Chestnut-backed chickadees live on the west coast of North America from Alaska to Southern California. They are common in parks and suburbs of the San Francisco Bay Area, where I have this backyard nesting box.
The female 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.
When ready, she lays one egg each night until she has a clutch of five or six. When she starts incubating them, she goes outside only to eat and drink. Her mate sometimes brings her food.
After 2 weeks of incubation, the first egg hatches. Initially the chicks are blind but not deaf. Both parents feed them frequently, chirping to let them know when food has arrived. The nestlings grow quickly and fledge about 3 weeks after hatching.
Spring 2023 chickadee nesting timeline:
Nest building started March 30
Night roosting started April 1
Egg laying started April 13
Nest abandoned with 6 eggs for unknown reasons April 19
Nest building restarted April 24: Nesting material brought in, up to 200 trips per day
Night roosting started April 25: Daytime away, nights on nest
Egg laying restarted April 30: Daytime away, nights on nest; 1 egg laid per day
Incubation May 4-17: Most of day and all night on nest
Hatching: May 17-18: Most of day and all of night spent on nest
Fledging: June 9: Young fly away from the nest
Spring 2022 (last year's) chickadee nest timeline:
Nest building Mar 4-9
Roosting starts Mar 9
Egg laying Mar 21-26
Incubation Mar 26 - Apr 9
Hatching Apr 8-9
Fledging May 1
New nest building: May 19-21
Egg laying: May 27-30 (4 eggs)
Incubation started: May 25
Hatching: June 12 (2 eggs hatched)
Nestlings died: June 22 & 25
I think last year's late-season nesting attempt failed because of the drought. There was not enough food to be found to keep the 4 nestlings fed and hydrated. They did better this year with the abundant rain, foliage, and insects.