Bird Nests

by Mike Stiles

In this part of the world, May is the month for nest-building of many of our breeding birds. This month I will discuss the fascinating art of avian nest construction.

From a simple scrape in the sand to elaborate stick castles, or maybe the oddest one yet—the swiflets in Southeast Asia who make their nest from their own saliva (and then made into bird’s nest soup), the diversity of nest construction is incredible.

In San Luis Obispo County the Bushtits are building foot-long hanging sock-like baskets with a small opening at the top and room at the bottom for communal egg laying by several females. Warbling vireos are building small hanging woven cups in trees near a creek, and Hooded Orioles are building large hanging nests in palm trees, woven from fiber pulled from the edges of the palm leaves. Ornithologists who have de-constructed some of these nests have found the fibers elaborately woven and tied into overhand knots and half-hitches, and even some in slip knots. Not an easy feat with no opposable thumbs.

Many birds nest in cavities drilled out by woodpeckers and coveted by other species. Western Bluebirds and Tree Swallows use these holes and, unfortunately, so do the introduced European Starling and House Sparrow who can out-compete our native species for the holes. House Wrens use any kind of hollowed-out area available in the bark of trees or in old scars, often in Sycamores trees.

Nest building materials vary widely and encompass plant and animal materials, rocks, mud, and even tin foil, ribbons, and snake skins. The nests are often lined in softer material such as hair and feathers, and they can be decorated with lichen for camouflage, and even held together with spider web. Where nesting material is scarce, large seabird and penguin colonies often find it easier to steal material from their neighbors than to find their own.

Size and complexity range from a few sticks in the fork of a branch for the Mourning Dove, or the hummingbird nest about as big as a walnut shell, to the large aeries of eagles. Eagles add new nest material every year, and one 30 year old Bald Eagle nest weighed 2 tons when it finally fell from the tree in a storm.

Once the eggs are laid, incubation times range from as little as 10 days for some woodpeckers and small songbirds to as long as three months for albatrosses. Many birds will delay incubation until all the eggs are laid to assure that the young hatch at about the same time. Owls are one exception and will incubate each egg as it is laid. It is common to see a group of young owls of varying size. If food is not readily available, this strategy will allow at least the larger, stronger young to survive.

As you can imagine, nest sanitation is critical with a brood of hungry chicks in the nest for several weeks. Some birds are not very careful and their nests are covered in their "white wash," while other birds are fastidious and constantly keep the nest clean to avoid disease and detection by predators. Cavity nesters instinctively eject through the nest opening, and some young eliminate in a membranous fecal sac, which is carried away (or eaten) by the adults.

It is always a treat to find a nest, as they are well hidden for obvious survival reasons. So please, when you are pruning your trees and shrubs at this time of year, be aware of scolding birds, for it may indicate that a nest is nearby.

One last thing I want to mention, and I get asked about this every year at nesting time, and that is what to do if a nestling bird has fallen from the nest. If the young bird is feathered and hopping around, the adults will feed it on the ground. It is best to leave it alone. If the bird is very young and still without feathers, it is acceptable to try to place the bird back in the nest.

Photos courtesy Wikipedia and Sibley Nature Center
Burrowing Owl on banner by Cleve Nash.