THE FREQUENCY-DISTRIBUTION OF BIRD BODY WEIGHTS - AQUATIC AND TERRESTRIAL SPECIES

The frequency distribution of the log-transformed body-weights of the world's bird species is right-skewed, The reasons for this skew are un known. Aquatic bird species are on average heavier and have a less ske wed distribution of weights than would be expected if they were a rand om sample from the overall weight distribution. Conversely, terrestria l species on average weigh less, and their weight distribution is more skewed, This is partly a phylogenetic effect; species of aquatic and terrestrial birds belong to different families. These differences sugg est factors which may be important determinants of the overall weight distribution of birds.