Black-capped Chickadee female. Photo by Kathy, May 2010
Kathy of NY (AKA nybluebirdfan) photographed this nest with two Black-capped Chickadee eggs and four Eastern Bluebird eggs. It is not known which bird laid the first egg, but it was probably the chickadee, as they tend to nest earlier, and when Kathy first noticed this there were only three bluebird eggs. The female bluebird incubated all 6 eggs. Only the bluebird eggs hatched (on May 6, 2010.)
The nest was a made with dried grass, like a typical bluebird nest, but lined with hair like a chickadee nest. Both species were seen coming in and out of the Gilwood box early on, but the bluebirds eventually won out (as they almost always do.)
I heard numerous reports in early 2010 of bluebirds and chickadees competing for nests - chickadees usually started first, and then bluebirds win.
Eastern Bluebirds incubate for about 12-14 days (can be 11-19). The babies stay in the nest about 17-18 days (can be 19-21).
For chickadees (black-capped, assume others are similar) incubation is typically 12-13 days, and fledging is around day 16.
So...the timing is pretty similar. In a situation like this, I would not interfere and just let it play out.
Bluebirds seem very attracted to Gilwood boxes. Chickadees also tend to like boxes with a small interior like the Gilwood, the Gilbertson, and a small NABS-style box. There are a number of other boxes available on the property.
If you have birds fighting over boxes, please do try putting up a second nestbox. However, often neither bird wants to give up.
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