninsula). Samples were collected from adults and chicks of Adélie ( Pygoscelis adeliae , n = 20 each), gentoo ( Pygoscelis papua , n = 20 chicks and n = 24 adults) and chinstrap penguins ( Pygoscelis antarcticus , n = 18 each). We analysed haematological and biochemical parameters as indicators of health, immune response and nutrition. Gentoo penguin chicks exhibited higher haematocrits, indicating development linked to erythropoiesis and reticulocyte release from bone marrow or signalling dehydration related to fasting periods in chicks. Adélie penguins had increased total leukocyte counts, basophils and eosinophils, whereas gentoo penguins showed elevated heterophils and decreased lymphocytes, resulting in a higher heterophil/lymphocyte ratio stress index, possibly due to the impact of human activities. Chinstrap penguins from a remote area exhibited the lowest heterophil/lymphocyte ratio values. Adélie penguins showed more erythrocytic nuclear abnormalities, indicating sensitivity to environmental deterioration due to human impacts. The biochemical results were less consistent; Adélie penguins had higher cholesterol, whereas gentoo penguins had elevated triglycerides. Gentoo penguins showed dietary adaptability based on prey availability in this area. Our findings highlight the vulnerability of Adélie penguins and contribute to a 20 year physiological monitoring dataset for Antarctic penguins, which will aid future comparative studies.