Visual signals for individual identification: The silent "song" of Ruffs

Breeding male Ruffs (Philomachus pugnax) appear to communicate individual i dentity through extreme variation in coloration and pattern of their plumag es. If plumage variation evolved to provide sufficient information. to sign al individual identity, we might expect different plumage components to var y independently. We find that variation in four plumage characteristics is largely independent. Previous studies produced conflicting answers about pl umage-component independence, perhaps because they failed to separate two g enetically distinct behavioral categories of males, which differ in plumage types, in their analysis. We propose that using plumage variation to signa l individual identity, rather than voice (used by most other bird species) was favored by lengthy daytime male display in open habitats in close proxi mity to receivers. However, signaling associated with the unique dimorphism in this species' male mating behavior might also have influenced the evolu tion of extraordinary plumage diversity in this species.