Nest Site Selection in Mountain Bluebirds

-Nest site selection was analyzed for a Mountain Bluebird (Sialia currucoides) population using two different types of nest box in southcentral Washington. The majority of adult females successful in fledging young during the previous year either returned to the same territory and nest box or selected the same type of nest box if they changed territories. If they were unsuccessful, adult females tended to change territories and box types. Most male and female bluebirds breeding for the first time selected the same type of box as housed their natal nest even though none of these birds returned to its natal territory. Nest site selection and breeding area fidelity were influenced by age, sex, previous breeding experience, and natal nest type. Recently, Cink (1976) examined the degree to which nestling House Sparrows (Passer domesticus) imprinted on the type of structure housing their natal nest. Although he found no evidence that early learning or imprinting had any effect on nest site selection, females tended to choose hole-type nests over open nests. Other studies have shown that some species prefer a larger to a smaller nest box (Jiirvinen 1978) and that floor dimensions of a box can influence clutch size (Karlsson and Nilsson 1977). Jackson and Tate (1974) analyzed selection of artificial nest sites by Purple Martins (Progne subis), House Sparrows, and Starlings (Sturnus vulgaris) and found only slight differences related to interior and exterior colors, location, and materials from which the boxes were constructed. Lumsden (1976) reported that Starlings preferred small entrance holes and dark interiors. Bluebirds, like all cavity-nesting species, are limited by availability of suitable nest sites. Many studies (e.g., Miller 1970, Power 1974) have shown that bluebird populations can be increased by placement of nest boxes in suitable habitat. Although much is known about the reproductive biology of bluebird populations (Power 1966, Peakall 1970, White and Woolfenden 1973, Pinkowski 1977a, 1979a), little has been published concerning nest box selection and breeding area fidelity (the tendency for birds to return to the territory used the previous breeding season). Pinkowski (1979b) analyzed breeding data for Eastern Bluebirds (Sialia sialis) using artificial and natural nest cavities and found that age and nesting success seemed to be the most important factors influencing nest site selection. Additionally, he concluded that imprinting on the natal type of nest site was not important. I theorized that imprinting on the natal type of nest site would be important for secondary cavity-nesting species because of the scarcity of natural cavities and that species-specific differences could influence nest site selection. To test these theories, I examined breeding data for a Mountain Bluebird (Sialia currucoides) population using two different types of nest box and analyzed the influences of age, sex, previous breeding experience, and natal nest type on nest site selection. STUDY AREA AND METHODS The study area was located south of Bickleton and Cleveland, Klickitat County, Washington. Elevation ranges from 915 m near Bickleton on the north to 701 m in valleys running north-south. The northern edge of the study area is on the ecotone between ponderosa pine-Oregon white oak (Pinus ponderosa-Quercus garryana) forest and big sagebrush-bluebunch wheatgrass (Artemisia tridentata-Agropyron spicatum) steppe. Much of the land south of Bickleton and Cleveland is farmed with winter and spring wheat and with barley. Areas not cultivated are moderately grazed by cattle. The two types of nest box were designated as either "old" or "new" indicating how long they had been present on the study area. The "old" boxes were first erected in 1966 and new boxes were added each year (J. Brinkerhoff, pers. comm.). These boxes resembled a small house with a peaked roof. The inside dimensions of the floor were 30 x 15 cm with an entrance hole diameter of 4.4 cm; the entrance hole was approximately 10 cm above the floor. The outside of these boxes had a blue roof and white sides; the interiors were not painted. All of the "new" boxes had inside floor dimensions of 12.7 x 12.7 cm with a 3.8-cm diameter entrance hole, the bottom of which was 14 cm from the floor. The "new" boxes were not painted. Both "old" and "new" boxes were made of wood. The number of "old" box types available was usually 50 (except for 41 in 1976) and "new" box types numbered 30-31. "Old" type boxes were placed on top of wooden fence posts and "new" type boxes were nailed to the