Convection and thermoregulation in two Antarctic seabirds

Abstract

1. Metabolism and heat transfer were measured at different wind speeds (V) and ambient temperatures (Ta) in Adelie penguins (Pygoscelis adeliae) and blue-eyed shags (Phalacrocorax atriceps). Five age classes of penguins (adults, fledglings, and 1-, 2-, and 3-kg downy chicks) and three age classes of shags (adults and 2- and 3-kg chicks) were studied. 2. In penguins, rates of oxygen consumption (\(\dot V_{{\text{O}}_{\text{2}} } \)) in the absence of forced convection increased with decreasingTa in downy chicks. The\(\dot V_{{\text{O}}_{\text{2}} } \) of fledglings and adults increased marginally at −20°C. Lower critical temperatures (T1c) were approximately 15–20°C for 1-kg chicks, −5°C for 2-kg chicks, and −10°C for 3-kg chicks, fledglings, and adults. In shags,T1c was approximately 0°C for all age classes, and\(\dot V_{{\text{O}}_{\text{2}} } \) increased substantially at −20°C. 3. Wind speeds of 3–6m·s−1 elicited significantly increased\(\dot V_{{\text{O}}_{\text{2}} } \) in all age classes of both species at −20°C. The largest increases were observed in adult and fledgling penguins (averaging 190% compared to\(\dot V_{{\text{O}}_{\text{2}} } \) in the absence of forced convection). At 0°C,V had smaller but still significant effects in shags, but in penguins wind had little effect on\(\dot V_{{\text{O}}_{\text{2}} } \) at thisTa. The\(\dot V_{{\text{O}}_{\text{2}} } \) of all age classes of both species was independent ofV at of 20°C. 4. The response of thermal conductance (C) to changingV andTa resembled that for\(\dot V_{{\text{O}}_{\text{2}} } \). TheC of fledglings and adults of both species increased rapidly with increasingV at lowTa but was independent ofV at highTa. In shags, minimalC did not differ significantly among age classes, but in penguinsC was highest in 1-kg chicks and lowest in adults. 5. In both penguins and shags, the responses of\(\dot V_{{\text{O}}_{\text{2}} } \) andC to changingV were similar in 3-kg downy chicks and adults, indicating that convection effects on down and feather plumages do not differ.