Ground surface vs. black globe temperature in northern bobwhite resource selection

Abstract

Understanding thermal ecology of endotherms is becoming increasingly important with predicted increases in temperature associated with climate change. Patterns of resource selection may depend in part on temperature thresholds outside which animals avoid warmer or cooler temperatures. During summer, northern bobwhites (Colinus virginianus; hereafter bobwhite) in semiarid areas often exist at the limits of their thermal tolerance. We sought to determine (1) selection bounds for black globe and ground surface temperatures, (2) whether ground surface temperature is a better predictor of the thermal environment used by bobwhites than black globe temperature, and (3) how time of the day influences thermal resource use. We radio‐marked 40 bobwhites and located them two to three times a week from April to September in 2014–2016. At each location, we measured ground surface and black globe temperatures at the bird location and at a location 20 m away in a random direction. We calculated continuous selection functions to estimate bounds of thermal characteristics suitable for bobwhites. We used generalized linear models to determine times of day bobwhites select cooler microclimates. Finally, we used case‐controlled logistic regression models to generate thermal resource selection functions. We compared models that included ground surface temperature, black globe temperature, and an index created from both variables with principal component analysis and selected the best model based on Akaike's information criterion adjusted for sample size (AICc) and log‐evidence ratios. Upper and lower selection bounds for black globe temperature and ground surface temperature were 24.5–42.5°C and 23.0–39.5°C, respectively. A principal component of black globe combined with ground surface temperature was a better predictor of bobwhite resource selection than either black globe temperature or ground surface temperature alone. In early afternoon (13:01–17:30 hours) during August, bobwhite locations had 13°C cooler black globe temperatures and 18°C cooler ground surface temperatures than random locations. Availability of thermally usable coverts (woody plant thickets) may be a limiting factor for bobwhites in the study area based on the findings that mean ground surface and black globe temperatures at used locations were close to the upper bounds for use in late summer during the middle of the day.

Resource selection of a montane endemic: Sex-specific differences in white-bellied voles (Microtus longicaudus leucophaeus)

“…To minimize the effect of our presence on vole movement we waited one hour to collect vegetation data at the location, given the vole had moved away from that location. We collected vegetation data at two points: the vole's known location and at a paired, randomly generated location [14,45]. Random locations were placed 9.8 m away from the vole's known location, which we based on the average hourly movement rate of other vole species [42,[46][47][48].…”

Temperature influences resource use by chestnut‐bellied scaled quail

“…For northern bobwhites, a combination of ground surface temperature and black globe temperature was a better predictor of the relative probability of use than either of the temperature measurements alone (Olsen et al. ). Based on these results, we encourage investigators researching the effects of temperature on habitat selection behavior by animals, particularly species in constant contact with the ground, to consider including measurements of ground surface temperature.…”

“…Ground surface temperatures have been widely used in habitat selection studies of ectotherms (Kapfer et al 2008, Sato et al 2014, Smith et al 2015b, Ahnesj€ o and Forsman 2006 and have been less widely used in studies of endotherms such as ground-dwelling mammals (Sharpe and Van Horne 1999) and desert birds (Tieleman et al 2008). For northern bobwhites, a combination of ground surface temperature and black globe temperature was a better predictor of the relative probability of use than either of the temperature measurements alone (Olsen et al 2018). Based on these results, we encourage investigators researching the effects of temperature on habitat selection behavior by animals, particularly species in constant contact with the ground, to consider including measurements of ground surface temperature.…”

“…, Olsen et al. ). In ground‐dwelling organisms (e.g., reptiles), ground surface temperature contributes to body temperature in through conduction (Bakken ).…”

“…Black globes provide an estimate of operative temperatures experienced by organisms. Ground surface temperature is another component of the thermal environment that may influence resource use by animals, particularly ground-dwelling organisms (Atienza et al 1996, Cunnington et al 2008, Olsen et al 2018. In ground-dwelling organisms (e.g., reptiles), ground surface temperature contributes to body temperature in through conduction (Bakken 1989).…”