Bullock's Orioles breed in riparian and open woodlands, including urban parks. They favor areas where the trees are large and spaced well apart or in isolated clumps. They often nest in sycamores, cottonwoods, willows, deciduous oaks, madrones, and large mesquite trees. Live oaks, pecans, orchard trees, saltcedar and occasionally conifers are also used. This bird gravitates toward larger trees than those used by the Orchard Oriole. They use similar open woodland habitats during migration and winter, and may also be found in pine, pine-oak, or fir forests. Back to top
Bullock's Orioles eat insects and other arthropods, as well as fruit and nectar. They glean insects from leaves, branches and trunks; they also pluck insects from spiderwebs or from the air, and take ripe fruit from bushes and trees. Bullock's Orioles use a method called "gaping" to extract juice from fruit, and also sometimes from tough-skinned caterpillars. Thrusting their closed bills through the skin and into the flesh of the fruit or animal, they then pry their bills open inside and lap up the pooling juices with their brushy tongues. Sometimes these orioles skin caterpillar prey by hitting it repeatedly on a branch. Before eating honeybees, they extract and drop the stinger. Common prey insects include caterpillars, grasshoppers, and crickets. The birds also take beetles, ants, bugs, scale insects, stinkbugs, leafhoppers, treehoppers, and small spiders. Rarely, they eat small lizards. They take nectar from agaves, introduced eucalyptus, and other flowers. Commonly consumed fruits include blackberries, raspberries, cherries, and figs. Nestlings are fed crickets, stick insects, camel crickets, cicadas, moth and butterfly pupae, earwigs, ants, and crane flies. Back to top
The female selects the nest site, typically 10 to 25 feet above the ground in an isolated tree or at the edge of a woodland, commonly near water. The nest is usually suspended from the ends of flexible branches to discourage predators. It is not necessarily situated within the male's advertising territory. Several other active nests may be close by.
The female usually weaves the nest, but the male may assist, with one partner working on the inside and other outside, bringing nest material. The project can take up to 15 days to complete. The nest is gourd-shaped and neatly woven from fibers such as hair, twine, grasses, or wool. It's lined with soft materials such as feathers or the "cotton" from cottonwoods or willows. Nest depth varies, averaging a bit less than 4 inches and ranging up to 15 inches. On average, Bullock's Oriole nests are deeper and wider than those of the Baltimore Oriole, though the opening diameter is smaller.
|Clutch Size:||3-7 eggs|
|Egg Length:||0.8-1.1 in (2-2.8 cm)|
|Egg Width:||0.6-0.7 in (1.4-1.8 cm)|
|Egg Description:||Pale bluish or grayish white, splotched with purplish brown lines.|
|Condition at Hatching:||Helpless with long, sparse white down.|
Bullock's Orioles glean and probe in trees for insects and nectar, often hanging upside down for extended periods. They make short hops from branch to branch, sometimes flying to the ground to nab insects. Their flight is strong and direct. During migration, they congregate in small, loose, mixed-gender flocks. The male performs a bowing courtship display, hopping from branch to branch and bowing to the female every second or so—all the while singing loudly and exposing his colorful plumage. During nest-building and border disputes, the female may display with quivering wings, holding her body in a roughly horizontal position. Rival males face off at territorial borders and chase each other through tree branches. Bullock's Orioles remain paired up throughout the breeding season but may take new mates in later years. Both members of a pair guard the nest and may mob squirrels, crows, jays, and other predators. Females tend to sing near the nest site, while males often sing elsewhere. Back to top
Bullock's Oriole are widespread and common, but populations declined by approximately 0.6 % per year for a cumulative decline of about 27% between 1966 and 2019, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 7.4 million and rates them 11 out of 20 on the Continental Concern Score, indicating a species of relatively low conservation concern. This oriole is affected by loss of riparian habitat from the depletion of groundwater due to irrigation, and likely by pesticide use through direct contamination and loss of insect prey.Back to top
Dunne, P. (2006). Pete Dunne's essential field guide companion. Houghton Mifflin Harcourt, New York, USA.
Flood, Nancy J., Claudia L. Schlueter, Matthew W. Reudink, Peter Pyle, Michael A. Patten, James D. Rising and Pamela L. Williams. (2016). Bullock's Oriole (Icterus bullockii), version 3.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.
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Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.
Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2019). The North American Breeding Bird Survey, Results and Analysis 1966–2019. Version 2.07.2019. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.
Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.