Larus smithsonianus

Formerly (AOU 1983, 1998) Larus argentatus was considered conspecific with L. vegae, L. smithsonianus, and extralimital L. mongolicus Sushkin, 1925 [Mongolian Gull], but separated from L. smithsonianus based on phylogenetic analyses that suggest that these species are not sister taxa (Crochet et al. 2002, 2003; Liebers et al. 2004; Pons et al. 2005; Sternkopf et al. 2010; Sonsthagen et al. 2016) and differences in adult and juvenal plumages (Adriaens and Mactavish 2004, Lonergan and Mullarney 2004). Separated from L. vegae based on phylogenetic results that indicate that these species are not sister taxa (Sonsthagen et al. 2016), and phenotypic differences (Yésou 2002). Species L. vegae and L. mongolicus, the latter of which may be more closely related to L. cachinnans Pallas, 1811 [Caspian Gull] (e.g., Olsen and Larsson 2003, Sonsthagen et al. 2016), are separated based on vocal, plumage, behavioral, and genetic differences (Yésou 2001, Moores 2017, Weseloh et al. 2020, Cerný and Natale 2022, Billerman and Rasmussen 2025) (AOS 2025).