Guano, the first commercial fertilizer used in any large quantity, is not a bird manure, but a new substance formed by its decomposition under extremely dry climatic conditions. Its formation requires the presence of a multitude of certain species of birds perennially nesting and raising another multitude within a comparatively small area. And, as the guano birds are fish eaters, their presence depends upon a proportionate abundance of small fish within easy range. The cold Benguela Current of the southwest African coast presents conditions favorable to guano-producing birds.