Wilson's Storm-Petrel

Overview

Wilson's Storm-Petrel is one of the smallest seabirds and among the most numerous, breeding in vast colonies on subantarctic islands and Antarctica before dispersing widely across the world's oceans. Its small size, sooty coloring, and habit of pattering its feet on the water while feeding make it a distinctive sight far offshore.

Despite its diminutive size, it undertakes long-distance movements between breeding and non-breeding areas, and its feathers are correspondingly built for sustained, energy-efficient flight over open water.

A Wilson's Storm-Petrel feather is small and delicate compared to almost any other seabird likely to be encountered.

• Body feathers: Sooty black to sooty brown overall, with a band of white feathers across the rump that stands out sharply against the dark plumage.
• Flight feathers: Primaries and secondaries are blackish and relatively short and rounded for the bird's size, without strong barring.
• Compared to European Storm-Petrel: Wilson's feathers are similar in color but the species is slightly larger overall, and Wilson's shows long legs with yellow-webbed feet that project noticeably beyond the tail in flight, useful when a whole bird or wing is being examined rather than a loose feather.
• Compared to Leach's Storm-Petrel: Leach's is larger with a more forked tail and a paler, more contrasting pale bar on the upperwing; Wilson's wing feathers are more uniformly dark.

Adults are almost entirely sooty black to sooty brown, relieved only by the crisp white rump band and a pale diagonal bar across the upperwing coverts. Sexes look alike. Juveniles closely resemble adults. The molt cycle is completed mostly in the non-breeding range away from the colony, allowing feather replacement without interrupting the demands of breeding.

Wilson's Storm-Petrels breed on Antarctic and subantarctic islands and coastlines, nesting in burrows or rock crevices, then migrate widely across the Atlantic, Pacific, and Indian Oceans during the austral winter, reaching well into the Northern Hemisphere in some regions. They are highly pelagic, spending virtually all non-breeding time far from land over open ocean.

This species feeds by fluttering low over the water and pattering its feet on the surface while picking small planktonic prey, fish fragments, and oily material from the sea surface, sometimes gathering in loose feeding flocks around fishing vessels. Nesting occurs in burrows or crevices in dense colonies, with adults visiting nests only at night to avoid predators, and a single egg is laid per season. Calls are soft chattering or churring notes given mainly underground at the nest.