Reproduction and population levels of Peruvian Guano Birds, 1980 to 1986

The three species of guano birds, guanay cormorant (Phalacrocorax bougainvillii), Peruvian booby (Sula variegate), and Peruvian pelican (Pelecanus occidentalis thagus), depend mainly on the Peruvian anchovy (Engraulis ringens) for sustenance. A naturally occurring limitation on the population size of these birds is the oceanographic phenomenon known as “El Nino”. The industrialization of the anchovy fishery during the 1960s and 1970s has also affected seabird populations: The annual extraction of huge volumes offish has decreased the availability of food for the guano birds, causing large population fluctuations and considerable changes in the relative abundance of the birds. Because of its great intensity and duration, the 1982–1983 El Nino caused high avian mortality, depressing populations to levels from which they have not yet recovered.