Microclimate predicts within‐season distribution dynamics of montane forest birds

Abstract

Aim Climate changes are anticipated to have pervasive negative effects on biodiversity and are expected to necessitate widespread range shifts or contractions. Such projections are based upon the assumptions that (1) species respond primarily to broad‐scale climatic regimes, or (2) that variation in climate at fine spatial scales is less relevant at coarse spatial scales. However, in montane forest landscapes, high degrees of microclimate variability could influence occupancy dynamics and distributions of forest species. Using high‐resolution bird survey and under‐canopy air temperature data, we tested the hypothesis that the high vagility of most forest bird species combined with the heterogeneous thermal regime of mountain landscapes would enable them to adjust initial settlement decisions to track their thermal niches. Location Western Cascade Mountains, Oregon, USA. Methods We used dynamic occupancy models to test the degree to which microclimate affects the distribution patterns of forest birds in a heterogeneous mountain environment. In all models we statistically accounted for vegetation structure, vegetation composition and potential biases due to imperfect detection of birds. We generated spatial predictions of forest bird distributions in relation to microclimate and vegetation structure. Results Fine‐scale temperature metrics were strong predictors of bird distributions; effects of temperature on within‐season occupancy dynamics were as large or larger (1–1.7 times) than vegetation effects. Most species (86.7%) exhibited apparent within‐season occupancy dynamics. However, species were almost as likely to be warm associated (i.e., apparent settlement at warmer sites and/or vacancy at cooler sites; 53.3% of species) as cool associated (i.e., apparent settlement at cooler sites and/or vacancy at warmer sites; 46.7% of species), suggesting that microclimate preferences are species specific. Main conclusions High‐resolution temperature data increase the quality of predictions about avian distribution dynamics and should be included in efforts to project future distributions. We hypothesize that microclimate‐associated distribution patterns may reflect species' potential for behavioural buffering from climate change in montane forest environments.

A long‐term perspective on microclimate and spring plant phenology in the Western Cascades

“…While our study focused on herbs, shrubs, and trees native to the Western Cascades, the effect of advanced phenology is not limited to a single trophic level, and the negative effects of trophic asynchronies have been documented around the world (Walther et al 2002, Parmesan and Yohe 2003, Visser and Both 2005, Both et al 2009, Aldridge et al 2011, Forrest and Thomson 2011. Areas of topographic heterogeneity typically display a strong gradient in spring plant phenology (Hwang et al 2011), which may mitigate the effects of regional warming for mobile organisms like birds or mammals (Gaudry et al 2015, Frey et al 2016a). However, in 2015, a potential analogue of future winter weather and snowpack dynamics, the timing of spring plant phenology became much less varied across the landscape; it is possible that such loss of variation could lead to more widespread consequences and trophic asynchronies than in years in which early season microclimate and phenological diversity are maintained (e.g., 2011).…”

“…Our data suggest that in the Western Cascades (as opposed to the higher elevation High Cascades, which may not experience as great of a decrease in snow pack, Mote 2006, Mote et al 2018, years with snowpack well below average (Sproles et al 2017), and frequent anticyclonic weather patterns will have much greater effects on the mountain communities situated in upper elevation sites and sites of high topographic relief due to increased daily maxima (Appendix S1: Fig. Understory species are more likely to have significant shifts in phenology than overstory trees, and because sites with less vegetation biomass are less buffered against temperature extremes than sites with oldgrowth characteristics and high biomass (Frey et al 2016a), understory communities in upper elevation plantations (i.e., replanted secondgrowth timber stands) in the Western Cascades will likely have the greatest shifts in phenology due to changes in regional climate patterns. Understory species are more likely to have significant shifts in phenology than overstory trees, and because sites with less vegetation biomass are less buffered against temperature extremes than sites with oldgrowth characteristics and high biomass (Frey et al 2016a), understory communities in upper elevation plantations (i.e., replanted secondgrowth timber stands) in the Western Cascades will likely have the greatest shifts in phenology due to changes in regional climate patterns.…”

“…S1). Understory species are more likely to have significant shifts in phenology than overstory trees, and because sites with less vegetation biomass are less buffered against temperature extremes than sites with oldgrowth characteristics and high biomass (Frey et al 2016a), understory communities in upper elevation plantations (i.e., replanted secondgrowth timber stands) in the Western Cascades will likely have the greatest shifts in phenology due to changes in regional climate patterns. A recent study in the European Alps found a similar homogenization of phenological events, where bud break of four European trees advanced 1.9 d per decade from 1960 to 2016 at high elevations (>808 m), and only~0.4 d per decade at low elevations (<522 m; Vitasse et al 2018).…”

Synergistic effects of climate and land‐use change influence broad‐scale avian population declines

“…Although this approach does not allow us to assess marginal effects of, for example, early seral forest loss in conjunction with mature forest lost, the relatively small sample of counts within each landscape (i.e., maximum of 29 years) precluded a more highly parameterized model (Harrell, Lee, & Mark, ; Peduzzi, Concato, Kemper, Holford, & Feinstein, ). Furthermore, despite the high quality and fine resolution of our spatial data, recent work suggests that microclimatic factors (i.e., those at finer scales than can be assessed with satellite imagery) influence bird responses to climate (Betts, Phalan et al, ; Frey, Hadley, & Betts, ). Thus, other factors that were beyond the scope of our study are likely to have influenced bird population dynamics, but we restricted our focus to the factors we expected to be most influential over our study period.…”

Incorporating microclimate into species distribution models

“…In-situ measurements of temperature and other microhabitat characteristics -without interpolation -have additionally been shown to be valuable for descriptive distribution modelling at the local scale (Opedal et al 2015, Frey et al 2016. For example, strong correlations have been observed between changes in the frequency of plant species over time and the in-situ temperature of their preferred microhabitat on mountain summits in Switzerland (Kulonen et al 2018).…”