Clark's Grebe
Aechmophorous clarkii
These Clark's Grebes were observed from Cesar Chavez Park in Berkeley, CA on March 17, 2009. The Clark's Grebes have their eyes surrounded by white feathers, whereas the very similar looking Western Grebes have their eyes surrounded by dark feathers. For many years Clark's Grebes and Western Grebes were considered variants of the same species. However, studies have shown that the two types do not interbreed even when in the same location. The definition of species that is used most often in science, called the Biological Species Concept, is a group of organisms (birds) in a natural population that interbreed freely within the group but not across groups.