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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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Thermal environments at proximate (within 2 m) paired control sites greatly exceed those at nest sites.Mean black bulb temperature (Tbb) (±SE) measured from 09:00–19:00 h at northern bobwhite nests (light gray) (n = 87) and paired control sites (dark gray) (n = 87) at the Packsaddle WMA, Oklahoma, USA (2013–2014).
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pone.0143676.g003: Thermal environments at proximate (within 2 m) paired control sites greatly exceed those at nest sites.Mean black bulb temperature (Tbb) (±SE) measured from 09:00–19:00 h at northern bobwhite nests (light gray) (n = 87) and paired control sites (dark gray) (n = 87) at the Packsaddle WMA, Oklahoma, USA (2013–2014).

Mentions: Nest sites acted as buffers against thermal conditions occurring on the surrounding landscape by remaining warmer at Tair < 28°C; yet cooler than landscape sites at Tair > 28°C (Fig 1B). Furthermore, we observed that the thermal buffering provided by nest sites substantially decoupled nests from surrounding conditions by reducing the amplification of Tbb relative to that of landscape (Fig 2). Specifically, standardized mean differences (±SE) between Tbb and Tair (i.e., Tbb—Tair) were more than twice as much at landscape sites (5.4°C greater) during diurnal periods (09:00–19:00) (Fig 2). Under the assumption that nest and landscape Tbb remained relatively consistent within 15 minute sampling periods, this difference of 5.4°C would result in an additional 1,620 degree-minutes of additional heat loads during the hottest parts of the day (11:00–16:00 h) (i.e., 5.4°C x 5 h x 60 min/h) [54]. Although nest sites moderated microclimates more than the surrounding landscape, we also observed the potential for extreme Tbb at sites selected for nesting. As expected, we observed temporal differences between nest Tbb and paired control site Tbb throughout the day, however, differences were substantial (Fig 3). Specifically, discrepancies in Tbb increased incrementally and peaked during the afternoon concomitant to daily Tair and Srad maximums. Not only was average nest Tbb cooler than at paired sites or landscape sites, maximum Tbb recorded at nests was more than 10°C less (61.9°C) than at microsites (72.1°C) or landscape points (72.1°C).


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)

Thermal environments at proximate (within 2 m) paired control sites greatly exceed those at nest sites.Mean black bulb temperature (Tbb) (±SE) measured from 09:00–19:00 h at northern bobwhite nests (light gray) (n = 87) and paired control sites (dark gray) (n = 87) 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.g003: Thermal environments at proximate (within 2 m) paired control sites greatly exceed those at nest sites.Mean black bulb temperature (Tbb) (±SE) measured from 09:00–19:00 h at northern bobwhite nests (light gray) (n = 87) and paired control sites (dark gray) (n = 87) at the Packsaddle WMA, Oklahoma, USA (2013–2014).
Mentions: Nest sites acted as buffers against thermal conditions occurring on the surrounding landscape by remaining warmer at Tair < 28°C; yet cooler than landscape sites at Tair > 28°C (Fig 1B). Furthermore, we observed that the thermal buffering provided by nest sites substantially decoupled nests from surrounding conditions by reducing the amplification of Tbb relative to that of landscape (Fig 2). Specifically, standardized mean differences (±SE) between Tbb and Tair (i.e., Tbb—Tair) were more than twice as much at landscape sites (5.4°C greater) during diurnal periods (09:00–19:00) (Fig 2). Under the assumption that nest and landscape Tbb remained relatively consistent within 15 minute sampling periods, this difference of 5.4°C would result in an additional 1,620 degree-minutes of additional heat loads during the hottest parts of the day (11:00–16:00 h) (i.e., 5.4°C x 5 h x 60 min/h) [54]. Although nest sites moderated microclimates more than the surrounding landscape, we also observed the potential for extreme Tbb at sites selected for nesting. As expected, we observed temporal differences between nest Tbb and paired control site Tbb throughout the day, however, differences were substantial (Fig 3). Specifically, discrepancies in Tbb increased incrementally and peaked during the afternoon concomitant to daily Tair and Srad maximums. Not only was average nest Tbb cooler than at paired sites or landscape sites, maximum Tbb recorded at nests was more than 10°C less (61.9°C) than at microsites (72.1°C) or landscape points (72.1°C).

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