South Bay Bird Nesting Box, Chestnut-Backed Chickadee 2021

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The bird nesting box is in a tree in my suburban back yard on the San Francisco peninsula. Since January, the box has been visited by oak titmice, chestnut-backed chickadees, and Berwick's wrens.

The chickadees built a nest and hatched a clutch of 6 eggs. Unfortunately, for unknown reasons, care-taking by the parents suffered a crisis and the nestlings died on April 29. A pair of chickadees (probably the same pair) initiated a new late-season nesting attempt on May 3. Four eggs were laid May 10-13 and hatched May 25-27. The four birds grew successfully and fledged June 16-17.

video: eggs to fledglings

 YouTube channel

Timeline (2021 late-season nest):

Nest building May 3-6 Daytime spent bringing in nesting material; nights spent elsewhere
Egg laying May 10-13 Daytime spent away, nights on nest; 1 egg laid per day before sunrise
Incubation May 12-26 Most of day and all of night spent on nest
Hatching May 25-27 Most of day and all of night spent on nest; frequent feeding
Growing May 26 - June 13 Frequent feeding and waste removal; rapid growth
Fledging June 16-17 Young birds leave the nest

June 16-17: Fledging

The four birds grew up and fledged (left the nest) on June 16 and 17. They will spend a couple of weeks with their parents and then go off on their own. The parents look really worn out, but they will molt and grow a new set of feathers in the fall.

May 26 - June 17: Feeding & Growing

During the day, the mom & dad chickadees frequently bring food and remove waste, about one trip every 5 minutes on average. The nestlings grow rapidly. Peeping became audible starting June 3. They opened their eyes for the first time on June 4. They grew enough feathers to be left alone at night starting June 4.

May 25-27: Hatching

The first and second eggs hatched on May 25, the third on May 26, and the fourth on May 27.

May 12-27: Incubation

To start incubation, the chickadee mom uncovered the three eggs, built a fluffy "cup" to contain them, and began spending most of her time on the nest, leaving occasionally to eat and drink. She no longer hides the eggs under fluff when she leaves. She laid the last (fourth) egg on May 13.

The male occasionally brings her food, like a white worm or green caterpillar, usually at the nest box entrance, but sometimes outside or inside the nesting box.

May 10-13: Egg laying

Eggs were laid in the mornings of May 10-13. The chickadee mom stayed away most of the day (until May 12 when incubation began) and spent nights on the nest. While away during the day, she kept the eggs hidden under a layer of fluff.

May 3-6: Chickadee builds new nest

The chickadees came back with a new, late-season nesting attempt after the loss of their brood at the end of April. I can't be sure, but I think this is the same pair, based on the timing of the nesting attempt in the season. The second day of nest building, May 4, was the busiest with more than 300 trips to bring in material. By the next day, the nest was substantially complete.

The chickadees chose to return to a nesting box on the fence instead of the one in the tree. Cats and squirrels use this fence as a highway. An extra-long roof helps prevent predators from reaching into the nesting box from above.

Timeline (2021 early-season nesting attempt):

Inspection visits Feb, Mar Brief visits to nesting box from chickadee, wren, oak titmouse
Nest building Mar 6-16 Nesting material brought in, 19 to 174 trips per day
Egg laying Apr 5-10 Daytime away, nights on nest; 1 egg laid per day before sunrise
Incubation Apr 10-23 Most of day and all of night spent on nest
Hatching Apr 23-24 Most of day and all of night spent on nest; frequent feeding
Growing Apr 24-27 Frequent feeding and waste removal; rapid growth
Care-taking crisis Apr 27-29 Care-taking crisis results in the loss of the brood
New nesting attempt May 3 New nesting atttempt starts, eventually successful

April 27-29: Chickadee nestlings perish after care-taking crisis

This section contains links to disturbing videos for bird experts who might be able to determine the cause of the care-taking crisis. Viewer discretion is advised.

Something caused the chickadee mom to lash out at one of her nestlings on the evening of April 27 (see video at 5:24 PM). She soon settled down, returned the nestling to the nest cup, and went back to normal behavior.

The next morning, the mom had a health or behavioral crisis that caused her to tear out the top layers of the nest, cover the nestlings, and leave for half a day (see video at 6:25 AM). Two nestlings died as a result. That afternoon, the parents went back to normal care, feeding the remaining four and removing their waste.

That evening, however, the nestlings were left alone in the nest. By the next morning, April 29, all had died. The parents came back many times to try to feed them anyway.

April 25-27: Chickadee nestlings growing

Amber and Chester are busy feeding their nestlings and carrying away their waste during the day. At night, Amber sits on them. Each day they grow a little.

