Why are alcids unique

Alcids (or auks) fill a similar ecological niche in the northern hemisphere as penguins do in the southern hemisphere, except alcids can fly - and can fly long distances. The top photo is of a mixed group of Rhinoceros Auklets and Common Murres in flight over Monterey Bay in February, some having flown thousands of miles from Alaska to reach that rich pelagic wintering locale.

To quote Nettleship (1996), alcids are "a highly specialized and ecologically diverse group of marine, wing-propelled pursuit-diving birds." Many live at high northern latitudes - like this group of Atlantic Puffins and Razorbills (left) on Machias Seal Island, Canada - where their fat well-insulated bodies and comical appearances add to the feeling that they recall "northern penguins." Like penguins, though, some species reach tropical latitudes.