“To hear an oriole sing
May be a common thing —
Or only a divine.”

Emily Dickinson from “The Oriole’s Secret”

Last month, I heard an unfamiliar sound in our backyard. I strained my ears to try to identify the vocalist performing so melodiously from the upper branches of the old apple tree behind our barn.

By late April and early May most of the summer songbirds have returned to their nesting grounds in Southern New England. Each year, I happily welcome the winged migrants to our land, with transient birds signaling the ever-turning of the season. This season of flora in full glory brings the insects, worms and assorted bugs needed for feeding voracious hatchlings.

The lone songster behind the barn was late to the scene. Already, we had tree swallows circling the back field, wood and hermit thrush were singing from the nearby woods, common yellowthroat warblers darted through the brush along the field edges, and the house wren had taken up residence in the small wood abode provided by the kind human host.

As I walked toward the sound, I had an inkling of who the performer might be. But, not being familiar with its tune, needed to make visual contact to be sure. I stopped about 20 yards from the tree and sure enough a sudden flash of bright orange and gold confirmed my suspicion — a male Baltimore oriole.

I use several references and guidebooks for learning more about the avian population of our region. One of my favorites is a website maintained by the Cornell Lab for Ornithology – All About Birds. It also provides a sample of each bird song which is helpful for identifying a bird by sound. Here is what I found about the Baltimore oriole, Icterus galbula, from All About Birds:

Size and shape: Smaller and more slender than an American robin, Baltimore orioles are medium-sized, sturdy-bodied songbirds with thick necks and long legs. Look for their long, thick-based, pointed bills, a hallmark of the blackbird family they belong to.

Color pattern: Adult males are flame-orange and black, with a solid black head and one white bar on their black wings. Females and immature males are yellow-orange on the breast, grayish on the head and back, with two bold white wing bars.

Behavior: Baltimore orioles are more often heard than seen as they feed high in trees, searching leaves and small branches for insects, flowers and fruit. You may also spot them lower down, plucking fruit from vines and bushes or sipping from hummingbird feeders.

On their breeding grounds in Eastern and East-Central North America, you’ll most often find orioles high in leafy deciduous trees, but not in deep forests; they prefer open woodland, forest edges, river banks and small groves of trees.

Migration: Baltimore orioles spend summer and winter in entirely different ranges. From early April to late May, flocks arrive in Eastern and Central North America to breed from Louisiana through central Canada. They start to leave as early as July for wintering grounds in Florida, the Caribbean, Central America and the northern tip of South America.

Food: Baltimore orioles eat insects, fruit and nectar. The proportion of each food varies by season. In summer, while breeding and feeding their young, much of the diet consists of insects, which are rich in the proteins needed for growth. In spring and fall, nectar and ripe fruits compose more of the diet; these sugary foods are readily converted into fat, which supplies energy for migration.

Nest: The female chooses a nest site within the territory defended by her mate. She anchors the nest firmly to a fork in the slender upper branches of a tree. Baltimore orioles often nest in American elms, but will build in other trees, especially maples and cottonwoods. The distinctive nest usually hangs below a branch but is sometimes anchored along a vertical tree trunk. Baltimore orioles build remarkable, sock-like hanging nests, woven together from slender fibers. The female weaves the nest, usually 3-4 inches deep, with a small opening, 2-3 inches wide, on top and a bulging bottom chamber, 3-4 inches across, where her eggs will rest.

She anchors her nest high in a tree, first hanging long fibers over a small branch, then poking and darting her bill in and out to tangle the hank. While no knots are deliberately tied, soon the random poking has made knots and tangles, and the female brings more fibers to extend, close and finally line the nest. Construction materials can include grass, strips of grapevine bark, wool and horsehair, as well as artificial fibers such as cellophane, twine, or fishing line. Males occasionally bring nesting materials, but don’t help with the weaving. The nest is built in three stages: first, the female weaves an outer bowl of flexible fibers to provide support. Next, springy fibers are woven into an inner bowl, which maintains the bag-like shape of the nest. Finally, she adds a soft lining of downy fibers and feathers to cushion the eggs and young.

Nesting: The clutch size is three to seven eggs with one brood per breeding season. The eggs are up to an inch in length and less than an inch in width. The incubation period is 11-14 days and the nesting period is also 11-14 days. The eggs are pale, grayish or bluish white blotched with brown, black, or lavender.

Conservation: Baltimore oriole populations have been declining throughout their range with Canada experiencing over a 3 percent loss per year (resulting in a cumulative loss of 24 percent) between 1966 and 2010, according to the North American Breeding Bird Survey. “Partners in Flight” estimates the global breeding population at 12 million. Because they breed in North America and winter in Central and South America, Baltimore orioles are vulnerable to deforestation and habitat loss in many nations.

Backyard tips: Baltimore orioles seek out ripe fruit. Cut oranges in half and suspend them from trees to invite orioles into your yard. Planting bright fruits and nectar-bearing flowers, such as raspberries, crab apples, and trumpet vines, can attract Baltimore orioles year after year.

Summer is here, the Baltimore orioles have returned and lucky are those fortunate enough to hear their song, see their amazing pendulous nests and witness one of the most colorful birds in our region.

Bill Reid is the chief ranger of The Last Green Valley National Heritage Corridor and has lived in the region for more than 35 years. He can be reached at bill@tlgv.org.