Adult male Baltimore oriole.

April 15, 2009: The madre de cacao tree at the entrance to Tikal National Park in Guatemala has no leaves but is in full pink bloom. It is easy to see the small flock of exquisite male Baltimore orioles with their brilliant plumage of flame-
orangebellies, blackheads and tails, and black wings with bright white and orange patches. Along with the females, who are dull olive-yellow, they are sipping nectar from the delicate blossoms, garnering the nourishment they will need to fly north to breed.

May 7, 2009: The clear, flute-like bugling call of the Baltimore oriole rings from the treetops at Skokie Lagoons. The orioles are back! Amazingly for such a bright, colorful bird, they can be difficult to spot as they hide behind leaves. When they fly out to another tree and perch in the open, they are a sight to behold.

Oriole names can be confusing. The “old world” Oriolidae family ranges from Europe to Australia. Our “new world” orioles, including the Baltimore oriole Icterus galbula, belong to the family Icteridae, along with blackbirds, grackles, cowbirds, meadowlarks and the bobolink. Old and new world orioles are not related. Because of their similar coloring, size (average 7 inches long), behavior and diet, however, it was inevitable that human immigrants from the old world would name these new world look-alikes “orioles.”

My childhood bird book, “From Robin to Junco by Mary Curtis, explains that Lord Baltimore was so delighted with the colors of the oriole that he adopted them for his coat of arms. Catesby’s 18th-century “History of North Carolina,” however, claims that because the oriole resembled Lord Baltimore’s coat of arms, it became the Baltimore oriole. It is a chicken-and-egg story.

According to studies by Rising and Flood in 1998 and Hammerson in 1996, “Baltimore orioles breed from central Alberta, southeast through the Great Lakes, extending east to Nova Scotia, and south to the interiors of the Gulf Coast states, and west to the western edge of the Great Plains. Baltimore orioles winter in coastal California and Yucatan south through Central and South America; also in Florida and Cuba.”  Habitat change, new research and particularly climate change will keep breeding range maps in constant flux.

The males arrive on our northern breeding grounds two or three days before the females. They are apt to return to a previous nesting area. Courting begins as soon as the females arrive. Males can be observed chasing other males and females from tree to tree across open areas. While courting the female, the male will perch on a branch near her and display with an exaggerated bowing motion, showing off the brilliant orange on his back and belly. Previously, the birds were considered monogamous, but research has shown that they might have brief affairs with others.

For their nests, orioles will typically choose a tall, deciduous tree such as elm, cottonwood, box elder or maple, usually on a woodland edge, often near water, often in a residential neighborhood. The nest is built by the female near the edge of a drooping branch at least 30 feet high, behind thick leaves. She attaches several long strands to the branch. Then she collects individual new threads and assembles a complex, unusual pouch-like shape. Materials include any available fibers, even strands of yarn and horse hair from manes and tails. It may take the female five to eight days to weave this cradle, which swings from the branch in the wind. Curtis says of the construction scene, “While she is building their picturesque home, he does nothing much but fly around and sit and watch her and look gorgeous.”

Baltimore orioles have only one brood a summer, while many other species nest two or three times. An average clutch contains four eggs colored a pale grey or bluish white, with black or brown splotches or streaks. The incubation period is approximately 12 days. The hatchlings stay in the nest for about another two weeks and are fed by both male and female. When ready to migrate south again in late July or early August, earlier than many songbirds, females and juveniles can be seen flocking together, whereas the male often remains solitary. The male is 2 years old before he attains the beautiful colors we see.

Baltimore orioles primarily eat insects. They are considered particularly useful to humans due to their preference for caterpillars, when the insects are most harmful to plants. They have a particular fondness for tent caterpillars.

They are also attracted to nectar and fruit. Mary Singh, who lives about a block from the lake in Evanston, has built an elaborate oriole attractor in her back yard. Several orioles stop to feed together as they are migrating through. They will consume about half of the sections of one or two oranges and ignore others completely, for no apparent reason. Grape jelly is said to be another favorite attractant.

An especially good feature of Baltimore orioles is that one does not have to be an early birder to see them. They are active all day. For the last two years, they have nested in the cottonwoods at Northwestern’s sailing beach, and they were seen chasing each other there this spring. Unfortunately, they show no signs of having stayed to nest.

If anyone has found a Baltimore oriole nest in Evanston, please e-mail that information to libbyhill@comcast.net.