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A Ground-Nesting Galliform's Response to Thermal Heterogeneity: Implications for Ground-Dwelling Birds.

Carroll JM, Davis CA, Elmore RD, Fuhlendorf SD - PLoS ONE (2015)

Bottom Line: We found that thermal space within the study area exhibited differences in Tbb of up to 40°C during peak diurnal heating, resulting in a diverse thermal landscape available to ground-nesting birds.Models of future Tbb associated with 2080 climate change projections indicate that nesting bobwhites will face substantially greater Tbb throughout the landscape for longer durations, placing an even greater importance on thermal choices for nest sites in the future.These results highlight the capacity of landscape features to act as moderators of thermal extremes and demonstrate how thermal complexity at organism-specific scales can dictate habitat selection.

View Article: PubMed Central - PubMed

Affiliation: Department of Natural Resource Ecology and Management, Oklahoma State University, 008C Ag Hall, Stillwater, Oklahoma, United States of America.

ABSTRACT
The habitat selection choices that individuals make in response to thermal environments influence both survival and reproduction. Importantly, the way that organisms behaviorally respond to thermal environments depends on the availability and juxtaposition of sites affording tolerable or preferred microclimates. Although, ground nesting birds are especially susceptible to heat extremes across many reproductive stages (i.e., breeding, nesting, brood rearing), the mechanistic drivers of nest site selection for these species are not well established from a thermal perspective. Our goal was to assess nest site selection relative to the configuration of the thermal landscape by quantifying thermal environments available to a ground-nesting bird species inhabiting a climatically stressful environment. Using northern bobwhite (Colinus virginanus) as a model species, we measured black bulb temperature (Tbb) and vegetation parameters at 87 nests, 87 paired sites and 205 random landscape sites in Western Oklahoma during spring and summer 2013 and 2014. We found that thermal space within the study area exhibited differences in Tbb of up to 40°C during peak diurnal heating, resulting in a diverse thermal landscape available to ground-nesting birds. Within this thermally heterogeneous landscape, nest sites moderated Tbb by more than 12°C compared to random landscape sites. Furthermore, successful nests remained on average 6°C cooler than unsuccessful nests on days experiencing ambient temperatures ≥ 39°C. Models of future Tbb associated with 2080 climate change projections indicate that nesting bobwhites will face substantially greater Tbb throughout the landscape for longer durations, placing an even greater importance on thermal choices for nest sites in the future. These results highlight the capacity of landscape features to act as moderators of thermal extremes and demonstrate how thermal complexity at organism-specific scales can dictate habitat selection.

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Successful nest sites moderated thermal environments more than unsuccessful nests during extreme heat.(A) Mean black bulb temperature (Tbb) (±SE) measured from 09:00–19:00 at successful (n = 54) (dashed line) and unsuccessful (n = 33) northern bobwhite nests (solid line) on days when maximum ambient temperature (Tair) was ≥ 39°C (n = 12) and (B) < 39°C (n = 75) at the Packsaddle WMA, Oklahoma, USA (2013–2014).
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pone.0143676.g004: Successful nest sites moderated thermal environments more than unsuccessful nests during extreme heat.(A) Mean black bulb temperature (Tbb) (±SE) measured from 09:00–19:00 at successful (n = 54) (dashed line) and unsuccessful (n = 33) northern bobwhite nests (solid line) on days when maximum ambient temperature (Tair) was ≥ 39°C (n = 12) and (B) < 39°C (n = 75) at the Packsaddle WMA, Oklahoma, USA (2013–2014).

Mentions: Logistic regression models identified Tbb as the primary single variable predicting nest success (p < 0.05) and the odds of nests being unsuccessful increased with increases in Tbb (i.e., hotter nest sites). Specifically, the candidate model containing nest as a lone variable produced an AIC ranking that was substantially better (DAIC ≥16) than any other models containing single vegetation variables (i.e., visual obstruction, angle of obstruction or vegetation height) (Table 2). Tbb was included in each of the top 8 candidate models and had the strongest effect on nest survival (Table 2) demonstrating that it was a more important variable than the vegetation structure variables that we examined as proxies for potential predation risk. However, significant improvements in AIC rankings were achieved when Tbb and vegetation variables were included together in candidate models (Table 2). Specifically, the top 2 candidate models received similar statistical support (DAIC <2) and included Tbb and angle of obstruction as well as Tbb, angle of obstruction and vegetation height, respectively (Table 2). The four top candidate models accounted for 98% of the Akaike weight (wi) (Table 2) and were used to identify model-averaged coefficients used to solve for odds ratios and 95% confidence intervals. Odds ratios were 1.025 (95% CI, 1.00–1.04), 1.01 (95% CI, 1.00–1.02), 0.86 (95% CI, 0.54–1.38) and 1.0 (95% CI, 0.92–1.09) for Tbb, angle of obstruction, visual obstruction and vegetation height, respectively. Additionally, differences in Tbb between nest fates were temporally explicit with the most pronounced variability occurring during mid-day and afternoon periods on extreme heat days (Tair ≥ 39°C) (Fig 4A). Interestingly, mean Tbb between the 48 successful and 27 unsuccessful nests on days with maximum Tair < 39°C (F1, 805 = 0.034, p = 0.85) (n = 75) (Fig 4B) were similar. However, mean Tbb at the 6 successful nests were on average 6 C°C cooler than at the 6 unsuccessful nests sampled on days experiencing maximum Tair ≥ 39°C (F 1,130 = 6.56, p < 0.05) (n = 12) (Fig 4A).


