Abstract
Recently, gaining knowledge about thermal refuges for vulnerable species has been a major focal point of ecological studies, and this focus has been heightened by predicted temperature increases associated with global climate change. To better understand how organisms respond to thermal landscapes and extremes, we investigated the thermal ecology of a gallinaceous bird species (northern bobwhite; Colinus virginianus, hereafter bobwhite) during a key life history period. Specifically, our study focused on the brood‐rearing period of precocial bobwhite chicks associated with brood‐attending adults. We measured site‐specific black bulb temperatures (Tbb) and vegetation characteristics across 38 brood tracking days and 68 random landscape sites to assess thermal patterns at scales relevant to broods. We observed that the landscape was thermally heterogeneous, exhibiting variation in Tbb up to 40°C during peak diurnal heating demonstrating a wide array of thermal choices available to broods. At 15:00 h, broods selected thermal refuges that moderated Tbb on average up to 10.4°C more than landscape sites. Moreover, broods exhibited behavioral thermoregulation through reduced movement and by occupying more moderate microclimates that afforded taller vegetation structure during high heat. Modeled climate projections suggest that future Tbb in thermal refuges will approach those currently avoided on the landscape, emphasizing the need for future conservation plans that acknowledge fine scale thermal space in climate change scenarios. These findings underline that studying both abiotic and biotic factors at scales relevant to organisms can increase our understanding of how thermally heterogeneous landscapes provide thermal choices under extreme conditions.
Highlights
Thermal environments impact all organisms on Earth (Brock 1967, Angilletta 2009), and are a primary component of a population’s fundamental niche (Hutchinson 1957, Magnuson et al 1979, Kearney and Porter 2004)
Analyses To characterize thermal conditions relevant to broods, we modeled site specific Tbb for brood locations and random landscape sites relative to Tair and solar radiation (Srad) recorded at onsite weather stations using regression analysis
We found highly heterogeneous thermal environments with variations in Tbb by up to 408C, indicating a wide array of thermal choices available to organisms within diurnal periods
Summary
Thermal environments impact all organisms on Earth (Brock 1967, Angilletta 2009), and are a primary component of a population’s fundamental niche (Hutchinson 1957, Magnuson et al 1979, Kearney and Porter 2004). If thermally buffered microsites cannot be obtained, extreme heat exposure can cause body temperature to reach lethal limits if heat load surpasses the animals thermoregulatory capacity for heat dissipation (Cowles and Bogert 1944, Porter and Gates 1969, Cunningham et al 2013a). Air temperatures of large portions of landscapes in both semi-arid and subtropical regions can exceed lethal thermal thresholds for birds during hot conditions (Goldstein 1984, Guthery et al 2001). A better understanding of how landscapes moderate thermal environments, as well as how organisms exploit thermally buffered sites (i.e., refuge), will be a critical component of species conservation especially in light of future climate change (Hovick et al 2014)
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