Vibrational Signals in Multimodal Courtship Displays of Birds

Abstract

Birds often combine vocalization and body movements for communication with other individuals, but our knowledge of this multimodal communication is primarily limited to the vocal and visual signals. Since birds often stay and communicate upon a substrate that seems to be efficient in the transmission of substrate-borne vibrations (e.g., courtship bobbing on a branch), it is rather surprising that vibrational signals have been almost completely overlooked in past studies of their communication. In the blue-capped cordon-bleu (Uraeginthus cyanocephalus), a socially monogamous songbird, both sexes perform courtship displays that are characterized by singing and simultaneous visual displays. We previously found that their courtship bobbing includes rapid tap dance-like behavior, which is assumed to produce vibrations that propagate through the perch and non-vocal sounds in addition to visual signals. In this chapter, we introduce our previous findings of this multimodal courtship display as well as quantitative analyses of substrate-borne vibrations produced by cordon-bleus. We will also discuss the potential of vibrational signals for bird communication by describing their possible functions and evolutionary scenarios. We believe that investigating vibrational communication in birds can provide fruitful insights into the role of vibrations in the evolution of complex communication systems.