|Range of I. galbula Breeding range Wintering range|
The Baltimore oriole (Icterus galbula) is a small icterid blackbird common in eastern North America as a migratory breeding bird. It received its name from the resemblance of the male's colors to those on the coat-of-arms of Lord Baltimore. Observations of interbreeding between the Baltimore oriole and the western Bullock's oriole, Icterus bullockii, led to both being classified as a single species, called the northern oriole, from 1973 to 1995. Research by James Rising, a professor of zoology at the University of Toronto, and others showed that the two birds actually did not interbreed significantly.
Like all New World orioles, this species is named after an unrelated, physically similar family found in the Old World: the Oriolidae. "Oriole" ultimately derives from Latin aureolus, "golden". The genus name Icterus is from Ancient Greek ikteros, a yellow bird, usually taken to be the Eurasian golden oriole, the sight of which was thought to cure jaundice. The specific galbula is the Latin name for a yellow bird, again usually assumed to be the golden oriole.
This medium-sized passerine measures 17-22 cm (6.7-8.7 in) in length and spans 23-32 cm (9.1-12.6 in) across the wings. Their build is typical of icterids, as they have a sturdy body, a longish tail, fairly long legs and a thick, pointed bill. The body weight averages 33.8 g (1.19 oz), with a range of weights from 22.3 to 42 g (0.79 to 1.48 oz). The male oriole is slightly larger than the female, although the size dimorphism is minimal by icterid standards. Adults always have white bars on the wings. The adult male is orange on the underparts shoulder patch and rump, with some birds appearing a very deep flaming orange and others appearing yellowish-orange. All of the rest of the male's plumage is black. The adult female is yellow-brown on the upper parts with darker wings, and dull orange-yellow on the breast and belly. The juvenile oriole is similar-looking to the female, with males taking until the fall of their second year to reach adult plumage.
Baltimore orioles are found in the Nearctic in summer, primarily the eastern United States. They breed from Minnesota to Maine and south to central Mississippi and Alabama and northern Georgia. They migrate to winter in the Neotropics as far north as Mexico and sometimes the southern coast of the United States, but predominantly in Central America and northern South America. Some areas of the southern United States may retain orioles all winter if they have feeders that appeal to them. The range of this bird overlaps with that of the similar Bullock's oriole in the Midwest, and the two species were once considered to be conspecific under the name northern oriole because they form fertile hybrids. The Baltimore oriole is a rare vagrant to Western Europe.
Baltimore orioles are often found high up in large, leafy deciduous trees, but do not generally reside in deep forests. The species has been found in summer and migration in open woodland, forest edge, and partially wooded wetlands or stands of trees along rivers. They are very adaptable and can breed in a variety of secondary habitats. In recent times, they are often found in orchards, farmland, urban parks and suburban landscapes as long as they retain woodlots. In Mexico, they winter in flowering canopy trees, often over shade coffee plantations.
The male sings a loud flutey whistle, with a buzzy, bold quality, a familiar sound in much of the eastern United States. The male typically sings from the tree canopy, often giving away its location before being sighted.
Male Baltimore oriole singing
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Baltimore orioles are basically solitary outside their mating season. The species is generally considered monogamous, although evidence suggests that extra-pair copulation is reasonably common. In the spring, males establish a territory then display to females by singing and chattering while hopping from perch to perch in front of them. Males also give a bow display, bowing with wings lowered and tail fanned. Depending on their receptiveness, the females may ignore these displays or sing and give calls or a wing-quiver display in response. The wing-quiver display involves leaning forward, often with tail partly fanned, and fluttering or quivering slightly lowered wings.
The Baltimore oriole's nest is built by the female. It is a tightly woven pouch located on the end of a branch, consisting of any plant or animal materials available, hanging down on the underside. Trees such as elms, cottonwoods, maples, willows or apples are regularly selected, with the nest usually located around 7 to 9 m (23 to 30 ft) above the ground. The female lays three to seven eggs, with the norm being around four. The eggs are pale gray to bluish white, measuring 2.3 cm × 1.6 cm (0.91 in × 0.63 in) on average. The incubation period is 12 to 14 days. Once the nestlings hatch, they are fed by regurgitation by both parents and brooded by the female for two weeks. After this the young start to fledge, becoming largely independent shortly thereafter. If the eggs, young, or nest are destroyed, the oriole is unable to lay a replacement clutch.
Predation is a common source of mortality, typically also occurring with eggs, nestlings and fledgings. Common predators at Baltimore oriole nests can include common grackles, American crows, Blue Jays, black-billed magpies, tree squirrels and domestic cats, which most commonly capture newly fledged orioles or adults engaged in brooding behavior. Rapacious birds commonly prey on both young and fully-grown orioles, the most prolific being the eastern screech owl and Cooper's and sharp-shinned hawks. Somewhat larger rapacious birds also sometimes opportunistically predate the oriole, including peregrine falcons, great horned owls, and barn owls, while merlins may do so while orioles are migrating.
The record lifespan for a wild bird was 11 years and 7 months, with captive orioles living up to 14 years.
Baltimore orioles forage in trees and shrubs, also making short flights to catch insects. They acrobatically clamber, hover and hang among foliage as they comb high branches. They mainly eat insects, berries and nectar, and are often seen sipping at hummingbird feeders. Their favored prey is perhaps the forest tent caterpillar moth, which they typically eat in their larval stage, and can be a nuisance species if not naturally regulated by predation. The larvae caterpillar are beaten against a branch until their protective hairs are skinned off before being eaten. Unlike American robins and many other fruit-eating birds, Baltimore orioles seem to prefer only ripe, dark-colored fruit. Orioles seek out the darkest mulberries, the reddest cherries, and the deepest-purple grapes, and will ignore green grapes and yellow cherries even if they are ripe. Baltimore orioles sometimes use their bills in an unusual way, called "gaping": they stab the closed bill into soft fruits, then open their mouths to cut a juicy swath from which they drink with their tongues. During spring and fall, nectar, fruit and other sugary foods are readily converted into fat, which supplies energy for migration.
Many people now attract Baltimore orioles to their backyards with oriole feeders. Such feeders contain essentially the same food as hummingbird feeders, but are designed for orioles, and are orange instead of red and have larger perches. Baltimore orioles are also fond of halved oranges, grape jelly and, in their winter quarters, the red arils of gumbo-limbo (Bursera simaruba). If they discover a well-kept feeder, orioles lead their young there.