Spring and Winter Bird Populations in a Douglas-Fir Forest Sere

Abstract

Changes in bird species richness, abundance, and guild structure were compared among young (42-75), mature (105-165), and oldgrowth (250-500+ years) and between winter and spring, for 2 years in Douglas-fir (Pseudotsuga menziesii) forests of the southern Washington Cascade Mountains [USA]. In winter, bird species richness, diversity, and abundance were all greater in oldgrowth than in younger stands. The most abundant species were the chestnut-backed chickadee (Parus rufescens), golden-crowned kinglet (Regulus satrapa), pine siskin (Carduelis pinus), and red crossbill (Loxia curvirostra). In spring, there were few differences in diversity and abundance along the stand age gradient. Species richness showed a slight increase from young to oldgrowth. The most abundant spring species were the winter wren (Troglodytes troglodytes) western flycatcher (Empidonax difficilis) varied thrush (Ixoreus naevius), hermit warbler (Dendroica occidentalis), and chestnut-backed chickadee. The Vaux''s swift (Chaetura vauxi) exhibited the strongest association with oldgrowth in the spring. Seasonal changes in abundance were greater in young and mature stands than in oldgrowth. This pattern was most noticeable among permanent resident species. A more favorable microclimate and probably better foraging conditions in oldgrowth in winter may explain the observed seasonal patterns of abundance.