Aethia
Aethia is a genus of four small (85–300g) auklets endemic to the North Pacific Ocean, Bering Sea and Sea of Okhotsk and among some of North America's most abundant seabirds.[1] The relationships between the four true auklets remains unclear. Auklets are threatened by invasive species such as Arctic foxes (Alopex lagopus) and Norway rats (Rattus norvegicus) because of their high degree of coloniality and crevice-nesting.
The genus Aethia occurs only in the North Pacific and adjacent waters, mainly in the Bering Sea region. Along with Cassin's auklet (Ptychoramphus aleuticus) they comprise the monophyletic tribe Aethinii. Molecular work has not yet resolved the relationship between the Aethia auklets, but the group is a sister group to Cassin's auklet, which is, in turn, a sister group to the Fraterculine auks (puffins and rhinoceros auklet).[2]
The genus Aethia did not enter into widespread use until the 1960s.[3] Initially, the auklets were placed in Alca,[4] but later reorganized into genera including: Simorhynchus,[5] Phaleris and Cyclorhynchus.[1] Cyclorhynchus is still occasionally used for the parakeet auklet.
The first undisputed auk fossils are from the middle Miocene (15 million years ago).[1] The first Aethia fossils date from the late Miocene (8–13 million years ago)[6] and the four extant species likely diverged rapidly about 5 million years ago.[7]
There are one or two fossil species which lived in the area of today's California during the Late Miocene: Aethia rossmoori Howard, 1968 (Monterrey Formation of Orange County), and an undescribed taxon tentatively placed in this genus. From the Pliocene there are Aethia barnesi N. A. Smith, 2013 (San Mateo Formation of San Diego County, California, and Aethia storeri N. A. Smith, 2013 (San Mateo Formation of San Diego County, California.
Censusing breeding auklets can be difficult because they nest in hidden crevices.[8] At present, population estimates are:[1]
