Abstract
Deviations from typical environmental conditions can provide insight into how organisms may respond to future weather extremes predicted by climate modeling. During an episodic and multimonth heat wave event (i.e., ambient temperature up to 43.4°C), we studied the thermal ecology of a ground‐dwelling bird species in Western Oklahoma, USA. Specifically, we measured black bulb temperature (T bb) and vegetation parameters at northern bobwhite (Colinus virginianus; hereafter bobwhite) adult and brood locations as well as at stratified random points in the study area. On the hottest days (i.e., ≥39°C), adults and broods obtained thermal refuge using tall woody cover that remained on average up to 16.51°C cooler than random sites on the landscape which reached >57°C. We also found that refuge sites used by bobwhites moderated thermal conditions by more than twofold compared to stratified random sites on the landscape but that T bb commonly exceeded thermal stress thresholds for bobwhites (39°C) for several hours of the day within thermal refuges. The serendipitous high heat conditions captured in our study represent extreme heat for our study region as well as thermal stress for our study species, and subsequently allowed us to assess ground‐dwelling bird responses to temperatures that are predicted to become more common in the future. Our findings confirm the critical importance of tall woody cover for moderating temperatures and functioning as important islands of thermal refuge for ground‐dwelling birds, especially during extreme heat. However, the potential for extreme heat loads within thermal refuges that we observed (albeit much less extreme than the landscape) indicates that the functionality of tall woody cover to mitigate heat extremes may be increasingly limited in the future, thereby reinforcing predictions that climate change represents a clear and present danger for these species.
Highlights
Comparatively rare, extreme climatic events can have substantial impacts on populations (Easterling et al, 2000; Holmgren et al., 2006; Parmesan, Root, & Willig, 2000)
By capturing periods of high ambient temperatures which represented extreme heat for our study region and thermal stress for our study species, we demonstrate how a local resident species responds
Our results agree with findings from previous studies that have shown the thermal importance of tall woody cover for ground-dwelling birds (Goldstein, 1984; Martin et al, 2015; McKechnie et al, 2012), but most importantly, showcases how tall woody cover functions as critical islands of thermal refuge during extreme heat
Summary
Extreme climatic events can have substantial impacts on populations (Easterling et al, 2000; Holmgren et al., 2006; Parmesan, Root, & Willig, 2000). Assessing how microhabitats buffer thermal extremes will be important for linking changes in climate to changes in microclimate (Goller, Goller, & French, 2014; Potter, Arthur Woods, & Pincebourde, 2013; Scheffers et al, 2014) and can provide perspectives that are more relevant to organisms than approaches that assess thermal conditions at broader scales (e.g., >1 km) (Gunderson & Leal, 2012; Hannah et al, 2014; Helmuth et al, 2010; Sears et al 2011). Our secondary objective was to use bobwhites as a model species to estimate thermal buffering at refuge sites and validate future heat load predictions for ground-dwelling birds. We aimed to evaluate the capacity of thermal refuges to continue to modulate microclimate in the future
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