Chestnut-Backed Chickadee Nesting Calendar, SF Bay Area
Historical Dates for Nest-Building, Egg-Laying, Hatching, Fledging; SF Bay South Peninsula
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. The following chart shows the season timing of their activity over the past few years.
Inconsistent seasonal schedule
As you can see in the chart, there was no consistency from year to year for the date on which nest building and incubation started. This could be due to the weather.
The birds may prefer to start nesting after the winter rains have subsided, and they need plenty of lush vegetation (fed by the rain) to support an abundance of insects and spiders to feed their young. 2022 was a very dry year, when nesting started early in the season, whereas 2023 was a very wet year, when nesting started late.
Failed nesting attempts
Half of the nesting attempts ended in failure, resulting in the loss of all eggs or nestlings. The cause was different each year.
2021: When the hatchlings were five days old, the mother chickadee had a behavioral crisis. She lashed out at her young, messed up the nest, and abandoned them. She resumed normal behavior a day and a half later and tried to feed them. However, they could not survive the gap in care and died shortly after that. A few days later, the parents started over from scratch, making a new nest, and successfully raised four nestlings.
2022: The chickadee pair got an early start in the season and successfully raised five nestlings that fledged on May 1. In mid-May they attempted a late-season nest. Four eggs were laid and two hatched. However, in this drought year, there were very few green plants in June and therefore few bugs available for food. The two nestlings died of dehydration/starvation.
2023: The parents abandoned a full clutch of six eggs without starting incubation. Perhaps the eggs were not viable. A week later, they (or maybe a different pair) started fresh, building a new nest on top of the abandoned eggs, and successfully raised six nestlings.
2024: The female laid an egg but left it uncovered. She returned to the nest in the evening as expected but perched next to the nest cup instead of sitting in it. In the morning she was obviously ill and died shortly thereafter. One viewer said it was a case of "egg binding." When I cleaned out the nest, I found five more eggs hidden under the fluff, so she had laid a full clutch of six but died before she could start incubation.
