Microclimate driven by complex terrain predicts within-season movement by a migrant songbird

Current predictions about species sensitivity to climate change are primarily based on ‘bioclimatic envelope models.’ These models assume that species either shift their geographic ranges to match underlying macroclimate, or they go locally extinct where macroclimate is no longer suitable. The degree to which species' behavior can mediate these possibilities is not well known. For instance, microclimate variability in complex terrain could buffer against climate changes by providing local options for short, adaptive movements and resource tracking. We assessed the potential for Hermit Warblers (Setophaga occidentalis) to behaviorally adapt to microclimatic changes; we examined their within-season movements at the H.J. Andrews Forest in the Oregon Cascades. Avian point counts were conducted at 184 sites during six distinct sampling periods from May – July 2010. Local temperature was monitored at 56 sites. We used dynamic occupancy models to estimate probability of detection, site occupancy, settlement, and vacancy. We investigated the effect of elevation (a proxy for temperature) on within-season movement. The effect of elevation on settlement and vacancy varied by sampling period, most notably flipping from positive to negative between mid- and late-May, corresponding with a drop in mean weekly temperature. We also found that sites that were more buffered from temperature changes throughout the season had a lower vacancy probability, whereas sites with larger changes in temperature were more likely to be vacated. These preliminary results indicate that birds may be capable of responding to changes in macroclimate within a breeding season by shifting territories to capitalize on buffered microclimates in complex terrain.