Bullock's oriole (Icterus bullockiorum, also known as Icterus bullockii) is a small New World blackbird. At one time, this species and the Baltimore oriole were considered to be a single species, the northern oriole. This bird is named after William Bullock, an English amateur naturalist.

Description

Bullock's orioles are sexually dimorphic, with males being more brightly colored than females. In addition, adult males tend to be slightly larger and heavier than females.

Measurements:

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Adults have a pointed bill with a straight culmen. In adult males, the tail is long, square, and jet black. All exposed skin is black, as are the claws and bill, though the base of the lower mandible lightens to bluish-gray.

Adult males are characterized by contrasting yellow-orange and black plumage, a black throat patch, and a white wing patch on the wing coverts. The underparts, breast, and face are orange or yellow; by contrast, the back, wings, and tail are black. A black line extends from each eye to the black crown. Adult females, by contrast, have gray-brown upperparts, duller yellow on the breast and underparts, and an olive crown. Some females may also have a dark throat patch, similar to (but less extensive than) the one found in adult males; in all cases, females lack the black eye-line present in adult males. Females with throat patches are thought to be older individuals.

Following the general pattern observed among icterids, the overall plumage pattern seen in immature male Bullock's orioles closely resembles that seen in adult females. Juveniles resemble adult females, but have darker wings, fresh wing coverts, and a pink or whitish bill. Sexual dimorphism is not obvious in juveniles.

Reproduction

thumb|left|Bullock's oriole nests near San Jose, California

Bullock's orioles are seasonally monogamous. The breeding season typically lasts from May until July. The exact timing of the beginning of the breeding season tends to vary geographically; in general, breeding begins later in the northernmost and westernmost portions of its geographic range. Mated pairs of Bullock's orioles cooperate to weave deep, pendant baskets in which are deposited between three and six eggs, though females tend to do much of the work. The nest is woven of plant fibers, primarily bark and fine grass fiber, though animal hair is also commonly used. The nest is lined with down, hair, and moss.

Both males and females rear the young and defend the nest from predators and nest parasites.

Bullock's orioles and Baltimore orioles typically hybridize in the Midwest, where their geographic ranges overlap.

Communication

Both males and females sing. While males have a sweeter voice, females tend to be more prolific singers. This bird's song is similar to that of the Baltimore oriole, but faster and somewhat more harsh.

Distribution

Bullock's orioles are native to western North America, though <!-- according to Jaramillo (1999) --> they are sometimes found as vagrants in the eastern half of the continent.

For a time Bullock's orioles were considered conspecific with Baltimore orioles, but breeding data, later followed by data on molt timing and DNA, showed that Bullock's orioles are a distinct species.

References

  • Bullock's oriole Species Account - Cornell Lab of Ornithology
  • Bullock's oriole - Encyclopedia of Life
  • Bullock's oriole - Icterus bullockii - USGS Patuxent Bird Identification InfoCenter
  • Bullock's oriole - BirdHouses101.com