Studying geographic variation in the rate of hybridization between closely related species could provide a useful window to understand the evolution of reproductive isolation. Reinforcement theory predicts greater prezygotic isolation in areas of prolonged contact between recently diverged species than in areas of recent contact, which implies that old contact zones would be dominated by parental phenotypes with few hybrids (bimodal hybrid zones) whereas recent contact zones would be characterized by hybrid swarms (unimodal hybrid...