The western bluebird (Sialia mexicana) is a small North American thrush.

Taxonomy

The western bluebird was formally described by the English naturalist William Swainson in 1832 and given the binomial name Sialia mexicana.

Six subspecies are recognized:

  • S. m. occidentalis Townsend, JK, 1837 – southwest Canada to north Baja California (northwest Mexico)
  • S. m. bairdi Ridgway, 1894 – interior west USA to Sonora and Chihuahua (northwest Mexico)
  • S. m. jacoti Phillips, AR, 1991 – south central USA and northeast Mexico
  • S. m. amabilis Moore, RT, 1939 – northcentral Mexico
  • S. m. nelsoni Phillips, AR, 1991 – central Mexico
  • S. m. mexicana Swainson, 1832 – south central Mexico

Description

The western bluebird is a small stocky bird with a length of . The adult male is bright blue on top and on the throat with an orange breast and sides, a brownish patch on back, and a gray belly and undertail coverts. The adult female has a duller blue body, wings, and tail, a gray throat, a dull orange breast, and a gray belly and undertail coverts. Both sexes have a thin straight bill with a fairly short tail. Immature birds have duller colors than the adults, and have spots on their chest and back.

Their calling consists of the mating songs which sound like "cheer," "chur-chur," and "chup." This helps male western bluebirds find the females easily in condensed forest. The males use these calls to tell competing males that the territory belongs to them. They have been found to enjoy more success with nest boxes than in natural cavities. They started egg-laying earlier, had higher nesting success and lower predation rates, and fledged more young in boxes than in cavities, but they did not have larger clutches of eggs. The eggs are commonly two to eight per clutch, with average size . Eggs are oval in shape with a smooth and glossy shell. They are pale blue to bluish-white and sometimes white in color. Nestlings remain in a nest about 19 to 22 days before fledging. In a good year, the parents can rear two broods, with four to six eggs per clutch. According to genetic studies, 45% of western bluebirds' nests carried young that were not offspring of the male partner. In addition, they help their parents raise a new brood after their own nest fails.

Food and feeding

The western bluebird pounces on the ground when looking for food, such as worms and berries. It also flies to catch aerial prey, like insects, when available. The western bluebird consumes water from nearby streams and commonly use bird baths.