Storm petrels (Hydrobatidae) are a group of tubenose seabirds that include species such as the European storm petrel, Wilson's storm petrel, Leach's storm petrel, New Zealand storm petrel, white-faced storm petrel and others.
Storm petrels spend most of their time at sea and journey back to land only to breed. They nest in colonies and most species return time and again to breed in the same location that they were born. Storm petrel pairs are monogamous and form long term bonds. They share in the responsibilities of incubating and feeding their young.
Storm petrels are the smallest seabirds. They range in size from about 5 to 10 inches in length. The two subgroups of storm petrels (the Oceanitinae and the Hydrobatinae) differ in their general body shape. The Oceanitinae have short wings, an elongated head, long legs and a square tail. In contrast, the Hydrobatinae have comparatively longer wings, a rounder head, short legs and a tail that is either forked or wedge-shaped.
Storm petrels also employ two different methods of flying. The Hydrobatinae tend to use dynamic soaring, a method of flight that involves gliding along the air above wave fronts to gather energy from the perpendicular wind gradient. The Oceanitinae tend to use slope soaring, a method of flight that involves turning into the wind to gain lift and height (much like an airplane taking off into a headwind). The bird then glides back down to the water surface and repeats the process.
Just as the two storm petrel groups differ in body shape and flying methods, they also differ in plumage pattern coloration. The plumage of Oceanitinae species is a classic example of counter shading, with a dark feathers covering the head, back and upper parts and white feathers covering the throat, belly and undersides of the wings. Most Hydrobatinae are dark overall with a white patch on their rump. There are some exceptions to these generalizations though. The Hornby's storm petrel for example has white facial feathers and the fork-tailed storm petrel is mostly a pale grey color.
Storm petrels are a cosmopolitan group of birds, they can be found throughout the most of the world's oceans and seas. They do not occur in the Arctic Ocean. Some species of storm petrels are migratory. The Wilson's storm petrel, for example, travels from Antarctica where it breeds to the waters of the north Pacific and Atlantic oceans. In contrast, some species such as the Tristram's storm petrel and the grey-backed storm petrel remains in the same range year-round and does not migrate.
Although the diet of storm petrels is poorly documented, it is generally believed that most species feed on crustaceans, small fish and molluscs. Most species feed on the wing while flying over open ocean. They generally capture prey while hovering above the water's surface (they rarely dive into the water in pursuit of a meal). Some species catch prey while using a behavior known as surface pattering in which they hover in one place using a rapid fluttering of their wings while touching or "pattering" their feet on the water as they grasp prey just beneath the surface.
Storm petrels are Procellariiformes, a group of seabirds also known as the tubenoses (for their tubular nostrils). In addition to storm petrels, the Procellariiformes also include albatrosses, shearwaters and diving petrels. There are two groups of storm petrels, the Oceanitinae and the Hydrobatinae. These groups are roughly distinguished by the range they occupy. The Oceanitinae occur mostly in the southern hemisphere while the Hydrobatinae occur mostly in the northern hemisphere (although there are a few exceptions to these rules).