Regional patterns of diurnal breeding bird communities in Oregon and Washington

Breeding bird communities surveyed in 132 natural fire-regenerated Douglas-fir forest stands were examined fordifferences in species richness and abundance among foreststand age-classes: young, 35 to 79 years old, n = 27; mature,80 to 190 years old, n = 37; and old-growth, 200 to 730 yearsold, n = 68, and among physiographic provinces: OregonCoast Range (1985 and 1986, n = 45); Oregon CascadeRange, 1984 and 1985, n = 48 and 15, respectively; andsouthern Washington Cascade Range, 1984 and 1985, n = 39.Stands were surveyed six times each spring using 8-minutecounts at 12 counting stations spaced 150 or 100 m apart.More than 115,000 birds were detected. We counted 41 spe-cies that regularly used Douglas-fir forests >40 years old,after the exclusion of raptorial, nocturnal, and poorly detectedspecies. The most widespread and abundant species werechestnut-backed chickadee, western flycatcher, winter wren,hermit and Townsend's warblers, and golden-crowned king-let. All bird species significantly more abundant in forests>80 years old in at least two of three regions at P Results suggested that patterns of bird abundance were re-gionally distinct, even though the study design differed be-tween regions. Total bird abundance, species richness, andbird abundance in four spatial-foraging guilds (aerial, bark,canopy, and understory) were significantly higher in the
Oregon Coast Ranges than in the southern Washington orOregon Cascade Range. Aerial and bark guilds showedstrong differences among age-classes: the aerial guild reachedits highest abundance in young and old growth and the barkguild was least abundant in young and highest in old growth.Vegetation characteristics used for multiple linear regressionmodels predicted only a small proportion of the variance inbird abundance.