What is "whyos"

The Whyos, a collection of the various post- Civil War street gangs of New York City, was the city's dominant street gang during the late 19th century. The gang controlled most of Manhattan from the late 1860s until the early 1890s, when the Monk Eastman Gang defeated the last of the Whyos. The name came from the gang's cry, which sounded like a bird or owl calling, "Why-oh!"