ECOGEOGRAPHIC VARIATION AND INTROGRESSION IN AN AVIAN VISUAL SIGNAL: THE CREST OF THE STELLER'S JAY, CYANOCITTA STELLERI

Abstract

In animals with a strongly developed visual sense, particular behavior patterns are often associated with specialization in form and color of the structures that serve as visual signals. Birds of paradise have their almost unbelievable plumes, hummingbirds their fiery iridescent gorgets, and waterfowl an amazing variety of plumage patterns, all prominent in displays. The evolution of these specializations is often simply stated as resulting from advantages in attracting and stimulating females, or from advantages in the outcome of aggressive encounters. As is often the case with simple explanations, however, there is far more to be considered. The problems of why particular specializations evolved in certain groups, and what factors influence the kind, extent, and limit of their specialization are less often studied. This paper is concerned with factors influencing the degree of specialization in a visual signal, the crest of the Steller's Jay (Cyanocitta stelleri).