Double-crested Cormorants can be seen migrating through or to New York City. Relatively scarce around the five boroughs during the winter, they are replaced during the cold months by Great Cormorants. Several of the islands that dot New York Harbor or the Long Island Sound north of the city are home to large colonies of breeding double-cresteds. This bird is one of several species that are part of the New York City Audubon Society's Harbor Heron project. As a defense mechanism cormorant nestings will vomit on a perceived threat, so approach a nest colony forewarned.