Historically, studies of sensory systems of birds have focused on hearing and sight. The chemical senses, chemesthesis (irritation and pain), olfaction (smell), and gustation (taste) had been only modestly studied, and primarily focused on neural responses and behavioral studies. In this chapter we focus on irritation and smell. Taste is covered elsewhere in this volume. The study of chemical senses in birds has lagged relative to other avian sensory modalities (i.e., vision and hearing) owing to the nature of the stimuli. Volatile cues, at lower concentrations for olfaction, and higher concentrations for chemesthesis, emanate from a chaotic environment often making it difficult to precisely know what is in the signal and at what concentration, let alone the potential myriads of signals that are present and need processing. However, recent advances in genetics and molecular biology have allowed for a more detailed mechanistic focus on the independent and interactive role performance of the chemical senses. We now understand that birds have a well-developed functional sense of smell as evidenced by multiple research areas from the past 60 years. The same is true of our understanding of chemical cues as irritants. Herein we review the neural organization responsible for mediating odor and chemesthetic stimuli; receptor mechanisms; integration of sensory stimuli in a behavioral, ecological, and evolutionary context; and, possible applied uses resulting from a better understanding of how these sensory modalities function.
