Storm-petrels are thrush-sized seabirds that rarely approach land except to nest, and usually at night, so most people never see them.  They spend most of their time over deep oceanic waters inconspicuously flitting around their larger and better-known relatives, such as albatrosses and shearwaters.  Storm-petrels comprise two of the four families known as “tubenoses”—named for the tubular nostril-like structures on the tops of their bills which apparently provide two functions crucial to their maritime lifestyles: secreting excess ocean salt and enabling the birds to detect subtle scents and follow them to ephemerally productive foraging areas scattered far and wide across the open ocean.

All storm-petrels are roughly the same size and shape, and all were traditionally regarded as belonging to a single family, which seemed to be the only conceivable approach to classifying this outwardly uniform group.  Advances in genetic analytical methods fundamentally changed this understanding, however, revealing that the northern- and southern-breeding species are not closely related, so they are now classified as two families: the Hydrobatidae (northern) and the Oceanitidae (southern).  One interpretation of the DNA evidence concludes that the southern storm-petrels were the first lineage of tubenoses to diverge from the rest and are more closely related to albatrosses than to the northern storm-petrels—but this remains unsettled.