Wild breeding raptors may sometimes accept and raise nestlings other than their own. Under natural conditions, nestling raptors do not normally find themselves in foreign nests; therefore, no selective pressure exists in this group to favor the development of parental ability to recognize their own young. Breeding raptors thus may care for any nestling in their nest (Postupalsky 1975). Taking advantage of this biological trait, wildlife managers and conservationists have used cross-fostering of raptor nestlings among different species, particularly for endangered species (Bird et al. 1985). For example, Meyburg and Heydt (1973) used this technique to increase the reproductive output of both Eastern Imperial Eagle (Aquila heliaca) and Lesser Spotted Eagle (Clanga pomarina), with the latter effort involving cross-fostering by another species.
The Chaco Eagle (Buteogallus coronatus) is endemic to South America. It inhabits dry forests and savannas across Argentina,...