The development of homeothermy in common eider ducklings (Somateria mollissima).

Oxygen consumption (VO2), body temperature (TB) and electric muscle activity (EMG) were measured at varying ambient temperatures (TA) in common eider ducklings from the eggs pipped to 1 day after hatching. Eggs at pipping and ducklings still wet from hatching doubled their VO2 at TA = 2-4 degrees C compared with TA = 27 degrees C, but were unable to maintain constant TB. Increased EMG activity was recorded from ducklings 30 min after hatching. Artificially dried 1-h-old ducklings maintained normal TB (39.0-40.5) for at least 90 min at TA = 2 degrees C. Ducklings older than 24 h maintained homeothermy even when the pelt was artificially wetted. Oxygen consumption at thermoneutrality increased about 50% from hatching to 12 h of age. The specific thermal conductance of ducklings at different ages indicates that the youngest ducklings maintain homeothermy by having a cold periphery in addition to pelt insulation and increased VO2, while ducklings older than 12 h rely on pelt insulation and increased VO2 only.