How Many Species of Birds Have Existed?

Abstract

The present world avifauna is composed of about 8650 species. During the Pleistocene and late Tertiary the avifauna was larger, with about 11,600 species living at any given time. Before the adoption of the granivorous habit in the mid-Tertiary, the avifauna was smaller, with an estimated 10,200 contemporaneous species. The Crataceous avifauna consisted mainly of aquatic birds and contained about 1000 contemporaneous species. In the late Jurassic the avifauna was negligible, with probably not more than 100 species existing at any one time. The average longevity of avian species is considered to be the equivalent of the time needed to replace half the fauna. Based on the rate of extinction in Pleistocene faunas, the average longevity is estimated at about 500,000 years. Multiplying the number of contemporaneous species by the duration of a given epoch and dividing by the average species longevity gives the number of species evolved during that epoch. Addition of the epochal totals gives the number of species that have existed since the origin of class Aves. This is estimated to be about 1,684,000 species. The described living and fossil birds total about one-half of one percent of those potentially knowable.