Western Bluebird Nest-site Characteristics in Managed Ponderosa Pine Forests

We studied the nest-site characteristics of Western Bluebirds nesting in natural tree cavities in burned and unburned logged ponderosa pine forests along the east-slope of the Cascade Range of Washington, 2003–2008 and 2010. We compared 13 bluebird nest-site habitat variables between burned and unburned stands by assessing overlap in 95% CI. Tree density (number of live trees >25.4 cm diameter at breast height/ha) and percent debris cover (litter and large woody debris) were greater at nest sites in unburned stands and they were the only nest-site characteristics that differed between the two treatments. Cavity orientation in burned stands was not uniformly distributed and the mean direction was 121 degrees; whereas cavity orientation in unburned stands was uniformly distributed. Ponderosa pine contained the most cavities (82%) followed by Douglas-fir (11%), while the majority of substrates containing bluebird nest cavities (73%) had advanced decay and broken tops. Of the cavities bluebirds used where the original excavator was known, 27% were excavated by Hairy Woodpeckers, 12% by White-headed Woodpeckers, and 5% by Northern Flickers. Only one nest was located in a non-excavated cavity. Of the 38 second nest attempts, 76% occurred in the same cavity as the first attempt even though 38% of these first attempts were unsuccessful. Our results suggest that bluebirds are using similar nest sites in burned and unburned ponderosa pine stands and that they rely almost entirely on primary excavators to create the cavities they use for nesting.