El Niño / Southern Oscillation and North American Land Birds by Steven

606 Introduction From the end of 1982 through the first few months of 1983, in the Galápagos Islands of the eastern tropical Pacific Ocean, there was a huge mortality of nesting seabirds. For example, populations of the Galápagos Penguin (Spheniscus mendiculus) and Flightless Cormorant (Phalacrocorax harrisi) declined by 49% and 77%, respectively (Valle and Coulter 1987). Other species, such as Blue-footed Booby, Lesser Frigatebird, Magnificent Frigatebird, and Brown Pelican, also experienced high mortalities. Many individuals of these and other species managed to survive by migrating away from the Galápagos Islands, abandoning their young birds to starve to death. At first, this dramatic incident puzzled ornithologists. However, it quickly became evident that this massive mortality and migration of seabirds was due to the occurrence of an exceptionally strong warming of the waters in the eastern tropical Pacific Ocean. Such a pattern of oceanic warming was a clear signal of the occurrence of an El Niño. Measurements of the sea surface temperature (hereafter, SST) subsequently revealed that the 1982–1983 El Niño was the strongest El Niño up to that time during the 20th century. The ocean water in this region is normally cold due to the upwelling of deep water from far below the ocean surface. Accompanying this cold water is an abundance of nutrients that supports a diverse ecosystem. During an El Niño, this cold water upwelling is suppressed. As a result, there is a large reduction in available nutrients, leading to a collapse in the populations of the fish and other marine species that seabirds normally prey upon. Twenty years ago, El Niño was not only unknown to the public; even most atmospheric scientists were unaware of this phenomenon. The apparent intensity and dramatic impact of the 1982–1983 El Niño on worldwide weather, causing destructive floods and devastating droughts on a global scale, brought this phenomenon to the attention of atmospheric scientists and the general population alike throughout the world. In North America, perhaps the most striking influence of this El Niño was the rash of severe storms that battered the coast of California. Over the past two decades, since the 1982–1983 event, there have been many interesting scientific studies on the impact of El Niño on North American birds. Most of these studies have focused on seabirds. Presumably this emphasis on seabirds stems from the observation that during El Niño the SST in a narrow strip along much of the west W E AT H E R A N D C L I M AT E