Bay Nature magazineSpring 2020

Ask the Naturalist

How Do Birds Know How to Build Nests?

March 24, 2020
robin cup nest
An American robin’s nest built amid the branches of an aspen growing in the Eastern Sierra exemplifies the common “cup”-shaped nest, a type of nest woven by many songbirds using mud, grasses, twigs, feathers, and more. Robins sometimes return to a nest for a second season. (Photo by Brad Rippe Photography)

There are 10,000-plus species of birds in the world, about 1,100 species in the United States, and 350 or so in the greater Bay Area, so there is great variability in nests. But the basic purpose of any nest is to facilitate the raising of young, providing a functional and safe environment for both eggs and babies. (In some species, males also use nest building to attract females. Marsh wrens are a local example.)

There are many ways to accomplish this. Out on the Farallon Islands the common murre simply lays eggs on rocks; our state bird, the California quail, scrapes a depression in the midst of concealing vegetation. Hooded orioles weave pendant nests that hang from the leaves of palm, sycamore, and other trees.

Now, if someone says that you eat like a bird, I’m not so sure that’s a compliment. Many birds dine constantly and poop almost as often. If they call you a birdbrain, though, I might take that as a compliment—although, of course, it depends on which bird they’re referencing. The psittacines (parrots, macaws, cockatoos) and the corvids (crows, ravens, jays, magpies) could be charter members of Mensa. They are super smart and well known for their intellectual accomplishments. Boobies, on the other hand…well, their mothers love them. 

There’s been surprisingly little research done on nest building considering how essential it is to avian survival and to understanding bird smarts. For years, we saw it as a simply innate activity that was totally instinctual. A bird was born already knowing how to build a nest, end of story.But there have been some interesting recent studies of how birds learn and improve in their nest-making ability—and perhaps their reproductive success. 

Several of these nest-building studies have examined captive zebra finches. They make great winged lab rats: they breed and build nests well in captivity, have short generation times, and immediately rebuild nests when their babies have fledged. They’re also passerines, or perching birds, which is the largest and most diverse order of birds —evolutionary success that may be partly due to effective nest building. 

One study found that zebra finches will sometimes change their nesting material preferences in response to their success raising chicks in a given nest. In another study, they adjusted their building techniques to maximize available material, figuring out how to hold long pieces of nest material to fit them through the small entrance of their nesting area. And in the field, other birds have been observed to adapt and change methods between one nest and the next.

These studies indicate that birds can learn from their own nest-building experience, while other studies suggest birds may learn by example from their parents or other familiar birds. When building their first nests, some Baltimore orioles apparently observe more experienced, familiar orioles in their neighborhood and utilize the same nesting materials. This kind of dynamic is known as social learning, similar to what many mammals do.

There’s still an awful lot to learn here. Birds, for example, do not know what they are when they hatch; they learn about their bird-ness through imprinting, or identifying with their parents during an important stage of their development. Could imprinting also play a role in learning to build a nest? How important is social learning in comparison? Do birds with A-plus nest-building skills also do better in other tasks? The research questions are endless. 

As I write this I am in East Africa and, right outside my tent is a tree full of lesser masked weavers. The brightly colored males have created exquisite woven grass nests hanging from the thin, flexible branches of an acacia. They are dangling from their nests vocalizing and displaying for the females flying in. Pick me! Pick me! And at my house in downtown Santa Rosa a bushtit has woven yet another pendulant nest around the branch of a gnarled oak. Practice may not make perfect, but it sure can make a better nest. 

Birdbrain indeed.

About the Author

Send your questions to atn@baynature.org.Santa Rosa-based naturalist Michael Ellis leads nature trips throughout the world with Footloose Forays (footlooseforays.com).

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