3-4 months. Roosters generally need to grow up to 4 months before crowing. Some chickens grew up eating feed in the greenhouse and ingested more hormones, so they developed earlier and may start crowing at 2.5 months or 3 months. Yanjin Black-bone Chicken is a specialty of Yanjin County, Zhaotong City, Yunnan Province, and a geographical indication of national agricultural products. Yanjin black-bone chicken is named after its origin and main producing area in Yanjin County, Yunnan Province.