| Summary: | application/pdf Penguins are outstanding divers. Particularly intriguing is the observation that they seem to dive on inspiration, which contributes to increasing oxygen stores but which increases their buoyancy. It has been concluded that buoyancy is a major factor in determining the energetics of shallow diving birds and there is a positive correlation between estimated air volume in the body (respiratory system and feathers) and the maximum depth in the dive of free-ranging penguins. However, it is not known whether the variation in the total air volume is caused by the variation in the air volume in the respiratory system or in plumage. In the present study, underwater weights of restrained Adelie penguins Pygoscelis adeliae (n=27 birds) were continuously measured in a experimental tank. The birds lost much air from their feathers within 1-2 min of submergence. The maximum weights in the water were used to calculate the minimum air volumes that diving birds are expected to have in their body. These volumes were compared with estimated air volumes from two free-ranging Adelie penguins. Most estimated values of the free-ranging birds were larger than values from the restrained birds, which indicates that variation in the former air volume is likely caused by the variation in the air in the respiratory system. Penguins seem to adjust the volume of air inhaled to the maximum depths of their dives. departmental bulletin paper
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