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Federal Register / Vol. 86, No. 103 / Tuesday, June 1, 2021 / Proposed Rules Grasslands are critically endangered globally and an irreplaceable ecoregion in North America, and climate change is an emerging threat to grassland birds Wilsey et al. 2019. In a review of potential effects of ongoing climate change on the Southern Great Plains and on the lesser prairie-chicken, results suggest increases in temperatures throughout the lesser prairie-chicken range and possible increases in average precipitation in the northern part of the range but decreasing precipitation in the southern portion of its range Grisham et al. 2016b, pp. 222227. Weather changes associated with climate change can have direct effects on the lesser prairie-chicken, leading to reduced survival of eggs, chicks, or adults, and indirect effects on lesser prairie-chicken are likely to occur through a variety of means including long-term by mid and late twenty-first century changes in grassland habitat. Other indirect effects may include more secondary causes such as increases in predation pressure or susceptibility to parasites or diseases.
We have little information to describe future grassland conditions as a result of long-term climate changes, although warmer and drier conditions would most likely reduce overall habitat quality for lesser prairie-chicken in much of its range. In general, the vulnerability of lesser prairie-chicken to the effects of climate change depends on the degree to which it is susceptible to, and unable to cope with, adverse environmental changes due to long-term weather trends and more extreme weather events. Based on an analysis of future climate projections the lesser prairie-chicken could have a net loss of more than 35 percent to 50 percent of its range due to unsuitable climate variables Salas et al. 2017, p. 370.
One area of particular vulnerability for the lesser prairie-chicken is the need for specific thermal profiles in the microhabitats they use for nesting and rearing of broods. Warmer air and surface soil temperatures and the related decreased soil moisture near nest sites have been correlated with lower survival and recruitment in the lesser prairie-chicken Bell 2005, pp. 16, 21.
On average, lesser prairie-chicken avoid sites for nesting that are hotter, drier, and more exposed to the wind Patten et al. 2005, p. 1275. Nest survival probability decreased by 10 percent every half-hour when temperature was greater than 93.2 F 34 C and vapor pressure deficit was less than 23
mmHg during the day Grisham et al.
2016c, p. 737. Thermal profiles from nests in some cases exceeded 130 F
54.4 C with humidity below 10

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percent at nests in Texas and New Mexico in 2011, which are beyond the threshold for nest survival Grisham et al. 2013, p. 8. Increased temperatures in the late spring as projected by climate models may lead to egg death or nest abandonment of lesser prairie-chicken Boal et al. 2010, p. 4. Furthermore, if lesser prairie-chicken shift timing of reproduction to later in the year to compensate for lower precipitation, then impacts from higher summer temperatures could be exacerbated. In a study of greater prairie-chickens, heterogeneous grasslands have high thermal variability with a range of measured operative temperatures spanning 41 F 23 C with air temperatures >86 F 30 C Hovick et al. 2014b, pp. 15. In this setting, females selected nest sites that were as much as 14.4 F 8 C cooler than the surrounding landscape.
Although the entire lesser prairiechicken range is likely to experience effects from ongoing climate change, the southern part of the Southern DPS the Shinnery Oak Ecoregion may be particularly vulnerable to warming and drying weather trends, as this portion of the range is already warmer and drier than northern portions and is projected to continue that trend Grisham et al.
2013, entire; Grisham et al. 2016c, p.
742. Research in the Shinnery Oak Ecoregion relating projections in weather parameters in 2050 and 2080 to nest survival found with high certainty that the negative effects on future nest survival estimates will be significant, and the resulting survival rates are too low for population sustainability in the Southern Great Plains in the absence of other offsetting influences Grisham et al. 2013, pp. 67. As late spring and summer daily high temperatures rise, the ability for lesser prairie-chicken to find appropriate nest sites and successfully rear broods is expected to decline. Lower rates of successful reproduction and recruitment lead to further overall declines in population abundance and resiliency to withstand stochastic events such as extreme weather events.
Extreme weather effects such as drought, heat waves, and storms can also directly affect lesser prairie-chicken survival and reproduction and can result in population crashes due to species responses including direct mortality from thermal stress, increased predation due to larger foraging areas, or decreased fitness when food resources are scarce. Like other wildlife species in arid and semiarid grasslands, lesser prairie-chicken on the Southern High Plains have adaptations that increase resilience to extreme environments and
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fluctuating weather patterns; however, environmental conditions expected from climate change may be outside of their adaptive potential, particularly in the timeframe weather changes are expected to occur Fritts et al. 2018, p.
9556. Extreme weather events and periods of drying of soil surface moisture are projected to increase across the lesser prairie-chicken range Easterling et al. 2017, pp. 218222;
Wehner et al. 2017, pp. 237239. In Kansas, extreme drought events in the summers from 1981 through 2014 had a significant impact on lesser prairiechicken abundance recorded at leks;
thus, increases in drought frequency and intensity could have negative consequences for the lesser prairiechicken Ross et al. 2016a, pp. 67.
Even mild increases in drought had significant impacts on the likelihood of population extirpation for lesser prairiechicken De Angelis 2017, p. 15.
Drought is a particularly important factor in considering lesser prairiechicken population changes. The lesser prairie-chicken is considered a boom bust species, meaning that there is a high degree of annual variation in population size due to variation in rates of successful reproduction and recruitment. These variations are largely driven by seasonal precipitation patterns Grisham et al. 2013, pp. 67.
Periods of below-normal precipitation and higher spring/summer temperatures result in less appropriate grassland vegetation cover and fewer food sources, resulting in decreased reproductive output bust periods. Periods with favorable climatic conditions abovenormal precipitation and cooler spring/
summer temperatures will support favorable lesser prairie-chicken habitat conditions and result in high reproductive success boom periods.
The lesser prairie-chicken population failed to rebound for at least 4 years following the 2011 drought Fritts et al.
2018, pp. 95569557. This information indicates either that the extreme environmental conditions during 2011
may have been beyond what the lesser prairie-chicken is adapted to or that the return period following the 20082009
dry period and ensuing low population numbers in 2010 was too short for the population to recover enough to be resilient to the 2011 drought.
The resilience and resistance of species and ecosystems to changing environmental conditions depend on many circumstances Fritts et al. 2018, entire. As climatic conditions shift to more frequent and intense drought cycles, this shift is expected to result in more frequent and extreme bust years for the lesser prairie-chicken and fewer
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