Western Bluebird in a clear cut, Hayward, Washington Co., Oregon on 16 May 2008 by Greg Gillson.When I began birding in 1972 the Western Bluebird was near the bottom of a 30-year decline in population in western Oregon countrysides. In fact, they were nearly extirpated. For instance, winter bird censuses for the Portland Christmas Bird Counts (CBC) from 1935-1947 averaged 20 birds per year, with a high of 47 and a low of 5. From 1966-1976 not a single bluebird was recorded on the Portland CBC (Hubert Prescott, Portland Bluebird Trail, SWOC Talk, Vol 3, No. 2. 1977).
Causes of decline are complex, controversial, and not fully understood. Certainly the spread of House Sparrows in the Pacific NW from the late 1890's was a large factor. The demise of family farms and the conversion to larger edge-to-edge farming played a role, as did the conversion of farmland into residential suburbs. Widespread use of insecticides may have played a role after World War II from 1945, eliminating insects or causing harm to birds eating treated insects. Then, too, the European Starlings could also have hurried the bluebird's downfall after they arrived in western Oregon in the 1940's. Forest practices, namely clear cutting with complete snag removal, made the foothills unattractive to bluebirds.
There were a very few bluebirds remaining, however, on farms on some of the small hills in the Willamette Valley. From 1974-1976 Bluebird Trails started up in rural areas near Portland, Salem, Corvallis, Eugene, and elsewhere. Volunteers built and placed hundreds of bluebird boxes at regularly spaced intervals across rural areas, starting at known nesting sites. Small diameter entrance holes kept out Starlings and most House Sparrows. But Violet-green Swallows, Black-capped Chickadees, House Wrens, Bewick's Wrens and other cavity nesting birds competed for these boxes. And predation and vandalism was high. Nevertheless, bluebird numbers climbed.
Numbers have not recovered on the Portland CBC. Perhaps, because of the urban sprawl, bluebirds will never return to backyards in Portland. But in Corvallis, some comparisons can be made. The first 5 years of counts in Corvallis, 1963-1967, this count averaged 24 birds. The population crashed, perhaps due to disease and a harsh winter, in 1969. During a couple of subsequent years no bluebirds were found. In the 5 years after the Corvallis Bluebird Trail was started, 1976-1980, Corvallis averaged 54 bluebirds on the CBC. In the most recent 5-year period, 2003-2007, the average number of Western Blubirds on the Corvallis CBC was 263. Amazing!
More and more people in the general public are erecting specially designed bluebird nest boxes. Forest practices have changed a bit so that some standing snags are left after timber harvest. Bluebirds nest in old woodpecker holes in these snags out in the middle of a clear cut in the lower Coast Range and Cascade forests. And bluebirds are increasing because of it.
In the Pacific Northwest, Western Bluebirds occur in lowland farmlands with scattered trees away from European Starlings west of the Cascades in Oregon and Washington. They also like open pine forests on the east slope of the Cascades of Oregon and Washington and higher mountians of NE Oregon, SE Washington, northern Washington and Idaho. They like oak savannah and open dry woods in SW Oregon and northern California.