Wilson's Storm-Petrel or Least Storm-Petrel?

General appearance

The Wilson's Storm-Petrel is a small, delicate seabird known for its dark plumage and contrasting pale rump. It possesses a sooty-black body with a lighter brown shade on the wings, and its undersides are similarly dark. A distinctive white band spans across the rump, providing a stark contrast to its otherwise dusky appearance. The tail is square-shaped, and the bird's slender legs extend well beyond the tail feathers as it hovers above the ocean surface. It measures approximately 16-18 cm in length and has a wingspan of about 38-42 cm.

Male vs female

Wilson's Storm-Petrels exhibit little to no sexual dimorphism, meaning that males and females appear almost identical in size and plumage coloration. There may be subtle differences in size or minor variations in feather tone, but these are not easily discernible in the field without close examination or during the breeding season.

Juvenile

Juvenile Wilson's Storm-Petrels resemble their adult counterparts closely but may be slightly duller in overall plumage coloration. The white band on their rump is less defined and may appear more off-white compared to the brilliant white seen in adults. As they mature, the clarity and contrast of their plumage increase, matching that of the adults. Over time, as juveniles reach full maturity, any variations in their appearance become less pronounced.

Primary Habitat

The Wilson's Storm-Petrel primarily inhabits the offshore marine environments of the Southern Hemisphere. They are frequently found in the Southern Ocean, especially near the Antarctic Convergence. Their habitat includes cold, nutrient-rich waters where they spend much of their time feeding on plankton and small marine organisms, showcasing a preference for polar and subpolar climates.

Additional Range

While primarily southern, they occasionally venture into the Northern Hemisphere during the non-breeding season. Wilson's Storm-Petrels have been observed in temperate oceans worldwide, and some even forage near coastlines during migration. Their adaptability allows them to exploit a variety of marine habitats beyond their usual range.

Natural Diet

Wilson's Storm-Petrel primarily sustains itself on a diet comprising small marine organisms. This seabird flies over the ocean, expertly dipping to catch plankton, crustaceans, and small fish close to the water's surface. They are particularly fond of tiny krill and copepods, which abound in the colder waters of their nesting areas. During feeding, they employ a characteristic "pattering" technique, appearing to dance on the water's surface as they pick at prey. Seasonal variations are noticeable as they follow the abundance of prey, often feeding near swarms of marine life, which vary depending on local ocean currents and temperatures.

Bird Feeders

Wilson's Storm-Petrel is not known to frequent bird feeders, and there are no typical offerings they would consume at such stations. These birds are strictly oceanic and rarely venture near land except for nesting purposes. They do not have a specific affinity for any non-marine feed items like seeds or suet. To encounter Wilson's Storm-Petrel, bird enthusiasts should consider oceanic expeditions or pelagic birdwatching tours rather than attempting to attract them with backyard feeders. Such excursions provide glimpses of these fascinating birds in their natural feeding habitats, dancing across the waves in search of their oceanic diet.