Wilson's Warbler

The Wilson's Warbler (Cardellina pusilla) is a diminutive and sprightly New World warbler, characterized by its vibrant yellow underparts and olive-green upperparts. The adult male is distinguished by a striking black cap, which is either reduced or absent in the female, depending on the subspecies.

Identification Tips

When attempting to identify this species, look for the male's black crown patch and the bird's overall green and yellow plumage. The Wilson's Warbler has rounded wings and a long, slim tail. Size-wise, it ranges from 10 to 12 cm in length, with a wingspan of 14–17 cm. The western race, C. p. chryseola, is greener above and more vividly colored than the eastern, nominate race.

Habitat

Wilson's Warblers are found in fairly open woodlands with an abundance of undergrowth, shrubs, and thickets, particularly in moist areas near streams, ponds, bogs, and wet clearings.

Distribution

This species breeds across Canada and south through the western United States. During the winter months, it migrates to Mexico and continues through much of Central America. It is an exceedingly rare vagrant to western Europe.

Behaviour

Wilson's Warblers are active foragers, often seen flitting rapidly through shrubs, close to the ground, and occasionally in taller trees during the winter. They may exhibit tail twitching or wing flicking while feeding.

Song & Calls

The song of the Wilson's Warbler is a series of chattering, loud descending notes. Its call is a distinctive flat "chuff."

Breeding

Breeding begins in early March for west coast populations and can extend into August in the northern range. The female primarily constructs the cup nest, which is often hidden in moss or sedges at the base of shrubs. Clutch size ranges from 2 to 7 eggs, which are creamy or off-white with fine reddish spots. The young are altricial, hatching at 11–15 days and fledging at 8–13 days.

Similar Species

The Wilson's Warbler can be confused with the Yellow Warbler, but the latter can be differentiated by its shape, yellow wing markings, and yellow tail spots.

Diet and Feeding

Primarily an insectivore, the Wilson's Warbler feeds on insects gleaned from leaves and twigs or captured in flight. Its diet includes beetles, bees, and caterpillars, and occasionally it consumes berries.

Conservation Status

The IUCN Red List classifies the Wilson's Warbler as Least Concern. However, the chryseola subspecies has experienced a sharp decline in the 21st century due to habitat loss from development in its wintering grounds in Mexico.