HOW MANY BIRDS ARE THERE

Attempts to assess the magnitude of global biodiversity have focused o n estimating species richness. However, this is but one component of b iodiversity, and others, such as numbers of individuals or biomass, ar e at least as poorly known and just as important to quantify. Here, we use a variety of methods to estimate the global number of individuals for a single taxon, birds. The different methods yield surprisingly c onsistent estimates of a global bird population of between 200 billion and 400 billion individuals (1 billion = 10(9)). We discuss some of t he implications of this figure.