April 23-24: Chickadee eggs hatch

The eggs started hatching on the morning of April 23. By early afternoon, four eggs had hatched and both Amber and Chester were feeding them. The remaining two eggs hatched the next day, April 24

April 10-22: Chickadee incubates eggs

A sixth egg appeared on the morning of April 10. The chickadee mom "Amber" now spends most of the day on the nest, as well as all of the night (as she has been doing since April 1). During the day, she occasionally leaves the nest for 5 to 10 minutes, spending time with the chickadee dad "Chester". Upon return to the nest, Chester makes sure that Amber is safely back in the box. Occasionally he feeds her. I made the roof bigger and added some wire mesh to help keep out predators.

April 5-9: Chickadee lays eggs

The first egg became visible on April 6, one month after the start of nest building. While away from the nest, she kept the eggs hidden under a blanket of fluff. On the morning of April 7, she defended her three eggs from an invading snake, much to my surprise -- I didn't know we had any snakes in our suburban neighborhood! On April 9, she arranged her five eggs in the nest cup, surrounded by fluff, and began incubating them.

5 eggs

April 1-4: Chickadee spends nights on the nest

The chestnut-backed chickadee spent each night on the nest, entering the box around 7 PM and leaving the next morning around 7 AM. During the day, it visited the box on several occasions, sometimes sitting on the nest for 5 or 10 minutes, but spent most of its time away. A Bewick's wren entered the box several times, resulting in conflict.

March 21-31: Chickadee adding fluffy materials to nest

The chickadee spent the night on the nest March 20-21. It visited the nest during the day, sometimes bringing in more fluffy nesting material.

The Bewick's wren showed up in the afternoon of the 21st, the first time in 7 days, briefly entering and leaving the box; and again on the 22nd. The oak titmouse also spent a brief moment on the entrance hole.

I put up a second nesting box in the yard to attract the other birds. I'm hoping they will leave the chickadees alone and let them use the nest they spent so much time and effort building (600+ trips to bring in nesting material).

March 20: Chickadee occupies nest overnight

The chickadee spent the night in the nest for the first time, at the spring equinox. It entered the box half an hour before sundown and left it half an hour before sunrise. A 12-hour video record shows the bird preening and resting curled up in the nest.

During darkness, the video is in black-and-white due to infrared illumination from the camera. Like humans, birds cannot see infrared.

March 14-19: Chickadee completes nest

The chestnut-backed chickadee continued working on the nest on and off. The nest is complete or nearly so. The Bewick's wrens entered the box on the 14th but did not return after that, apparently learning that the box is taken. The chickadee returns to the box a few times per day.

March 12-13: Chickadee adds fluffy nesting materials; Bewick's wrens enter

The chestnut-backed chickadee starting adding fluffy materials over the redwood bark starting on March 12, including grass, white fluff (duck down?), animal fur, and what appears to be old bottle-brush flower filaments. On March 13, a pair of Bewick's wrens entered the box on several occasions, settling into the nest cup as if they had built it themselves. So far, the chickadee and wrens have not come into direct conflict, as they have been at the box at different times of day.

March 6-11: Chestnut-backed chickadee builds nest base of redwood bark

A chestnut-backed chickadee started bringing in new nesting material, thin strips of bark torn from a redwood tree 70 feet (20 m) away. It works very actively for periods ranging from 10 to 50 minutes, making a round trip every 1 minute to bring in and place a beakful of bark shreds. There are 3 to 5 such bursts of activity per day, starting around 8 to 10 AM and ending mid-day or early afternoon

From Cornell's All About Birds: "The female builds the nest on her own. She makes a bottom layer or foundation of moss and strips of bark. The nest's upper layer consists of animal fur woven with strips of bark, grass, feathers, and sometimes textile fibers. Adults also use fur to make a thin, warm flap to cover eggs when they leave the nest. Nest building takes 7 to 8 days."

Number of chickadee trips per day to bring in nesting material

March 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
# trips 19 35 74 49 60 174 97 53 20  2 19  8  2  3  1

Brief bird visits February 13 to March 6

   March 1 2 3 4 5 6
chickadee nest building starts

   February 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Feb 27: Chickadee removes a piece of snakeskin

chickadee removes snake skin
A chestnut-backed chickadee picks up a piece of snakeskin previously left in the nesting box by Bewick's wren, and throws it away. Does the chickadee intend to take over the box for nesting?

Feb 16: Chestnut-backed chickadees and Bewick's wrens visit

A pair of chestnut-backed chickadees visited multiple times, spending several minutes examining the entrance hole from the outside. A pair of Bewick's wrens visited once, bringing in one tuft of grass.

Feb 12: Oak titmouse enters box and takes a piece of snakeskin

oak titmouse returns
One of a pair of oak titmouse birds enters the box and takes a piece of snakeskin. This is the first oak titmouse entry since Jan 29. Which pair of birds will nest in the box, the Bewick's wrens or oak titmice? Or neither? Chestnut-backed chickadees nested there last year. Since last year, I added the camera, and two frosted acrylic windows to the sides of the box for better lighting.

