Visual Signal Design, Perception and Mating Success in Bowerbirds

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

Visual Signal Design, Perception, and Mating Success in Bowerbirds John A. Endler Sexual Selection can result in males with remarkably complex secondary sexual traits, and may be important in speciation because mating preferences drives it. Most studies of sexual selection have concentrated on the signal content rather than the design. By analogy with radio or TV transmission, animal signals consist of a carrier (e.g. a color pattern) or signal design and the content (e.g. advertising direct or genetic benefits to the female or her offspring of mating with a particular male). Although very general predictions about the evolution of signals can be made considering only signal content or genetics these models do not allow specific predictions about the details of the signals, nor do they predict how the carrier should evolve. For visual signals (color patterns), a knowledge of microhabitat, time, weather, viewing conditions during signaling and eye properties allows specific predictions about which colors and patterns should be used under specific conditions. This approach allows specific predictions about animal signals, regardless of signal content. In most animals, the visual signaler has little or no control over the appearance of its signals. In bowerbirds (Ptilonorhynchidae) males construct and decorate bowers, which are used visually to attract mate. The fact that the bower is constructed rather than fixed means that the visual signal (bird + bower) is constrained only by what the birds can find, and makes it possible to examine the consequences of experimental manipulation of the signals in unrestrained animals in the field, and thus test hypotheses about visual contrast, perception, and fitness in natural populations. This project will study the design of Bowerbird visual signals using current models of early visual processing. Experiments will investigate: (1) whether or not visual contrast is maximized by bower design and location relative to diurnal patterns of light, shade and ambient light spectra; (2) the choice of objects in relation to Passerine bird vision, and whether or not male bowerbirds select objects which maximize the visual contrast to female bowerbirds of the bower and bird visual signal; and (3) whether bower visual contrast perceived by the birds successfully predicts mating. These approaches will be integrated in order to understand the function, design and evolution of visual signals. The study will also illuminate some aspects of the basis for color preferences. This will be the first fully integrated study of visual contrast, microhabitat choice, and function of a visual signal and should provide new insights into the direction of evolution of visual signals.