Scientific Name: Icterus galbula
The Northern Oriole
(Information for this species page was gathered in part by William Dailey for Biology 220M at Penn State New Kensington in Spring 2006)
The northern oriole (Icterus galbula) is a composite species combining the eastern “Baltimore oriole” and the western “Bullock’s oriole.” Adults of this species are 7 to 8 inches long and have a wingspan of 9 to 12 inches. They weigh 1 to 1.5 ounces. Using the common bird size descriptor for a North American species, “they are slightly smaller and a bit more slender than a robin.” Males are much more distinctively colored than the females and have orange breasts, abdomens, and rumps, black wings with white bars, and a black head. Females and immature males have olive brown backs and heads (possibly with some black), yellow to orange breasts and abdomens, and brownish wings with white bars.
Northern orioles spend the spring and summer seasons in the United States and southern Canada. The “Baltimore oriole” form is found throughout the eastern and midwestern sections of this range, and the “Bullock’s oriole” form is found in the far west. Hybrids of these two forms are found extensively throughout the Midwest. Both varieties spend the winter season in shared territories throughout Mexico, Central America, and tropical South America. On a few rare occasions, the “Baltimore oriole” form has been seen in Ireland, England, and on the European mainland.
Northern orioles prefer open woods that ideally have a mix of deciduous and coniferous trees. They can be found, though, in farmlands, parks, and even in suburban neighborhoods. Nests are most commonly built in maples, willows, or apple trees.
Northern orioles eat insects (especially caterpillars (including web worms and gypsy moth larvae), adult moths and butterflies, beetles, ants, grasshoppers, wasps and aphids). They are particularly important predators of tent caterpillars (Malacosoma disstria and M. americanum). Northern orioles also eat mollusks, and a variety of fruits and nectars. They can be attracted to bird feeders by the placement of orange halves, fruit jellies, peanuts, and nectar (as in hummingbird feeders). They have also been known to eat peas from cultivated garden plots and fruit from orchards. They also raid nests of other birds for eggs. Northern orioles forage for insects in trees and shrubs. They characteristically make short, darting flights through the tangles branches in pursuit of their prey.
Northern orioles are in turn preyed upon by a variety of other species. Common grackles, crows, blue jays, screech owls, and black billed magpies are common avian predators. Gray squirrels, fox squirrels, and domestic and feral cats are common mammalian predators. Gopher snakes, because of their ability to climb about in the high, slender branches of trees are also significant nest predators.
Male northern orioles return to their northern breeding ranges in late spring. On their arrival, they vigorously establish breeding territories. These territories may be a few acres in size and may adjoin the territories of other males. Territories are claimed by singing and display (hence the very bright colors of the male plumage). Males attain their distinctive plumage by age 2 and then, commonly, begin to stake out territories and attempt to attract mates. Immaturely plumaged birds, though, have been known to successfully mate. Intruders into the established territories are energetically pursued and chased away. When the females arrive they are also initially chased away by the males until courtship rituals begin. Courtship consists, in part, of the male hopping from perch to perch around the female which triggers her “chatter” vocalizations and wing drop displays. The pair then flies about in the male’s territory while loudly singing. They then return to their perches and repeat these actions until finally mating is accomplished.
The female then builds the uniquely structured, hanging nest. She locates it most typically in the upper regions of a tall, deciduous tree with drooping branches (as mentioned previously, maples, willows, and apple trees are very commonly used for nest sites). The opening to the nest chamber is via a small hole at the top of the nest sack. The slender branches onto which the nest is affixed provide excellent protection from large predators. Selection, though, of branches that are too slender can lead to loss of the nest and its contents during wind and thunderstorms. The female begins the nest construction by hanging strips of coarse plant fibers, string, animal hair, bark, grasses, and even Spanish moss from the selected tree branch. She steadily works these coarse fibers together into coherent sack. The construction of the nest sack takes 5 to 8 days. The inside of the nest is lined with a variety of soft materials including feathers, fine grasses, animal fibers, and even dandelion fluff. Usually new nests are built each year although the repair of old nests has been observed. Old nests can also be scavenged for building materials.
Females lay 4 to 6 pale blue to gray-white eggs with brown spots in a single clutch. They lay one egg a day and then incubate the finished clutch for 12 to 14 days. Only one clutch is attempted each season. Both the male and female vocalize extensively during the nest building, egg laying, and incubation periods. Chicks remain in the nest for another 12 to 14 days. They are actively fed by both parents during this time period. The parents, as they have been doing all spring, actively sing during this nestling period. Even the nestlings, after they reach the age of 7 days, begin to join in on the singing.
When the chicks fledge they follow the parents around the territory, again, in a very noisy, vocal manner. One week after fledging, the female leaves the family territory, molts, and then begins her slow migration toward the tropical, winter territories. The male feeds the fledges for another week or two and then begins his own molt and preparation for migration. He leaves his breeding territory in late summer. In mid to late summer, then, the songs of the orioles finally fade from the northern forests.