The role of bare parts in avian signaling

Abstract

ABSTRACT Avian plumage has captivated scientists and the public alike for generations and has been a fundamental study system for research into signal evolution. By contrast, relatively little attention has been paid to avian bare parts such as exposed skin, bills, feet, and combs, despite considerable variation in structure and coloration within and between species. To better understand the potential signaling role of bare parts, we conducted a comprehensive literature search that returned 321 published studies. In reviewing these studies, we found that (1) bare-part color is widely distributed taxonomically and is produced by diverse mechanisms; (2) many bare parts are likely to be dynamic, honest signals of current condition or status and can also reflect genetic makeup and early developmental conditions; and (3) bare parts can function as pluripotent social signals, mediating interactions between competitors, mates, and kin. Differences between bare parts and plumage in phenology and information conte...