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Federal Register / Vol. 86, No. 103 / Tuesday, June 1, 2021 / Proposed Rules
survey efforts should not be taken as precise estimates of the annual lesser prairie-chicken abundance, as indicated by the large confidence intervals. Thus, we caution the reader not to draw conclusions based upon annual fluctuations. Instead, we consider the best use of this data is for long-term trend analysis. Thus, in the SSA Report and this proposed rule, we report the population estimate for the current condition as the average of the past 5
years of surveys.

The results of the study using lek data abundance of males indicate that lesser prairie-chicken range-wide abundance based on a minimum estimated number of male lesser prairiechicken at leks peaked from 19651970
at a mean estimate of about 175,000
males Figure 1. The estimated mean population maintained levels of greater than 100,000 males until 1989, after which they steadily declined to a low of 25,000 males in 1997 Garton et al.
2016, p. 68. The mean population
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estimates following 1997 peaked again at about 92,000 males in 2006, but subsequently declined to 34,440 males in 2012 Figure 1.
The aerial survey results from 2012
through 2020 Figure 2 estimated the lesser prairie-chicken population abundance, averaged over the most recent 5 years of surveys 20152020, no surveys in 2019, at 27,384 90%
confidence interval: 15,690, 59,981
Nasman et al. 2020, p. 21; Table 3.3.

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Figure 1. Estimated range-wide minimum number of Lesser Prairie-Chicken males attending leks 1964-2016 90% confidence interval. Based on population reconstruction using 2016 aerial survey as the initial population size reproduced from Hagen et al. 2017.

The preferred habitat of the lesser prairie-chicken is mixed-grass prairies and shrublands, with the exception of the Short-Grass/CRP Ecoregion where shrubs play a lesser role. Lesser prairiechickens appear to select areas having a shrub component dominated by sand sagebrush or sand shinnery oak when those areas are available Donaldson 1969, pp. 56, 62; Taylor and Guthery 1980a, p. 6; Giesen 1998, pp. 34. In the southern and central portions of the lesser prairie-chicken range, small shrubs, such as sand shinnery oak, have been reported to be important for summer shade Copelin 1963, p. 37;
Donaldson 1969, pp. 4445, 62, winter protection, and as supplemental foods Johnsgard 1979, p. 112, while in the Short-Grass/CRP Ecoregion, stands of grass that provide adequate vegetative structure likely serve the same roles.
The absence of anthropogenic features as well as other vertical structures is important, as lesser prairie-chickens
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Figure 2. Annual estimates of total range-wide population size of lesser prairie-chicken from 2012-2020. Bars represent the bootstrapped 90%
confidence intervals. Graph generated from Nasman et al. 2020, Table 12, p. 21. There were no surveys in 2019.

tend to avoid using areas with trees, vertical structures, and other disturbances in areas with otherwise adequate habitat conditions Braun et al.
2002, pp. 1113; Pruett et al. 2009, pp.
1256, 1258; Hovick et al. 2014a, p. 1685;
Boggie et al. 2017, entire; Lautenbach 2017, pp. 104142; Plumb et al. 2019, entire.
At the population scale, the most important requirement for the lesser prairie-chicken is having large, intact, ecologically diverse grasslands to complete their life history and maintain healthy populations Fuhlendorf et al.
2017b, entire. Historically, these ecologically diverse grasslands and shrublands were maintained by the occurrence of wildfires keeping woody vegetation restricted to drainages and rocky outcroppings and by grazing by bison and other large ungulates. The lesser prairie-chicken is a species that is area-sensitive; that is, it requires large, intact grasslands for functional self-

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sustaining populations Giesen 1998, pp. 34; Bidwell et al. 2002, pp. 13;
Hagen et al. 2004, pp. 71, 7677; Haukos and Zavaleta 2016, p. 107.
The lesser prairie-chicken now occurs within four ecoregions Figure 3; these ecoregions were originally delineated in 2012 as part of the aerial survey designed to monitor long-trends in lesser prairie-chicken populations. Each ecoregion is associated with unique environmental conditions based on habitat and climatic variables and some genetic differentiation Boal and Haukos 2016, p. 5; Oyler-McCance et al. 2016, p. 653. These four ecoregions are the Short-Grass Prairie/CRP Mosaic Ecoregion in Kansas; the Sand Sagebrush Prairie Ecoregion in Colorado, Kansas, and Oklahoma; the Mixed-Grass Prairie Ecoregion in Kansas, Texas, and Oklahoma; and the Sand Shinnery Oak Prairie Ecoregion of New Mexico and Texas.

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