Condors - giant birds of the Andes

  A high mountain ledge amid the steep crags of the Peruvian Andes is home to the condor. One of the world's biggest birds, it has the lowest natural breeding rate of any bird. This is partly because each pair has only one egg at a time and takes two years to raise the chick. It is also because, for many, their food supply fluctuates considerably.

  Condors are vultures, feeding on carrion. As they glide and soar on air currents, they can spot a corpse or a dying animal a long distance away. Under normal conditions the condors living in the hot, dry Andean foothills in the north of Peru have a fairly meagre existence, and few breed. But every five years or so the devastation caused by storms along the South American Pacific coast as a result of El Niño enormously increases their food supply.

  Wildlife and farm animals suffer disease caused by a sudden proliferation of flies, mosquitoes and parasites. Weak and ageing animals do not survive the bad weather. The glut of corpses brings a time of plenty for the condors - a time when all the breeding pairs may raise young. A year after the 1982-3 El Niño storms, the ledges were packed with year-old birds. In the years between the storms, most birds do not breed.

  Their lengthy breeding cycle means that condors are at great risk, especially those inland in the High Andes. They cannot recover their numbers after poisoning by ranchers or if there is no El Niño for several years. Condors in the coastal mountains feed on seabird chicks and eggs and are less dependent on the periodic gluts of carrion after storms.