Why do animals hybridize?

Animal hybridization is increasingly recognized as common and evolutionarily important, but the role of behavior in promoting hybridization events is not well understood. Understanding the behavioral causes of hybridization requires understanding the ecological, demographic, and phenotypic influences on mate choice in hybridizing taxa. Here, I review how these influences on mate choice can contribute to hybridization by (1) circumventing (female) choice, (2) bringing formerly isolated species into sympatry, (3) masking cues important for mate recognition, (4) altering the traits or preferences involved in mate recognition, or (5) altering the costs and benefits of mate choice. In particular, hybridization in response to either high direct costs of mate choice or high direct benefits of heterospecific mating may be widespread, a possibility that awaits further testing. Adopting a mate choice perspective to the study of hybridization challenges the assumption of hybrids as reproductive "mistakes" and allows for functional explanations regarding the occurrence and maintenance of hybridization. As evidence of the prevalence and evolutionary importance of animal hybridization accumulates, investigations into the role of behavior will be increasingly important for our understanding of diversification and for conservation applications.