A Ground-Nesting Galliform's Response to Thermal Heterogeneity: Implications for Ground-Dwelling Birds.

Carroll JM, Davis CA, Elmore RD, Fuhlendorf SD - PLoS ONE (2015)

Successful nest sites moderated thermal environments more than unsuccessful nests during extreme heat.(A) Mean black bulb temperature (Tbb) (±SE) measured from 09:00–19:00 at successful (n = 54) (dashed line) and unsuccessful (n = 33) northern bobwhite nests (solid line) on days when maximum ambient temperature (Tair) was ≥ 39°C (n = 12) and (B) < 39°C (n = 75) at the Packsaddle WMA, Oklahoma, USA (2013–2014).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664423&req=5

pone.0143676.g004: Successful nest sites moderated thermal environments more than unsuccessful nests during extreme heat.(A) Mean black bulb temperature (Tbb) (±SE) measured from 09:00–19:00 at successful (n = 54) (dashed line) and unsuccessful (n = 33) northern bobwhite nests (solid line) on days when maximum ambient temperature (Tair) was ≥ 39°C (n = 12) and (B) < 39°C (n = 75) at the Packsaddle WMA, Oklahoma, USA (2013–2014).
Mentions: Logistic regression models identified Tbb as the primary single variable predicting nest success (p < 0.05) and the odds of nests being unsuccessful increased with increases in Tbb (i.e., hotter nest sites). Specifically, the candidate model containing nest as a lone variable produced an AIC ranking that was substantially better (DAIC ≥16) than any other models containing single vegetation variables (i.e., visual obstruction, angle of obstruction or vegetation height) (Table 2). Tbb was included in each of the top 8 candidate models and had the strongest effect on nest survival (Table 2) demonstrating that it was a more important variable than the vegetation structure variables that we examined as proxies for potential predation risk. However, significant improvements in AIC rankings were achieved when Tbb and vegetation variables were included together in candidate models (Table 2). Specifically, the top 2 candidate models received similar statistical support (DAIC <2) and included Tbb and angle of obstruction as well as Tbb, angle of obstruction and vegetation height, respectively (Table 2). The four top candidate models accounted for 98% of the Akaike weight (wi) (Table 2) and were used to identify model-averaged coefficients used to solve for odds ratios and 95% confidence intervals. Odds ratios were 1.025 (95% CI, 1.00–1.04), 1.01 (95% CI, 1.00–1.02), 0.86 (95% CI, 0.54–1.38) and 1.0 (95% CI, 0.92–1.09) for Tbb, angle of obstruction, visual obstruction and vegetation height, respectively. Additionally, differences in Tbb between nest fates were temporally explicit with the most pronounced variability occurring during mid-day and afternoon periods on extreme heat days (Tair ≥ 39°C) (Fig 4A). Interestingly, mean Tbb between the 48 successful and 27 unsuccessful nests on days with maximum Tair < 39°C (F1, 805 = 0.034, p = 0.85) (n = 75) (Fig 4B) were similar. However, mean Tbb at the 6 successful nests were on average 6 C°C cooler than at the 6 unsuccessful nests sampled on days experiencing maximum Tair ≥ 39°C (F 1,130 = 6.56, p < 0.05) (n = 12) (Fig 4A).

Bottom Line: We found that thermal space within the study area exhibited differences in Tbb of up to 40°C during peak diurnal heating, resulting in a diverse thermal landscape available to ground-nesting birds.Models of future Tbb associated with 2080 climate change projections indicate that nesting bobwhites will face substantially greater Tbb throughout the landscape for longer durations, placing an even greater importance on thermal choices for nest sites in the future.These results highlight the capacity of landscape features to act as moderators of thermal extremes and demonstrate how thermal complexity at organism-specific scales can dictate habitat selection.

View Article: PubMed Central - PubMed

Affiliation: Department of Natural Resource Ecology and Management, Oklahoma State University, 008C Ag Hall, Stillwater, Oklahoma, United States of America.

ABSTRACT
The habitat selection choices that individuals make in response to thermal environments influence both survival and reproduction. Importantly, the way that organisms behaviorally respond to thermal environments depends on the availability and juxtaposition of sites affording tolerable or preferred microclimates. Although, ground nesting birds are especially susceptible to heat extremes across many reproductive stages (i.e., breeding, nesting, brood rearing), the mechanistic drivers of nest site selection for these species are not well established from a thermal perspective. Our goal was to assess nest site selection relative to the configuration of the thermal landscape by quantifying thermal environments available to a ground-nesting bird species inhabiting a climatically stressful environment. Using northern bobwhite (Colinus virginanus) as a model species, we measured black bulb temperature (Tbb) and vegetation parameters at 87 nests, 87 paired sites and 205 random landscape sites in Western Oklahoma during spring and summer 2013 and 2014. We found that thermal space within the study area exhibited differences in Tbb of up to 40°C during peak diurnal heating, resulting in a diverse thermal landscape available to ground-nesting birds. Within this thermally heterogeneous landscape, nest sites moderated Tbb by more than 12°C compared to random landscape sites. Furthermore, successful nests remained on average 6°C cooler than unsuccessful nests on days experiencing ambient temperatures ≥ 39°C. Models of future Tbb associated with 2080 climate change projections indicate that nesting bobwhites will face substantially greater Tbb throughout the landscape for longer durations, placing an even greater importance on thermal choices for nest sites in the future. These results highlight the capacity of landscape features to act as moderators of thermal extremes and demonstrate how thermal complexity at organism-specific scales can dictate habitat selection.

Show MeSH
Related in: MedlinePlus