Small Songbirds in Backyard Nesting Boxes, SF Bay Area 2024
The video clip above is from the 2022 season archive.
A chestnut-backed chickadee built a nest March 15-19, 2024 and laid eggs March 26-31. Unfortunately she became ill and died in the nesting box before incubation could begin.
In the San Francisco Bay Area, three common cavity-nesting songbird species are small enough to enter a nesting box through a 1-1/8 inch (29 mm) entrance hole:
They are common in Bay Area parks and suburbs, especially where trees and shrubs are plentiful, and they readily occupy backyard wooden birdhouses. You can monitor their nesting behavior without disturbing them by installing a camera inside the box.
The smaller entrance hole excludes house sparrows, an aggressive invasive species that displaces native birds, as well as many predators.
Chestnut-backed chickadees live on the west coast of North America from Alaska to Southern California. They are known for their light and airy chick-a-dee-dee call, broad white stripe under the eye, and deep brown chestnut-colored back. For unknown reasons, the brown color extends over the chest of birds north of Marin County but not south.
Chestnut-back chickadees have been consistently nesting in my backyard bird box for many years. I've maintained a camera in the box since the 2021 nesting season, making it easy to observe and track their activity in detail.
Chickadee nesting activity in my backyard box 2021-2024 (tap for details)
You can often see the Bewick's wren quickly flitting from ground to shrub to branch, probing for insects. It's known for its straight upturned tail with spotted stripes, narrow white over-the-eye stripe, long and narrow curved beak, and melodic warbling songs that are surprisingly loud and clear for such a small bird. I find the songs as enjoyable as those of the canary.
Unlike the chickadee or titmouse, the wren builds its nest mostly with sticks. A pair may build multiple nests but use only one of them in a season. In a previous year, a wren built the nest shown in the photo above but did not lay any eggs in it.
For a 3-D stereo view of this photo, cross your eyes slightly until the two images merge in the middle. You should see 3 side-by-side images, the center one in 3-D. If necessary, tilt your head slightly left or right to fully merge the images.
The plain gray color of the oak titmouse looks like mouse fur. The bird can be found in oak forests but it's also at home in Bay Area suburbs where trees are abundant. The bird has a tufted crown (not visible in the photo) and distinctive jet-black eyes. It has a wide range of gentle calls and songs.
Oak titmouses visit my bird boxes to scout for nesting sites, including the box used each year by chestnut-backed chickadees, but they haven't yet nested here. To see a tabulation of their recent visits, go to Nest Box Visits SF South Bay 2024.
In the following description of chestnut-backed chickadee nesting behavior, click the links to see in-box videos of the referenced behavior. The videos are archived from the 2022 live stream.
Nest Building
The female chickadee builds the nest, starting with a foundation of redwood bark strips torn from a nearby tree and whatever fluffy material she can find nearby, such as flower filaments and cotton pulled from old furniture. The total time to build the nest can range from two days to two weeks.
Egg Laying
Sometime after nest completion, the female starts roosting there nightly, entering the box at dusk and leaving at dawn. When the time is right, she starts laying eggs, one per night in the early morning darkness. She still stays away from the nest during the day, keeping the eggs hidden under fluff.
Incubation
When she accumulates a full clutch of five to seven eggs, she incubates them, starting the day just before the last egg is laid. She settles into the nest cup with back-and-forth motion to nestle her brood patch onto the eggs, pushing aside her nearby feathers. The brood patch is a small bare-skin area that keeps the eggs cozy warm.
She stays on the nest full time, day and night, leaving only briefly during the day to eat and drink. While on the nest, her mate may bring her food. She greets him by fluttering her wings, then takes the food at the entrance hole or inside the box. When she makes her brief trips outside, she leaves the eggs uncovered.
Hatching
After two weeks of incubation, hatching starts. The young develop only during incubation, so they tend to hatch together in one day, even though the eggs are laid over a period of several days. (Simply sitting on the nest it not incubation.)
The young are totally helpless and depend entirely on their parents to survive -- they are "altricial" young, unlike "precocious" hatchlings like chicks and ducklings. Altricial fresh hatchlings are so weird-looking, they inspire space aliens created for movies.
Feeding
Within minutes of hatching, feeding starts and continues practically nonstop during daylight hours until the young are ready to fledge. Both parents make hundreds of trips per day to feed the hungry nestlings.
Initially the young are blind but not deaf. When a parent arrives with food, it chirps to alert the young. They respond by opening their mouths upward for feeding. The young rapidly grow, develop feathers, and change shape. In a few weeks they resemble their parents in size, color, and features.
Favorite foods include caterpillars, spiders, insect eggs, and small bugs of various kinds. They also eat fluffy white/pink sheets that could be flower petals, or insect wings -- I'm not sure.
Waste Removal
Immediately after being fed, the nestling turns around, exposes its rear end to the parent, and excretes a fecal sac (a blob of poop enclosed in a thin membrane). The parent takes the fecal sac away and disposes it someplace far from the nest. This keeps the nest spotlessly clean and removes visual evidence and odors that might otherwise attract predators.
Waste removal continues this way until a day or two before fledging.
Fledging
The young birds leave the nest already knowing how to fly, having practiced inside the box. They leap from the box entrance hole and fly away. They all fledge within 24 hours from first to last. I've tried to track them to see how they interact with their parents and each other, but they always leave the yard immediately and I don't see them again.
You can read about previous season activity in detail:
