Well, it is nesting season and being a nest box monitor with three Bluebird Trails, I thought I should rectify the blatant lack of coverage on 10,000 Birds of one of the most iconic North American birds of our time. Living in California, I am of course speaking of the Western Bluebird (Sialia mexicana).
The Western Bluebird, like all bluebirds, is a secondary cavity nester (more about cavity nesters in an upcoming post). They nest in cavities, created by woodpeckers, in large trees and snags. This is the male Western Bluebird checking out a natural cavity in a large oak tree (click on photos for full sized images).
Unfortunately, Western Bluebird populations have been declining because of habitat degradation (loss of suitable nest sites and foraging areas) due to extensive logging, natural-fire suppression, grazing, industrialization, and urbanization1.
Fortunately, bluebirds will also accept artificial nest boxes, which several organizations like the North American Bluebird Society and individuals across the country provide in the form of bluebird trails or backyard birdhouses. Above is the male Western Bluebird and below the female at the entrance to a nest box or birdhouse.
This entire cycle begins in early Spring when Western Bluebirds pair up for breeding. Even though they are socially monogamous, they also seek matings outside the pair bond, with the result that offspring are not always related to the attendant male1.
The pair may have to compete for nesting cavities with several other species including native Tree Swallows and Violet-green Swallows, as well as non-native House Sparrows and European Starlings. This may have also contributed to the decline in Western Bluebird numbers in the Northwest.
Like Tree Swallows, the happy couple like to stake out their nest site by perching on their chosen home.
Northern California sees Western Bluebird nest building activities beginning as early as March. The nest is a cup of dry grasses and sometimes a few feathers, built by the female, the male is occasionally seen with a blade of dry grass in his beak but his contribution is purely symbolic.
The female alone incubates the usual 4 to 6 eggs for about two weeks beginning the day the last egg is laid.
Here you can see two chicks have already hatched, one egg is split open with the chick ready to emerge and one egg has a hole in it pipped by the chick from the inside.
A couple of days later the chicks have soft gray down on their heads and along their spine but their eyes aren’t open yet, they’re just slits.
At about a week of age, the nestlings begin to open their eyes and their feather sheaths are evident.
A week later they are fully feathered, the male having brighter blue feathers than the female.
At this point, we no longer want to open the nest box as this may prompt premature fledging by the nestlings. This is one reason that if you do have nest boxes, even if it is only one birdhouse in your yard, it is important to monitor it closely and keep good records. You can download a Nest Box Monitoring Guide from my website.
The average day for young Western Bluebirds to fledge is at 21 days of age. If you know when the chicks were hatched and exactly how old they are, you may get to see their first flight from the nest.
As you may have noticed in the video, the parents try to coax the nestlings out of the nest box by perching on nearby branches and calling to them. They also do “mock feedings’ where they act as if they are bringing food to the nest, then fly to a branch and call.
The parents continue to feed the young after fledging. For the first 3–5 days post-fledging, the young fledglings are almost completely dependent on the adults for food. After about two weeks however, they are independent and able to feed themselves.
I found these youngsters with their parents on one of my Bluebird Trails. They were old enough to feed themselves, flying down to the ground to pick on whatever they could find.
They were young enough that they were still sticking together and playing with each other.
This could be the runt with an older chick. They were fun to watch.
When dad flew by with some food, it was the youngest chick that had the biggest gape. But I didn’t see them being fed. He just flew to another tree where the chicks followed.
With the help of Bluebird Trails and backyard birdhouses and maybe a change in logging practices in the West, we can continue to see an increase in Western Bluebirds out West. They are listed as sensitive in Oregon and Utah; a candidate for listing in Washington and a species of high concern by New Mexico Partners in Flight. Western Bluebirds are also considered “in jeopardy” in California and are proposed for designation as a species of “special concern” in British Columbia1.
One of our greatest success stories in the fight to return Western Bluebirds to their native habitats occurred in Washington’s San Juan Islands where they were absent for forty years. You can read the story ” Washington Western Bluebird Reintroduction Effort a Success!” at the American Bird Conservancy’s website.
Until next time, I leave you with the late Israel Ka?ano?i Kamakawiwo?ole’s beautiful rendition of “Somewhere Over the Rainbow.” Have a great Fourth of July!
References:1Birds of North America Online