Suspended like a basketball net from a high-up branch, an oriole nest stands out from any other North American bird’s. With hundreds of thin, intertwined fibers, the seemingly delicate cradle can carry up to seven eggs and last for months beyond its intended purpose—a testament to the skill and dedication of female orioles.
“It’s absolutely fascinating to sit and watch them weave,” says Nancy Flood, a Thompson Rivers University biologist who’s studied orioles for 40 years. “You see the female poking one end of the string through, and then pulling her head back to weave it out, just like when you crochet or knit a bag. They can spend half an hour doing that, then go away to get another long piece of grass and do more.”
A group of more than 20 species, New World orioles are often recognized by their vibrant yellow or orange bodies and jet-black accents. Their breeding seasons extend from April to July, though their nests can usually be seen well into fall. Male orioles might assist in the gathering of materials, but the craft of weaving the pouch-like nests is usually completed by the females.
Most oriole nests can be found hanging in the canopy of a deciduous tree, snug and secure from predators, but some species in the Great Plains build cup-shaped nests in low shrubs to shield them from the wind. Hooded and Scott’s Orioles, meanwhile, will suspend their abodes from palm or yuccas leaves in the Southwest and tropics.
Nest materials vary as well; females will choose whatever’s immediately available around the breeding site. Baltimore Orioles like to snap up the fluff that falls from cottonwood trees, whereas Scott’s Orioles pull pieces from the Joshua trees in which they nest.
Kenn Kaufman, field editor of Audubon magazine, once watched a Baltimore Oriole return to a patch of swamp milkweed for three days straight, each time stripping off long, strong fibers from the plants to weave into its progressing nest.
“They’re making a conscious choice in what materials they use,” Kaufman says. “She wasn’t just flying down and getting a piece of grass. They’re fully working and getting these fibers.”
Sometimes the birds get more experimental with their hardware. Flood has an oriole nest made entirely out of fishing line pinned to her bulletin board in her office in British Columbia. “What’s remarkable is that microfilament is lethal for birds; they get tangled in it and die,” Flood says. “For an oriole to be able to extract it and actually weave it into a nest is a testament to its skill.”
The weaving process requires patience and finesse. First, the bird winds long fibers around a branch to create the support strands for the rest of the structure. Then, the female makes a series of rapid thrust-and-draw movements with its beak to begin forming the pouch. She uses more flexible fibers to create an outer bowl before switching to springier fibers for the inner bowl. Downy fibers complete the nest and provide a soft lining to cushion the eggs. In all, construction can take between one to two weeks.
This complex process results in a durable structure (in one study, 85 percent of nests were still in place after a year). The birds don’t typically recycle their creations—instead, they might take material from old or failed nests to build the new one.
Experts aren’t sure why orioles and other birds have adapted to build hanging nests. The most obvious benefit is that the deep cups and narrow entranceways—two to three inches wide—provide better protection from predators and brood parasites. Oriole species with more concealed nests, including Baltimore, Orchard, Scott’s, and Hooded, tend to have shallower pouches, typically ranging three to four inches in length. In contrast, Altamira Orioles and Bullock’s Orioles have much deeper nests. Flood says she’s seen 18-inch-long Altamira nests hanging from power lines in Mexico. In this case, their depth affords them much-needed protection from Brown-headed Cowbirds and crows.
Ultimately, an oriole’s ability to create these architectural wonders is driven by instinct, not creativity. Through evolution, the birds have become increasingly adept at weaving hanging structures that increases the chances of offspring surviving. If a nest breaks, there will be no chicks to carry on the faulty nest builder’s genes, Flood explains.
But both Flood and Kaufman agree that even if the oriole’s craft is instinctual, it takes time and training to perfect it. In other words, only an expert nest builder would be able to take a snarl of fishing line and turn it into a sanctuary.