How Orioles Build Those Incredible Hanging Nests

The delicate-looking structures are stronger than they seem, and come in a variety of shapes and materials.

Suspended like a basketball net from a high-up branch, an oriole nest stands out from any other North American bird鈥檚. With hundreds of thin, intertwined fibers, the seemingly delicate cradle can carry up to seven eggs and last for months beyond its intended purpose鈥攁 testament to the skill and dedication of female orioles.

鈥淚t鈥檚 absolutely fascinating to sit and watch them weave,鈥 says Nancy Flood, a Thompson Rivers University biologist who鈥檚 studied orioles for 40 years. 鈥淵ou 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.鈥

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鈥檚 immediately available around the breeding site. Baltimore Orioles like to snap up the fluff that falls from cottonwood trees, whereas Scott鈥檚 Orioles pull pieces from the Joshua trees in which they nest.

Kenn Kaufman, field editor of 探花精选 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.

鈥淭hey鈥檙e making a conscious choice in what materials they use,鈥 Kaufman says. 鈥淪he wasn鈥檛 just flying down and getting a piece of grass. They鈥檙e fully working and getting these fibers.鈥

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. 鈥淲hat鈥檚 remarkable is that microfilament is lethal for birds; they get tangled in it and die,鈥 Flood says. 鈥淔or an oriole to be able to extract it and actually weave it into a nest is a testament to its skill.鈥 

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  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 ). The birds don鈥檛 typically recycle their creations鈥攊nstead, they might take material from old or failed nests to build the new one. 

Experts aren鈥檛 sure why orioles and other birds have adapted to build hanging nests. The most obvious benefit is that the deep cups and narrow entranceways鈥攖wo to three inches wide鈥攑rovide 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 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 cowbirds and crows.

Ultimately, an oriole鈥檚 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鈥檚 genes, Flood explains. 

But both Flood and Kaufman agree that even if the oriole鈥檚 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.