The Distribution of Body Sizes of the World's Bird Species

Data for more than 6000 species are used to determine the form of the frequency distribution of the body masses of all extant bird species. The distribution of known masses is strongly right-skewed, even on logarithmic axes, and the median bird mass is 37.6 grammes. We present evidence that this right-hand skew is a real property of the body mass distribution, and not the result of a biased sample of bird masses