More than 700 bird species breed in North America, and the variations in the way they build nests, lay eggs and raise their young are fascinating and complex. In my little corner of the world (Central Arizona) this year, I've had the opportunity to observe and photograph the nesting cycle of a number of year-round residents, as well as birds that winter here or have stopped by briefly to breed and raise their young before continuing on their migratory journey.
Long before nestlings arrive, birds will have selected a breeding territory, a place that provides reliable food sources and protection from predators. Non-migratory species, such as our Cactus Wren or Gila Woodpecker, may either maintain a territory throughout the winter or establish a new one in the spring. Migratory birds begin looking for and defending a territory as soon as they arrive in the spring.
Once territories have been claimed and mates have been chosen, the task of building a nest begins in earnest. Most birds construct nests from natural materials, such as leaves, mud, grass and fur, others may add human-made items such as plastic, paper and bits of yarn or string. Females typically build nests, but sometimes both parents or just the male will build it.
Whatever form it takes, the nest is built to provide a safe place for eggs and young birds to develop, and the variety of nests are extremely diverse, although each species has a characteristic style.
THE CACTUS WREN
Our resident Cactus Wrens build large football-shaped nests with tunnel-like entrances. The female initiates nest building, but after she selects the spot, the male pitches in to help. Maybe that's because they typically build two nests – one for their young and one for roosting. The nests will be 3–10 feet above the ground in a cholla, palo verde, acacia mesquite or other desert vegetation where the nest is surrounded by a natural security system of spiky thorns.
The Verdin also builds two nests – one for breeding and a smaller one nearby for roosting. The outer stick shell is an intricately woven ball of thorny twigs, feathers and plant matter built mostly by the male. Inside the sphere is a small cavity lined with spiderwebs, grasses, feathers and plant fibers by the female. The nest entrance is an opening about one inch in diameter, usually on the bottom or side of the sphere.
THE ANNA'S HUMMINGBIRD
The tiny female Anna's Hummingbird builds her thimble-sized nest without the help of her mate. She uses spider webs to make a tiny cupped nest to which she adds bits of bark, leaves or lichen to hide it from predators. The elasticity of the silky spiderweb allows the nest to stretch as the chicks grow, keeping them snug and secure. This nest was so well camouflaged I would have missed it if I hadn't seen her fly into it.
THE AMERICAN ROBIN
There are usually a handful of American Robins that overwinter here each year, attracted to Verrado's tall shade trees above lawns. The female builds her nest from the inside out, pressing dead grass and twigs into a cup shape using the wrist of one wing. The nest I found this year shows some of the creative materials she’s used in her nest, including paper, feathers, bits of yarn and string, and even strips of plastic mylar in addition to grass and twigs. Once the cup is formed, she reinforces the nest using soft mud to make a heavy, sturdy nest and lines the nest with fine dry grass. She will raise two to three broods before returning north.
THE COOPER'S HAWK
This year, I had the pleasure of watching a young Cooper's Hawk pair build their first nest high in a tree near me. Cooper’s hawks are monogamous, and many pairs mate for life, breeding once per year and raising one brood per breeding season. It is the male of this species that builds the messy piles of sticks with a cup-shaped depression in the middle, lined with bark flakes and twigs with just the slightest help from his mate. She does most of the incubating and the male provides food for her. After the eggs hatch, both parents care for the young, who leave the nest after 27 to 34 days when they learn to fly. The parents continue to provide food to the chicks until they learn to feed themselves at about eight weeks old. I never saw any chicks in the nest and one day the pair was gone. I hope they were successful, although I know that is not always the case.
Other birds choose a less labour-intensive way to make a nest, using a hole that already exists. These Mourning Doves, for instance, chose a hollowed out hole in a Saguaro to bring up their young.
Western Screech-Owls also use a natural tree hole or an abandoned woodpecker nest in which to build their nests to lay three or four eggs and will incubate them for about 26 days.
American Kestrels nest in cavities, although they lack the ability to excavate them on their own. They rely on old woodpecker holes, natural tree hollows, crevices and nooks in buildings and other human-built structures. The male (shown here) searches for possible nest cavities. When he’s found suitable candidates, he shows them to the female, who makes the final choice. This nest was in a crevice high in a palm tree above Founder's Park.
BIRDS THAT DON'T BUILD NESTS
Some birds, such as the Bronzed Cowbird, are known as brood parasites and don't build nests at all, but instead lay their eggs in the nests of other birds. Although many birds can recognize eggs they didn't lay and will reject them, in other nests, the intruder birds will grow up with foster siblings of a completely different species, competing with them for more food and can be harmful to its adopted siblings.
Other birds, like House Sparrows and European Starlings, take advantage of holes in roofs to make their nests, stuffing their hole with grass, which looks rather untidy, but does the trick. This Starling is using a hole in the side of a building in downtown Verrado, likely created by a woodpecker originally.
These are just a few of the birds and their nests that I observed on my walks around Verrado this spring. It's easy to see that there are as many varieties of nests as there are species of birds and while species build share characteristic styles, each nest is unique. It's like driving through a neighborhood of track homes where each house looks nearly the same, but the inside reflects the personality of the inhabitants. In my next blog, I'll be sharing some of the babies that were produced during this nesting cycle in Verrado. I hope you'll join me!