A study published in the journal Science details avian evolution and may change the way birds are classified. The study, conducted by the Field Museum here in Chicago, shows that nightjars and hummingbirds have a lot in common and grebes and loons--often thought to be related--don't have much in common. Here is a paragraph from an online report:
"Similarly, distinctive lifestyles (such as nocturnal, raptorial and pelagic, i.e., living on the ocean or open seas) evolved several times. For example, contrary to conventional thinking, colorful, daytime hummingbirds evolved from drab nocturnal nightjars; falcons are not closely related to hawks and eagles; and tropicbirds (white, swift-flying ocean birds) are not closely related to pelicans and other waterbirds."