Speaking of Nature: Bill's bumper crop of bluebirds
Bill Danielson photo
The male bluebird delivers lunch to some hungry chicks.
Bill Danielson photo
A male eastern bluebird with a grasshopper.
Bill Danielson photo
This bluebird chick is three days old.
With mid-July behind us, it is now safe to say that the breeding season of our local songbirds is starting to wind down for the year. Some species, like the yellow warbler, may have already packed up for the season and started their move south. Others, like the red-winged blackbirds and grackles, still have hordes of hungry fledglings following them wherever they go. But here and there, if you look in the right places, you can still find birds that have tiny chicks in their nests.
One such place where these sorts of tiny birds can still be found is Box 21 on the western side of my yard. I mention the number of this nest box for anyone who read my column on June 12, in which I mentioned the locations and tenants of all the nest boxes in my yard. For those of you who didn’t see that column, the only thing you need to know is that Box 21 is in the center of a large area of lawn surrounded by a mix of trees and other lawns.
Because of its placement, Box 21 is a favorite of bluebirds and this year has seen the single most successful breeding season I have ever recorded for the birds that used my boxes. This year, Box 21 hosted a pair of eastern bluebirds who successfully raised and fledged two chicks on June 10. I was a little surprised that the female didn’t lay more than two eggs, but they both made it.
As the youngsters followed their parents about the yard, I went through the process of the mid-year purge and I visited every box that had fledged young and I removed the old nests. These are typically infested with various nest parasites and in the case of house wrens, the stick nests usually host a colony of ants. So, as is often the case with our own garage workshops, it is a good idea to clean everything out and get a fresh start.
The young bluebirds were constant features in the yard for most of June, but they eventually grew up enough to feed themselves and their frantic, panicked calling for assistance from their father slowly diminished. I was delighted, however, to discover that the adult male was still hanging around in the yard, so it got me to thinking that it might not be a bad idea to check on Box 21 again.
I was rewarded for this little idea when I discovered that the box not only contained a nest, but three new sky-blue eggs as well. Perhaps because the pair still had energy after raising only two chicks in their first clutch, or perhaps because it has been such a good year for nesting, the pair had gone for a second nest and I was delighted.
On Friday, July 11, the eggs hatched. At 10:30 in the morning, I looked into the box and found one tiny chick and two eggs. By that evening, there were three chicks and absolutely no sign of any of the eggshells. The quiet period of incubating eggs was over and the increasingly busy chore of feeding growing chicks was about to begin.
Today, even as I write this column, I can look out of the window in my office and watch the male coming and going with increasing frequency. I went down on Monday morning and discovered that the chicks had grown considerably. Their previously naked skin was now covered with a bluish-gray layer of baby feathers and their size had also increased tremendously. The only thing that hadn’t really happened as of Monday morning was their eyes hadn’t appeared to really open up. By next Monday, however, the chicks might be gone, so fast is the growth rate of baby birds.
The eastern bluebird (Sialia sialis) is another member of the thrush family Turdidae and is a cousin to the robin, which I wrote about last week. More delicate than the members of the genus Turdus, the members of the genus Sialia are also a bit smaller and a lot bluer. Blue is a rare color amongst birds and the Sialia use it to great advantage.
Unlike the colors red, yellow and brown, the color blue is not a result of pigmentation in feathers. Instead, blue feathers are the result of the mechanical bending and breaking of light, much like one would see in a prism or a rainbow. Light hits the feathers and the architecture of each barbule scatters the short wavelengths (blues and violet) so that we see them more intensely.
There are three species of bluebirds in the Sialia genus. In the summer, the eastern bluebird can be found from Maine to North Dakota and south to Florida and Texas. During the winter months, the northern birds retreat from the harshest conditions in the north and occupy a range with a northern limit that runs diagonally from Massachusetts to Texas.
The mountain bluebird’s (S. currucoides) range extends from North Dakota west to Alaska and then south to the U.S.-Mexican border. In winter, the mountain bluebird is confined to a much smaller range that falls mostly within California, Nevada, Arizona and New Mexico. Finally, there is the western bluebird (S. mexicana) that occupies a section of the western states concurrently with the mountain bluebird and is the only one of the three species (as its scientific name suggests) that ventures far down into Mexico during the winter.
The eastern bluebird is a member of our avian community throughout the year and I have personally recorded them during every month. Despite the fact that they are always present, they are never what I would consider abundant. In fact, this species has suffered greatly because of the introduction of house sparrows and European starlings. However, the decision by many concerned birders to build bluebird trails (large numbers of bluebird nest boxes that are maintained by people) has greatly helped this species.
This is because bluebirds are cavity nesters, which means they like to nest inside trees. The problem is that both house sparrows and European starlings are also cavity nesters and both species are larger and more aggressive than bluebirds. As a result, the invaders dominate most of the natural cavities.
Man-made cavities (nest boxes) are just as acceptable to the bluebirds and they have the added bonus of some measure of protection from the invasive sparrows and starlings. Humans can monitor the boxes, discourage the invaders and tilt the balance back in favor of the bluebirds. The reward is simple: more and more bluebirds.
Bluebirds will not nest just anywhere. If you have a yard that is large and open, resembling a pasture, hay field, or even a golf course, then you may get lucky. Smaller, wooded yards will not attract bluebirds even if you put out the boxes. This can be greatly disappointing, but you can’t make the birds nest where they can’t make a living.
If you’d like more information on building bluebird boxes, or how to control house sparrows, please visit the Readers’ Corner page of my website.
Bill Danielson has worked as a naturalist for 16 years. In that time, he has been a national park ranger, a wildlife biologist and a field researcher. He currently works as a high school chemistry and biology teacher. His Speaking of Nature column runs weekly in The Recorder, except for the first Thursday of each month, which is when his Kids and Critters column for young readers appears. To contact Bill, or to learn more about his writing, visit www.speakingofnature.com