Once we found evidence of hybridization between rustica and gutturalis in Jiuquan, we needed to map the width of the hybrid zone. We set out on our zigzagging plan: after 3 nights of catching birds in Jiuquan, we hopped the high-speed train to Zhangye. Again, we found excellent stretches of old courtyard-style houses, and again, we found birds that looked like both rustica and gutturalis nesting close to each other. The birds in Zhangye were early in their breeding cycle- only a few had begun laying eggs, and most were still building their nests. Luckily they were sleeping on their nests, and we managed a big sample size over 3 nights of work.