[order] Passeriformes | [family] Parulidae | [latin] Wilsonia pusilla | [UK] Wilsons Warbler | [FR] Paruline à calotte noire | [DE] Mönchswaldsänger | [ES] Chipe de Coronilla Negra | [IT] Parula di Wilson | [NL] Wilson-zanger

Wilson-zanger determination

copyright: Richard Garrigues

About 10% smaller than Hooded Warbler with proportionately shorter, finer bill; close in size to Yellow Warbler. Quite small, animated, willow-loving Nearctic wood warbler, with bright olive-green upperparts and lemon-yellow underparts; male has black cap; no white in tail.

Breeds almost throughout Nearctic climatic zones, from Arctic tundra and montane valleys and slopes in Alaska, and up to nearly 500 m in southern California. Favours moist open shrubbery, including willow and dwarf birch, especially by streams, ponds, and bogs. On migration, more tolerant of drier situations.

Breeds in North America from northern Alaska east to Newfoundland and south throughout most of Canada, extending in western USA to California and New Mexico, in eastern USA to northern Minnesota, northern Vermont, and Maine. Accidental. Britain: male, Rame Head (Cornwall), October 1985.

Wilson's Warblers eat insects and other small invertebrates. They also sometimes eat berries.

This species has a large range, with an estimated global Extent of Occurrence of 7,900,000 km². It has a large global population estimated to be 36,000,000 individuals (Rich et al. 2003). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]

Wilson's Warblers are primarily monogamous, although some are polygynous, and high rates of extra-pair copulations have been observed. Pacific Lowland populations lay fewer eggs, raise fewer young, and have higher rates of monogamy than populations in the mountains. Lowland populations nest in shrubs, unlike their ground-nesting highland relatives. The female selects the nest site, either sunken in a patch of moss or sedge, or in a low shrub or vine. She builds a bulky open cup of leaves, grass, and moss, lined with grass and hair. The female incubates 2 to 7 eggs for 11 to 13 days, and broods the young for the first few days after they hatch. Both parents feed the young, which leave the nest 9 to 11 days after hatching. The parents continue to feed the young for up to 25 days after they fledge.

Migratory, moving at least 800 km (most birds over 2500 km) between summer and winter ranges. Winter range (Mexico and southern Texas south to Panama) very limited in comparison with breeding range; highest numbers in Mexico. Migration on broad front in both seasons, mainly west of Appalachians, with most birds skirting Gulf of Mexico to west rather than overflying it; uncommon to rare in south-east states and West Indies. A few vagrant records July-September in Arctic Canada and Alaska, on islands in Bering Sea, and in Greenland.