Date of this Version
Nebraska Bird Review (June 1992) 60(2): 70.
The role of polymorphism in bird plumage has been debated. One theory is that prey species become familiar with the common plumages of raptors and avoid them, but are unlikely to recognize unusual plumages as indicating dangerous birds (Clarke 1969). In other words, the rare plumage acts as a sort of disguise. This theory assumes that prey learn the appearance of their predators, but since prey that encounter hawks often end up dead, the opportunity for learning may be limited (Arnason 1978). An incident at Bellevue, Nebraska supports the hypothesis that an unusual color phase can act as a disguise.