Red-throated Loon Gavia stellata
Version: 2.0 — Published April 16, 2020
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It has been claimed that breeders on the Arctic islands of Spitsbergen and Franz Josef Land are lighter and grayer dorsally (67, 68). Such differences are the result of individual variation, however, in that not all individuals that breed on those islands show the characters, yet individuals that breed elsewhere do (44, 62). As such, the name applied to birds of those islands, Gavia stellata squamata (69), becomes a junior synonym of Gavia stellata (Pontoppidan, 1763). Additional synonyms are Colymbus lumme Gunnerus, 1761; Colymbus borealis Brünnich, 1764; Colymbus septentrionalis Linnaeus, 1766; and Colymbus mulleri Brehm, 1826.
The is no morphological variation that can be ascribed to geography (see Systematics History).
On the basis of gross morphology, the small family Gaviidae—there are only 5 species of loons (or divers) worldwide—was long considered to be phylogenetically close to Podicipedidae, the grebes (70, 71), yet recent genetic evidence has consistently found Podicipedidae and Gaviidae are not at all closely related. Instead, Podicipedidae appears sister to Phoencopteridae (flamingos), while Gaviidae appears to be sister to a large clade of waterbirds, which includes the Sphenisciformes (penguins) and Procellariformes (albatrosses, shearwaters, and petrels), as well as the Ciconiiformes (storks), Suliformes (frigatebirds, boobies and gannets, anhingas, and cormorants), and Pelecaniformes (pelicans, herons and egrets, and ibises and spoonbills) (72, 73, 74, 75).
Like that of Common Loon (see Evers et al ). Earliest loons were extinct genus Colymboides from Eocene to early Miocene (79, 80). Genus Gavia appeared during Miocene (81), and in 3 size classes by early Pliocene (82). Early Oligocene fossil of species metzleri tentatively placed in the genus Colymboides represents the first remains of an early Tertiary loon with direct evidence of specialization toward piscivorous diet and marine habitat use (83). Late Oligocene fossil of Colymboides suggests occurrence in warmer regions than extant Gaviidae (84).