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Early movement between
the Pacific and and the Atlantic probably happened to the south
(since there was no northern opening to the Atlantic), later movements
across the Arctic Sea. The extant auks are broken up into 2 main
groups, the puffins (subfamily Fraterculini) and auklets (subfamiliy
Aethiini), and the Uria guillemots (subfamily Alcini), murrelets
and guillemots (subfamilies Cepphini and Brachyrampphini). Compared
to other families of seabirds, there are no genera with many species
(such as the genus Larus in the gulls, which has 47 species).
This is probably a product of the limited range of the family
(the most limited of any seabird family), and the periods of glacial
advance and retreat that has kept the populations on the move.
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Today, as in
thge past, the auks are restricted to cooler northern waters.
Their ability to spread further south is restricted as their prey
hunting method, pursuit diving, becomes less efficient in warmer
waters. The speed at which small fish (which along with krill
are the auk's principal food items) can swim doubles as the temperature
increases from 5°C to 15°C, with no coresponding increase
in speed for the bird. The southernmost auks, in California and
Mexico, can survive there because of cold upwellings. The current
paucity of auks in the Atlantic (6 species), compared to the Pacific
(19-20 species) is considered to be because of extinctions to
the Atlantic auks, the fossil records shows there were many more
species in the Atlantic during the Pliocene. Auks also tend to
be restricted to continental shelf waters and breed on few oceanic
islands.
The Above Images From U.S. Fish and Wildlife Service
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