Wilson’s Storm-petrels are named after the Scottish-American ornithologist, Alexander Wilson. They are small dark brownish birds (16-19 cm in length, 38-42 cm wingspan) with short, rounded wings and long legs, with a pale wing patch and a white shaped band on their rump. When flying, their legs will trail behind their rounded or square tail. Wilson’s Storm-petrels have external tubular nostrils, from which they excrete the salt that accumulates in their body tissues and air in odor detection for locating prey. Wilson’s Storm-petrels are best suited a marine or pelagic distribution, as they have limited walking ability on land.
Can be Confused With
Many of the storm-petrels are easily confused with one another, due to their small size and similar appearances. Wilson’s Storm-petrels are often mistaken to be Leach’s or Band-rumped Storm-petrels. Wilson’s Storm-petrels are much smaller in size than each of these species, but size can often be a difficult indicator in the field. The flight patterns of each can be one feature used to distinguish them. Leach’s Storm-petrels have an erratic flight, Band-rumped Storm-petrels fly much like a shearwater, and Wilson’s Storm-petrels have a fluttery light with deep wingbeats. Wilson’s Storm-petrels can be confused with the Wedge-rumped Storm-petrel on the western coast of the United States, but distinctive differences are apparent in the banding pattern on their tails. Wedge-rumped Storm-petrels have a deep ‘V’ in the white band on their tail, which causes the tail to look white with black corners. Wilson’s Storm-petrels have a more rounded band on their tail.
Wilson’s Storm-petrels have a large range, considering their small size, and are pelagic outside of the breeding season. Their breeding grounds are located in the Antarctic, during the Southern Hemisphere’s summer months (Northern Hemisphere’s winter). The rest of the year, they can be found in all oceans, more common in the North Atlantic than the North Pacific during the Southern Hemisphere’s winter.
Ecology and Behavior
Wilson’s Storm-petrels breed on the coastlines and nearby islands of Antarctica. They lay a single white egg. Nests are built in colonies in rock crevices or in shallow burrows in the ground. Due to predation by gulls and skuas in their breeding grounds, Wilson’s Storm-petrels are slightly nocturnal throughout the breeding season. Year to year, Wilson’s Storm-petrels display strong site fidelity to nesting grounds.
Feeding and Prey
Wilson’s Storm-petrels feed primarily on plankton and other small organisms, such as protozoa, bacteria, macroalgae, fish eggs, larval fish and crustacean larvae. They are “surface seizers” when feeding, as they hover at the surface pattering their feet on the surface, which causes them to look like they are walking on the water. They capture prey by using their bills while hovering right above the surface of the water.
Threats and Status
Wilson’s Storm-petrels are considered to be of “least concern” according to the IUCN Red List. They are not believed to be approaching thresholds for population decline, as their population is estimated to be around 6 million, and they are considered to be one of the most abundant species of birds.