Feb 11: Bewick's wrens return briefly and remove a sprig

removed a sprig
The Bewick's wrens returned briefly on February 11, 10, and 8. They removed a sprig of grass on the 11th and added a tuft of lichen on the 10th. There were no visitors at all on February 9.

Feb 7: Bewick's wren brings snake skin to box

snake skin piece
The Bewick's wren returns and places a piece of snake skin. I didn't know we had snakes in the area! It also repositioned what appears to be skin from a reptile tail. Earlier in the morning, it brought another piece of lichen.

Feb 5: Bewick's wren brings lichens into the box

nesting rituals video: lichens for nest
This pair of Bewick's wrens is considering whether to build a nest. One offers the other a sprig of grass; the other is reluctant to take it, as if the male is saying "Let's build a nest" and the female is answering "I'm not ready." Later in the day, the male started adding lichens and leaves to the box. The next day, February 6, it returned, moved some of the items, and left, spending just a minute in the box.

From Cornell's Bewick's Wren Life History: "The cup-shaped nest has a base of sticks, grasses, rootlets, leaves, moss, or other plant materials, depending on what the local environment provides. The open cup may be lined with feathers, wool, hair, or plant down, with a final inner lining of snakeskin. The male initiates nest building; both sexes participate. The construction process usually takes less than 8 days, though sometimes it can stall for long periods and require weeks to complete."

Feb 4: Bewick's wren pair returns for another inspection

video: return inspection
A Bewick's wren pair returns for another inspection after a 2-day absence.

Feb 2: Bewick's wren pair places nesting materials

video sprig of grass video clump of grass
A Bewick's wren pair places some dry grass in the nesting box. Nestwatch says that they nest from mid-April to early August. Are they reserving the box for later?

Jan 31: Bewick's wren checks out the box

video: bewick's
        wren first visit
Bewick's wren checks out the nesting box for 15 seconds. It came back for another brief visit the next day, February 1.

Jan 30: Chestnut-backed chickadee checks out the box

video: chickadee
        checks out box
A chestnut-backed chickadee checks out the box. This is the species that nested in the box in 2020. The brown chestnut color is found only on the back, not on the sides, from Marin County southward. Farther up north, the brown color extends down the sides.

Jan 29: Oak titmouse checks out the box

video: oak titmouse
        visits box
An oak titmouse checks out the bird box and clears out spider webs. It has a very small crest on its head.

The camera is a Green-Backyard IP bird box camera. I made a video showing how to use it. I made two acrylic windows to let in more light for the camera, as explained in another video. The exterior view comes from a Raspberry Pi camera card attached to an 8X monocular.

The entrance hole is 1-1/8 inches in diameter to exclude larger birds such as sparrows.

bird box camera bird nesting box Raspberry Pi camera monocular

Green-Backyard Bird Box Camera

Using the Green-Backyard bird box camera, you can capture, save, and view video using CMS5 software on PC. It uses natural illumination by day and infrared illumination at night.

You can capture live video as it is displayed on the PC and save it to a file on the PC. Alternatively, you can direct the camera to save video on an SD memory card in the camera itself, and later retrieve the video from the card. In either case, you can specify the time ranges in which to capture video.

If you are saving the video to the SD memory card, you can direct the camera to save video clips only when there is motion detected in the camera view. Thus, you can capture bird actions as they occur and skip recording when nothing is happening.

When you first power up the camera, be sure to set the exact time in the camera's clock so that you can easily locate video clips by clock time. The camera's clock does not run when the power is off.

I live-stream the bird box view to YouTube using the free OBS (Open Broadcaster Software) application. OBS allows you to mix multiple images, such as the bird box interior and exterior views, and to individually zoom, crop, and place the respective images. It also lets you mix audio sources, such as from the bird box and local microphone.

Bird Nesting Box Natural Illumination

Natural-light windows in a bird nesting box provide illumination for better webcam videos and might also encourage birds to select the box for nesting.

In this box, each window has a translucent piece of acrylic and a wire mesh. The frosty translucence helps distribute the light more evenly in the box and prevents predators from seeing into the box. The wire mesh might help birds feel more confident about deciding to nest in the box.

Bird preferences might depend on factors such as the amount of light, the sizes or shapes of the openings, and the bird species. The only way to find out for sure is to do a sufficient number of experiments. One scientific study showed that birds preferred nesting boxes with illumination.

If you have a camera inside the bird box, additional natural illumination improves the quality of daytime videos. In dark boxes that have only the bird access hole for light, the camera must boost the weak CCD image, resulting in optically noisy videos. Furthermore, the image is more susceptible to lens flare from extraneous light shining directly on the lens from the access opening, out of view of the camera.

By bringing in more light, the camera generates a better-quality, lower-noise image, and any lens flare has relatively less impact.

© Gray Chang 2021