Nesting Strategies

by Mike Stiles

April is the month when many of our local birds start proclaiming territories, choosing mates, and building nests. Avian battles for territory are raging, and the weapon of choice is song. While researching an upcoming field trip dedicated to this topic, I came upon some interesting tidbits for some of our more common nesting birds I would like to pass on.

Wrentit — This common but seldom seen bird has many unusual traits. Both males and females sing for territory, and they do it all year long. Wrentits bond for life, and will breed no more than 400 meters from their place of birth. They are called the most sedentary birds in North America. Both sexes take part in nest building, incubation, and feeding of young. The nest is started by building a bowl shape with spider web, strengthened with bits of bark that are carefully peeled from nearby trees and shrubs, and then lined with softer material. The spider web has been observed being collected by the bird’s tail then transferred to the bill. Interestingly, Wrentit taxonomy has been questioned since its discovery, and is thought to be more closely related to Asian babblers than any North American bird. It is the only representative in its family.

Bushtit — These vocal and gregarious birds are common in our area, and are almost always seen in small flocks. They seem to be constantly making some kind of chip call or predator warning, but they have no real song. Bushtits build a long hanging nest, also started with spider web, then covered with plant material and lined with softer plant material or hair, and camouflaged with leaves from the tree the nest is in. The birds will often sit in the nest, stretching the material downward while material is added, to end up with a soft, foot long, sock-shaped nest, with the entrance hole on the side near the anchor point. Other adults or juvenile birds often act as “helpers” of the breeding pair in the nest building, incubating, and rearing of the young. The pair and the helpers and young will all sleep in the nest together, a very rare occurrence in the bird world.

Brewick's Wren

Bewick’s Wren — This cocky denizen of the chaparral can be quite vocal, singing from the top of exposed perches, head thrown back, loudly proclaiming his territory, sometimes dueling with the neighboring Bewick’s Wren just 20 feet away. Those two males learned their song not from their fathers, but from neighboring male wrens, and a single male can sing up to 22 different songs. That prompts the old adage “if you hear a song in the chaparral you don’t recognize, it’s a Bewick’s Wren.” They build their cup shaped nest in rock ledges, old woodpecker holes, and other tight spaces, and often line the nest with shed snakeskin. This wren has suffered for nesting space where its range overlaps with the even more aggressive House Wren.

Spotted Towhee — In a daily time budget study, male Spotted Towhees spent the majority of their daylight hours in the breeding season singing and eating. I will refrain here from making a joke about human males. They have time to spare since the male does not partake in nest building or incubating eggs, though they will visit the nest with food once the eggs have hatched. Their cup-shaped nest is, about 90% of the time, built in a depression in the ground with the upper lip of the nest at ground level. It is not clear if the bird excavates the nest hole or uses an existing depression.

Chestnut-backed Chickadee — This tiny west coast bird nests exclusively in cavities and will readily use nest boxes. The female will watch while the male explores several likely locations then will pick the one she wants. The male’s work is done while the female builds the nest. She will line the bottom of the area with moss and bark, and about half the remaining nest material is hair from rabbit, coyote, and deer, along with other animal hair and even string and yarn. She will also weave a thick “blanket” of hair to cover the eggs when she leaves. Only the female incubates the eggs, while the male delivers food to her. After the eggs hatch, up to 200 food deliveries a day have been observed to the apparently voracious young.

Annas' Nest

Anna’s Hummingbird — There are nesting records for this bird in every month of the year in our mild coastal climate. For lack of a song, the male Anna’s Hummingbird performs aerial displays, climbing straight up in the sky above the female, and diving straight down with a sharp upward turn just above the female, while making a high pitched note, all the while keeping his brilliant throat patch toward the sun for full effect. Not very long ago, it was discovered that the chip note at the bottom of the dive is not a vocalization, but a result of wind through the tail feathers. For her nest, the female will gather downy plant material and form it into a cup about the size of a half walnut shell, bound with spider web. She will decorate the outside with bits of lichen and bark, and even paint chips, and she will often steal material from other, even active, nests. When the young are being fed, the female will switch from her main diet of plant nectar, and catch insects for her brood.

Breeding birds this time of year are easy to hear, but it takes great patience and some luck to find these hidden and camouflaged nests. Please don’t disturb them, and take care when pruning shrubs and trees the next few months.