There are 13 races of this bird. Only a biopsy can determine whether a suspicious area is cancerous. Heavy sun exposure can cause cancer of the lip. Lunch time A common yellowthroat takes time out to enjoy a quick snack. Its diet consists mostly of insects, which are either caught during flight or on the ground. Common Yellowthroat has a jerky flight and will dart around especially when males are scolding an intruder.