Estimating the mass of the Great Auk (Pinguinus impennis) and its egg

The body mass and egg mass of the Great Auk Pinguinus impennis were never measured before the bird was driven to extinction in 1844. Previous studies conducted before 1990 used data from related species to estimate the mass of an adult bird at 4500–5000 g, and the fresh mass of its egg as 327–372 g. In the present study, we use a larger dataset of measurements from extant alcids, and statistical methods that control for the effects of phylogeny, to provide new estimates for those traits. The presumed body mass of the Great Auk was initially derived from a hearsay report from the 18th century, and then supported by subsequent comparative analyses based on skeletal measurements. Our new best estimates from currently available data show that the Great Auk's body mass was probably closer to 3560 g and its fresh egg mass was about 350 g. This new body mass estimate is the average of predictions from independent regressions of body mass on (1) tibiotarsus and femur lengths (3441 g) and (2) egg volume (3681 g). We calculated the Great Auk's fresh egg mass from a regression of fresh egg mass on egg volume in the extant alcids. Providing more accurate estimates of the body and egg mass of Great Auk can inform speculation about the developmental mode, ecology and life history of this iconic, extinct species.