Comments: Formerly included in Larus but separated on the basis of genetic data (Pons et al., 2005) that indicate that the genus would be paraphyletic if the following species were included: C. philadelphia, C. cirrocephalus, and C. ridibundus (AOU, 2008). Considered conspecific with with South American L. maculipennis by some authors. Regarded as monotypic by most authorities. See Nikula (1993) for information on hybridization with other gull species. Formerly named "common black-headed gull" (AOU, 1995).