A few years ago, a volunteer built and put up a bluebird nesting box outside the Ecology Center's office. I have to admit I was a bit skeptical. As if to prove my point, that box sat vacant throughout the entire breeding season. Soon after, I noticed several people and organizations promoting them, and wondered whether this was just a another fad.

A year later, a pair of violet-green swallows found their way to the "bluebird" box, and raised their young. Even if they were the wrong color, I was delighted. In the punctual way that swallows have, the family returned the following year, and again this year. This year there was a difference, though. A pair of bluebirds had finally found the box, and were making preparations to use it. The resulting contest was interesting. Despite superior numbers and agility and speed of the swallows, the two bluebirds held on in a calm, determined way, and were successful in hatching their young. Some faceless, pleading mouths are now taking shape into animals that actually resemble birds, and I am beginning to believe that this now well-worn bluebird box may actually work.

The western bluebird, Sialia mexicana, has a visable population our area. I've seen them frequently at Sonoma Valley Regional Park. In recent years as with many native species, western bluebird numbers have fallen, though they may be making a slight comeback, thanks in part to nesting boxes. The western bluebird belongs to the family Turdidae, the thrushes, which includes some familiar birds such as the American robin. Unlike their eastern bluebird relations who favor open meadows for nesting, these bluebirds prefer forest edges of pine or oak woodland. They typically raise their young in cavities left by woodpeckers in the snags of old trees and it is the loss of this habitat that has caused their decline.

Like the violet-green swallows, bluebirds eat large numbers of insects -- about 80 percent or more of their diet. It is fascinating to see the different strategies each bird uses to catch insects. Swallows move in a high paced, acrobatic flight for most of their waking hours it seems, and they perform steep banked turns and tucks to take insects on the wing. Bluebirds seem to casually flit away from a perch and grab an insect in the air or a caterpillar off the ground in a quick gesture that makes the entire project seem simple and not worth the energy to do it otherwise. This diet is one of the more important reasons for encouraging bluebirds and their nesting boxes in our area. They provide a natural check on agricultural pests.

All thrushes tend to eat insects. Most also eat fruit or berries, especially after the breeding season. Mistletoe berries are a favorite of the bluebird. While other birds are heading down to warmer areas in fall and winter, western bluebirds may go uphill into the mountains until these berries are gone. There is speculation that the bluebird may be one of the more significant agents for dispersing the seeds of the mistletoe.

Bluebirds typically have two "broods", or groups of young in a year, about four or five in each. The second is begun at the time the first brood has its feathers or is "fledging" and is ready to leave the nest. The entire family will stay together until fall. By winter, bluebirds will form into small flocks that search out food or water. There is some evidence that they establish regular routes to search out food. By spring, the bluebirds will be back seeking nesting sites. If you want to have a nesting box, Hanna Boys Center has created a small program to manufacture them and provide a source of some income. Contact their office at 996-6767.