No Rest for Nesters
by Val Cunningham
One strand of grass, one old hosta leaf, one pine needle at a time, birds are frenetically creating structures for holding their young.
Birds seldom sit idle at any time of year but they’re at their busiest right now, intent on completing the two major tasks of their lives: finding a mate, and then constructing a nest to hold their brood.
All birds, whether single parents or mated pairs, function as their own design/build teams during nesting season. No bird sees how its parents built their nest, so each follows a basic design stored in their brain, making improvements as they gain experience over the years.
Before we go any further, we should give silent tribute to what birds are able to accomplish, without hands and especially without thumbs. With little more than a beak and feet, they lift and carry, push and pat, weave and knot, until they have a structure strong enough to withstand both the elements and the exuberant activity of their growing brood.
Gathering building materials
Birds use their tools in ingenious ways to get the job done. Some birds tug at small twigs, others drop to the ground to pick up plant debris (even trash, such as gum wrappers, bits of plastic, cigarette filters), or strip thin bark from shrubs and trees. Some roll up balls of mud, and a few even pull fur from sleeping dogs or raccoons.
Then, beaks stuffed with building materials, they travel back to a tree fork, house eave, plant basket, tree hole or other nest site.
Even though nests may look pretty much the same to us, there’s a great deal of variation from species to species, in terms of shape and size, building materials and location. The familiar cup nest is the most widespread type, the kind of nest built by cardinals, goldfinches, hummingbirds, blue jays and many others.
After building a strong base and anchoring it firmly to twigs or branches, birds form the nest walls, often flying around the cup as they twine long grass strands around the outside. The female bird frequently sits in the cup, twisting and turning to make sure it conforms to her body. After all, she’s the one who’s going to spend several weeks in there, sitting on her eggs.
Stealing from spiders
Bird-nesting season can be tough on spiders, since quite a few bird species steal spider silk either to hold nests fast to supports, or weave it into nest walls. Spider webbing stretches and expands as young birds grow and push against nest walls.
Usually the final step is to line the cup with soft material, such as animal hair, moss, feathers and/or plant down, like fluffy thistle or dandelions gone to seed. Some species, from hummingbirds to thrushes, go a step further and add lichen or leaves to the outside of the nest, helping to camouflage it from predators. Soon after all these steps are taken, a process that may take from several days to two weeks or more, a female bird will begin laying eggs.
Orioles are champs
One of the master builders in the bird world is the Baltimore oriole, whose purse-shaped nest hangs from the end of a tree branch. Females do most of the building, first attaching strands to twigs, then weaving and stitching fibers with thousands of complex knots and loops—using only her beak. Oriole nests are so tough and resilient that we often see them still hanging, even up to a year later.
The fact that nests vary in appearance and location from species to species is a survival strategy. If all nests all looked the same, it would be much simpler for cats, squirrels, snakes and raccoons to find an easy meal of eggs or nestlings.
After all the labor and energy that goes into building a nest, these are only temporary structures. A nest after young birds fledge often is not a pretty sight, infested with insect parasites and bird poop, and usually a bit ragged around the edges. Very few birds ever recycle their old nest, instead starting all over the next time breeding season rolls around.
St. Paul, Minnesota resident Val Cunningham, leads bird hikes for the St. Paul Audubon Society and writes about nature for local, regional and national newspapers and magazines.
Some birds nest in tunnels, others in tree holes, while a few even lay their eggs in piles of sand. The bald eagle’s huge platform nest is hard to miss, while very few of us ever spot a hummingbird’s tiny nest attached to a branch. Some nests are mere scrapes on the ground while others are elaborate artificial islands built on a base of stone.
Learn about the huge variety of nest structures in Avian Architecture: How Birds Design, Engineer & Build, by Peter Goodfellow (Princeton University Press, 2011). This fascinating book holds 300 color images and 35 case studies, outlining the many nest types in the bird world.
AN AVIAN ‘HOME STORE’
Make life easier for your backyard birds by setting out items they can use to build their nests. Good choices are 6-inch lengths of string and yarn as well as fur from your cat’s or dog’s comb. (Please do not offer lint from your dryer, since this holds water after a rain and can chill young birds.) Drape string, yarn and/or fur on tree limbs and watch birds hustle in to carry it off.