Formerly in the genus Sterna, now various tropical pelagic terns and the Aleutian Tern, have been found to be more closely related to each other, and only distantly related to true Sterna terns. This is based on molecular data, and this is why now they are classified into the genus Onychoprion. There are two tropical Onychoprion in much of the New World, the Sooty and the Bridled Tern, and often the two are found together. Both are found in both Pacific and Atlantic oceans, although Bridled is more common in the Atlantic. In much of the Pacific Ocean a closely related tern, the Grey-backed Tern, replaces the Bridled. As its name suggest it has a bridled pattern, this is a white strap that goes around the neck of the bird, dividing the blackish cap from the brownish-grey upperparts. Below this tern is entirely white, and the face is accented by a white forehead and short white backward pointing eyebrows. This tern is colonial, nesting in tropical islets sometimes side by side with the larger and blackish relative, the Sooty Tern. The Bridled Tern becomes pelagic in the non-breeding season and in the Atlantic is particularly attached to floating mats of Sargassum Weed, and often is found perched on the weed, or on other floating detritus within the mats. A few Bridled Terns remain well to the north, in the latitude of Florida in winter, but most move farther south. How northern and more southern populations interrelate is still unknown, as breeding seasons of southern and northern populations are quite different. This is a tropical tern, associated with warm ocean water temperatures, but one vagrant record stands out. One individual was sighted, and eventually collected way down south off Cape Horn! The person who first sighted and identified this ridiculously stray individual was none other than Roger Tory Peterson.