Baltimore orioles are slightly smaller and more slender than American robins. Look for a thin, sharp, silver, gray, or black bill with a wide base. Underparts range from dull yellow to flame orange. Adult male Baltimore orioles have an entirely black head and upper mantle, an orange middle and lower back and rump, and orange shoulder patches. Wings are black with one white wing bar, and tail has a central black V, bordered on all sides by orange or yellow. Adult female Baltimore orioles vary from drab to bright yellow to bright orange. Back and wings are dull gray, olive, or brown, with two white bars. The tail is uniformly dull orange to brown. The head and nape can be gray, olive or brown, turning darker with each molt. The oldest known wild Baltimore oriole was more than 11 years old. The species molts once a year, after breeding and before and during southbound migration.
The song of the Baltimore oriole is melodious and flutelike in tone, but usually a short series of notes, often repeated a few times, and often interrupted by pauses. The song can be mimicked by whistling, but isn’t amenable to transliteration—that is, there’s no who cooks for you, who cooks for you alllll, or Old Sam Peabody Peabody Peabody for Baltimore orioles. Males often sing from high, open perches in their territories. Female Baltimore orioles sing, too, often while foraging, but a simpler song. Sometimes, pairs are said to sing duets! Both males and females give an alarm call that can be transliterated as chuck, often repeated when humans or predators are nearby.
A few Baltimore orioles winter in Florida, but most arrive at the Gulf Coast in April, and head north in April and early May. They breed east of the Rocky Mountains, from northeastern British Columbia across southern Canada to the Great Lakes, north into New Brunswick, and south nearly to the Gulf of Mexico. They frequent treetops in open deciduous forests and riparian areas, as well as human-altered environments, such as city parks, wooded suburbs, and orchards.
Baltimore orioles can be lured to backyard feeding stations with orange slices and grape jelly. In nature, they prefer dark fruit, such as mulberries and black cherries, to pale-when-ripe fruit. Especially during breeding season, they devour caterpillars—even hairy ones that many other bird species avoid—insects, and spiders. They forage by gleaning from leaves and branches, and pick insects from spider webs. They are an important predator of tent caterpillars. They also sip nectar from flowers and hummingbird feeders. Commercial oriole feeders have bigger, sturdier perches and ports than hummingbirds, and willingly accept less sweet solution than hummingbirds. A ratio of five or six parts water to one part sugar is fine for orioles. They are also attracted to bowls of dark-colored jelly, mealworms, and slices of orange and apple. Because insects are an important part of their diet, avoid pesticides. Poisons that target larva, grubs, and components of the oriole’s diet not only removes a food source, but may harm the birds, especially nestlings, as well. Plant berry-bearing shrubs and trees to provide a natural food source for orioles in your yard. Favorites include mulberries, raspberries, blackberries, serviceberries, elderberries, blueberries and huckleberries. Nectar-rich flowers that attract hummingbirds, such as petunias, trumpet creeper, native honeysuckle, and bleeding hearts, also attract orioles.
Baltimore orioles are considered to be socially monogamous—both parents care for the young—but extra-pair copulation is fairly common. Males return to nesting areas first; females follow a few days later. Females pick the nest site, and construction usually takes about a week. The gourd-shaped, pendulous nest is built in three phases: an outer bowl-shaped support structure is built first of plant material, animal fur (especially horsehair), or human-made fibers such as string; then, flexible fibers, such as from grapevine or Spanish moss, are woven into an inner bowl; and finally, downy fibers, including milkweed seed plumes and feathers, are used to line nest. Nest lining continues even as eggs are being laid. Baltimore orioles rarely reuse nests, but regularly dismantle and reuse materials from previous years’ nests. Clutch size is usually four or five, but can be as large as seven. Incubation, by the female only, lasts 11 days to two weeks. Sometimes the male brings food to his mate, but often the female leaves the eggs to forage. Hatching is usually synchronous, but can occur over two or three days. Both parents feed the young—for the first few days by regurgitation, and then by bringing caterpillars, insects and spiders. Before fledging, the young sometimes cling to the outside of the nest or nearby branches. Fledging occurs 11 days to two weeks after hatching, by which time the young are fully feathered, but have a stubby tail and wings. Fledglings are able to fly only short distances for the first few days. Parents feed the young for up to two weeks. Females leave their brood first, leaving the males to feed the young for a few more days. If nesting successfully results in fledged young, Baltimore orioles do not attempt a second brood. If the first nest fails early, however, they may try again.