Impacts of the 1982-1983 El Nino on Population Dynamics of Andean Condors in Peru

Abstract

We studied how the environmental perturbations associated with the 1982-1983 El Niiio phenomenon affected the population dynamics of Andean condors (Vultur gryphus) in three areas of Peru. For at least four years prior to the 1982-1983 El Niiio, nearly all adult condors in a coastal population and an Andean foothill population refrained from breeding; whereas condors in a high-elevation population appeared to be breeding once every other year. The severe environmental disruptions of the 1982-1983 El Niiio caused the food supply for the coastal population of condors to decrease, while the food supply for the foothill population increased 17 fold. The food supply for the high-elevation population was little affected by El Niiio because climatic changes in the area were inconsequential. In response to the increase in food, almost all condors in the foothill population bred in the months following El Niiio. No condors in the coastal population bred after El Niiio, and breeding of condors in the high-elevation population was presumably unaffected. If they can reproduce only during the unpredictable El Niiio years, coastal and foothill condor populations may barely be able to maintain their numbers without ingress from more regularly breeding populations. The rate of breeding in these desert-dwelling condors seems to be the lowest recorded among birds. THE PHENOMENON OF EL NiNo is associated with the periodic occurrence and persistence of unusual oceanographic and climatic conditions along the coast of Peru and Ecuador (Cane 1983, Philander 1983, Rasmusson & Wallace 1983). Although most reports of the ecological consequences of El Ninio have focussed on its detrimental effects on animal movements, reproductive cycles, and survival (e.g., Murphy 1936, Barber & Chavey 1983, Karr 1984, Schreiber & Schreiber 1984), certain species should benefit. The food supply for carrion feeders, for example, should improve during an El Niiio event as stress resulting from environmental changes increases mortality rates in species on which they feed. We studied three populations of Andean condors (V. gryphus) in Peru before and after the 1982-1983 El Nifio and here report how the environmental disruptions associated with that El Ninio affected the population dynamics of this large carrion feeder. We found evidence that individuals in coastaland foothill-dwelling populations of condors breed very infrequently, if at all, in the drought years between El Nifio events; they seem to breed only in response to the flush of carrion resulting from environmental changes in El Ninio years. We discuss the implications of this irregular breeding pattern on the dynamics of these condor populations, and we contrast them with populations of condors high in the Andes where the environmental consequences of El Ninio are less pronounced. STUDY SITES We studied condors from May 1980 to August 1982 and from March 1984 to August 1984 in three areas of Peru: the Cerro Illescas on the Sechura Peninsula, the Olmos and Naupe regions in the western Andean foothills, and Pampa Galeras in the high Andes. The Cerro Illescas is a unique geological formation on Peru's northern coast. Located on the tip of the Sechura Peninsula (6?S, 80?W), this isolated mountain range is bordered on three sides by the Pacific Ocean and separated from the Andes Mountains to the east by over 150 km of sparsely vegetated desert. The mountains cover an area approximately 40 x 20 km and reach a maximum elevation of 480 m. From this central high point, dry steep-walled canyons radiate to the periphery of the hills and provide roosting and nesting ledges for condors. Our second study area was 150 km east of the Cerro Illescas in the western foothills of the Andes near the towns of Olmos (6.00?S, 79.46?W) and Naupe (5.350S, 79.46?W), which are 75 km apart. In these foothills that rise to about 1000 m, steep brushy slopes and precipitous escarpments isolate the roosting and nesting sites of condors from the activities of people living on the desert grasslands below. Our third study site was Pampa Galeras (14.400S, 74.23?W), a high-elevation puna grassland at an altitude of 41 00 m. This 5 12,000-ha, grassy plateau is occasionally transected by deep canyons that provide roosting and nesting ledges for condors.