page_title: Northern storm petrel
section_title: Morphology and flight
hierarchical_section_title: Northern storm petrel / Morphology and flight
context_page_description: Northern storm petrels are seabirds in the family Hydrobatidae, part of the order Procellariiformes. The family was once lumped with the similar austral storm petrels in the combined storm petrels, but have been split, as they were not closely related. These smallest of seabirds feed on planktonic crustaceans and small fish picked from the surface, typically while hovering. Their flight is fluttering and sometimes bat-like.
  The northern storm petrels are found in the Northern Hemisphere, although some species around the Equator dip into the south. They are strictly pelagic, coming to land only when breeding. In the case of most species, little is known of their behaviour and distribution at sea, where they can be hard to find and harder to identify. They are colonial nesters, displaying strong philopatry to their natal colonies and nesting sites. Most species nest in crevices or burrows, and all but one species attend the breeding colonies nocturnally. Pairs form long-term, monogamous bonds and share incubation and chick-feeding duties. Like many species of seabirds, nesting is highly protracted, with incubation taking up to 50 days and fledging another 70 days after that.
context_section_description: Northern storm petrels are the smallest of all the seabirds, ranging in size from 13–25 cm in length.  The Hydrobatidae have longer wings than the austral storm petrels, forked or wedge-shaped tails, and shorter legs. The legs of all storm petrels are proportionally longer than those of other Procellariiformes, but they are very weak and unable to support the bird's weight for more than a few steps.
  All but two of the Hydrobatidae are mostly dark in colour with varying amounts of white on the rump. Two species have different plumage entirely,  Hornby's storm petrel, which has white undersides and facial markings, and the fork-tailed storm petrel, which has pale grey plumage. This is a notoriously difficult group to identify at sea. Onley and Scofield (2007) state that much published information is incorrect, and that photographs in the major seabird books and websites are frequently incorrectly ascribed as to species. They also consider that several national bird lists include species that have been incorrectly identified or have been accepted on inadequate evidence.
  Storm petrels use a variety of techniques to aid flight. Most species  occasionally feed by surface pattering, holding and moving their feet on the water's surface while holding steady above the water. They remain stationary by hovering with rapid fluttering or  using the wind to anchor themselves in place. This method of feeding flight is more commonly used by Oceanitidae storm petrels, however. Northern storm petrels also use dynamic soaring, gliding across wave fronts gaining energy from the vertical wind gradient.
caption: Unusually for the Hydrobatidae, the fork-tailed storm petrel has an all-grey plumage.
exif: {"Image Orientation": "Horizontal (normal)", "Image XResolution": "300", "Image YResolution": "300", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS Windows", "Image DateTime": "2006:04:04 14:16:51", "Image ExifOffset": "164", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "302", "Thumbnail JPEGInterchangeFormatLength": "5587", "EXIF ColorSpace": "Uncalibrated", "EXIF ExifImageWidth": "3175", "EXIF ExifImageLength": "2110"}