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.

No abstract

There has been recent concern regarding the effects of range management practices on biodiversity. Our objective was to determine the long-term (~30 years) effects of chaining, and chaining followed by root plowing, on vegetation diversity in an ephemeral drainage system. Plant species richness and diversity were estimated in 2 chained (ca. 1950) areas, 2 chained (ca. 1950) and root-plowed (ca. 1960) areas, and 2 untreated areas during April 1993. Beta diversity within treatments was estimated with mean dissimilarity (l-mean similarity). Mean similarity was quantified with Jaccard's index. Spatial gradient analysis in which pairwise similarities were regressed against the distance between each pair of samples within a site was used to describe similarity within a site. Species richness and diversity were similar among treatments for both herbaceous and woody species. Similarity (Jaccard's index) among transects within a site increased with increasing degree of disturbance. Chained and root plowed sites had lower beta diversity than chained or untreated sites. Similarity in the chained and root plowed sites varied randomly, not spatially, while the control (untreated) and chained sites had negative spatial gradients, indicating spatial heterogeneity within these sites. Although root plowing did not reduce species richness and diversity as reported on upland sites in previous studies, beta diversity and habitat heterogeneity were lower on chained and root plowed sites than on chained or untreated sites.

Animals use physiological and behavioral adaptations to maintain constant body temperatures when environmental temperatures are outside of their thermoneutral zone. We define the temperature suitability bounds as the range of temperatures above and below which animals avoid locations because of unfavorable thermal conditions. Temperatures outside the temperature suitability bounds may trigger behavioral responses such as movement to cooler locations. We tested the hypothesis that temperature during late April to August influences resource selection using chestnut‐bellied scaled quail (Callipepla squamata castanogastris) as our study species. We estimated temperature suitability bounds for scaled quail and tested the prediction that ground surface temperature is a better predictor of habitat space use than black globe temperature. We compared models containing ground surface temperature and woody vegetation structure variables to test the hypothesis that including woody vegetation variables improves prediction of relative probability of use. We trapped scaled quail at five different locations in southern Texas. We located quail fitted with necklace‐style transmitters three times/week during 2013–2014. We measured ground surface and black globe temperatures at locations used by scaled quail and at random locations. We estimated percent canopy cover of cacti, subshrubs, and woody plants using 20 × 50 cm Daubenmire frames at each used and random location. We also estimated height and vertical obstruction of woody vegetation. Temperature suitability bounds of scaled were 24–43°C for the ground surface and 23–39°C for black globes. Ground surface temperature was a better predictor of relative probability of use than black globe temperature. Ground surface temperature during the warmest time of day (early afternoon, 13:30–17:29) decreased with increasing vertical obstruction after accounting for the influence of other structural variables. The best model for predicting relative probability of use by scaled quail during the warmest time of day included ground surface temperature and vertical obstruction. Use of microsites where vegetation structure is conducive to cooler temperatures is an important driver of resource selection by scaled quail during the warmest time of day in southern Texas, but availability of thermal refugia appears to be limited.

No abstract