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How do birds know how to build such intricate nests?

St Paul StarTribune by VAL CUNNINGHAM , CONTRIBUTING WRITER
May 12, 2020

DON SEVERSON – Female ruby-throated hummingbirds are the nest builders.

I’d bet that when most of us think of birds’ nests, we conjure up an image of a robin’s cup, with its hardened-mud base and rather haphazard-looking grass and weed-stalk sides.

But birds build a wide variety of nests out of a wide range of available materials, everything from the streamside burrow of the belted kingfisher to the intricately woven pouch fashioned by Baltimore orioles. Blue jays use twigs, bark and moss to create their large nests with a rounded center. Black-capped chickadee nests work from a template of a moss bowl lined with animal fur, built inside a nest box or tree hole. Gray catbirds often wind grapevines around their nest’s exterior, a natural choice since they so often nest inside grapevine tangles.

Each species has its own nest style, and here’s an amazing thing: No bird has ever observed its parents building their nest, yet in her very first season a female bird (it’s usually the female) builds exactly the nest characteristic to her species. How can that be?

The basic instructions — the size, shape and generally, the materials — are instinctual, hard-wired into their brains, a good strategy for survival of the species. But birds learn to improve their nest-building as they gain experience: In their second and third years, nests may be more tightly woven, or filled with softer materials for their chicks’ comfort or placed in a spot that offers more shelter from the elements.

A Cedar Waxwing plucks cattail fluff for its nest. Photo by Jim Williams

As a rule, females are the builders. Ruby-throated hummingbird females fashion their tiny nests from plant fiber, moss and spider webs, incubate their two eggs and raise the young alone — and then turn around and do it all over again in a single summer. A female oriole spends up to a week bringing in grasses and plant stalks to weave into an intricate purse shape at the tip of a branch, to foil predators. However, in the blue jay world, both genders help create the nest from twigs, bark and mosses.

Some birds handle it like marsh wrens do, where the male builds many starter nests around his territory, then the female chooses one and puts her own stamp on it by adding lining materials.

It’s marvelous, in the truest sense of the word, that birds create such intricate structures using their beaks as their only tool. It’s almost incomprehensible to such a hand-oriented species as we are, but nest building is a hands-off affair. I’ve seen naturalists leading classes about nest-building for kids at nature centers, noting their astonishment (and frustration) as they try to move fibers and string around with their noses.

Another remarkable thing is that birds put so much effort into building a nursery for their offspring, and then never use it again. Once the young fledge, the nest is abandoned (although some robins re-use the mud base for their second nest). Noted author Kenn Kaufman calls birds’ nests “tiny marvels of disposable architecture.”

Birds go to great lengths to hide their movements while they’re engaged in building their nests, knowing that predators (like cats, hawks and squirrels) are on the lookout for just such activity. And they hide their structures deep in a shrub, vine tangle or high in a tree, because many other species of birds and mammals seek bird eggs and young as a source of easy protein.

Nest-building season is a feverish time for birds. They need to get their nursery set so they can get down to the serious business of raising the next generation.

St. Paul resident Val Cunningham, who volunteers with the St. Paul Audubon Society and writes about nature for local, regional and national newspapers and magazines, can be reached at valwrites@comcast.net.

Building supplies

Make life easier for your backyard birds by setting out items they can use to build their nests. Good choices are fur from your cat or dog’s comb. Please do not offer lint from your dryer, since it ‘melts’ when it gets wet and makes the nest unstable. Bits of wool, twigs and small sticks, pieces of dry straw, native plant fluff, dry cattail fluff. You can drape it on tree limbs or put it in a clean suet feeder and watch birds hustle in to carry it off.