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Federal Register / Vol. 86, No. 243 / Wednesday, December 22, 2021 / Proposed Rules
extinction now i.e., endangered. In undertaking this analysis for cactus ferruginous pygmy-owl, we choose to address the status question firstwe consider information pertaining to the geographic distribution of both the species and the threats that the species faces to identify any portions of the range where the species is endangered.
The statutory difference between an endangered species and a threatened species is the timeframe in which the species becomes in danger of extinction;
an endangered species is in danger of extinction now while a threatened species is not in danger of extinction now but is likely to become so in the foreseeable future. Thus, we reviewed the best scientific and commercial data available regarding the time horizon for the threats that are driving the cactus ferruginous pygmy-owl to warrant listing as a threatened species throughout all of its range. We considered whether the threats are geographically concentrated in any portion of the species range in a way that would accelerate the time horizon for the species exposure or response to the threats. We examined the following threats: Climate change and climate condition Factor E and habitat loss and fragmentation Factor A, including cumulative effects.
We found a concentration of threats, i.e., the impacts of climate change, urbanization, and invasive species, in the Sonoran Desert Ecoregion, which extends from Arizona south into Sonora, Mexico. Climate change impacts to the pygmy-owl in the Sonoran Desert Ecoregion are likely to include loss of vegetation cover, reduced prey availability, increased predation, reduced nest site availability, and vegetation community change. For example, models predict that the distribution of suitable habitat for saguaros, the primary pygmy-owl nesting substrate within the Sonoran Desert Ecoregion, will substantially decrease over the next 50 years under a moderate climate change scenario Weiss and Overpeck 2005, p. 2074;
Thomas et al. 2012, p. 43.
Climate models project that, by the end of the 21st century, the Sonoran Desert will experience an increase in drought conditions with a transition to a drier and more arid climate Seager et al. 2007, p. 9; Cook et al. 2015, p. 6;
Pascale et al. 2017, p. 806; Williams et al. 2020, p. 317. Given that this portion of the pygmy-owls overall range is already characterized by arid and hot conditions and is in the midst of an extended drought, the effects from climate change represent a higher concentration of effects than in other
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portions of the pygmy-owls range, which generally are characterized by higher precipitation and lower temperatures resulting in a baseline of higher greenness and vegetation health.
In general, annual precipitation in the Sonoran Desert is positively correlated to pygmy-owl productivity Flesch et al.
2015, p. 26. Timing and quantity of precipitation affects lizard and rodent abundance in ways that suggest rainfall is an important driver of prey population and community dynamics.
In general, cool-season rainfall is positively correlated with rodent populations and warm-season rainfall is positively correlated with lizard populations. Projected increases in variability and decreases in quantity of precipitation will likely lead to a decrease in prey abundance for the pygmy-owl Jones 1981, p. 111; Flesch 2008, p. 5; Flesch et al. 2015, p. 26.
Urban expansion and human population growth trends are expected to continue in the Sonoran Desert Ecoregion. The Maricopa-Pima-Pinal County areas of Arizona are expected to see the population grow by as much as 132 percent between 2005 and 2050, creating rural-urban edge effects across thousands of acres of pygmy-owl habitat AECOM 2011, p. 13.
The population along the U.S.-Mexico border region from Texas to California is expected to double by 2025 HHS 2017, p. 1. In Arizona, the border counties are projected to increase by 60 percent to 2.5 million by 2050 OEO 2021, unpaginated. In Sonora the population is projected to reach 3.5 million by 2030
CONAPO 2014, p. 25. Development is focused along the border and this area of northern Mexico has faster population growth than other Mexican states Pineiro 2001, pp. 12. This development focuses potential barriers or impediments to pygmy-owl movements in a region that is important for demographic support immigration events and gene flow of pygmy-owl population groups, including movements such as dispersal. If urban expansion and development continues as expected, it will encompass a substantial portion of the current distribution of the pygmy-owl in the Sonoran Desert Ecoregion.
The invasion of nonnative vegetation, particularly nonnative grasses, has altered the natural fire regime over the Sonoran Desert Ecoregion portion of the pygmy-owls range. Buffelgrass is prevalent and increasing throughout much of this portion of the pygmy-owls range, leading to increased fire frequency in a system that is not adapted to fire Schmid and Rogers 1988, p. 442; DAntonio and Vitousek
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1992, p. 73; Burquez and Quintana 1994, p. 23; Halverson and Guertin 2003, p. 13; Van Devender and Dimmit 2006, p. 5. While a single fire in an area may or may not produce long-term reductions in plant cover or biomass, repeated wildfires in a given area are capable of ecosystem type-conversion from native desertscrub to nonnative annual grassland. These repeated fires may render the area unsuitable for pygmy-owls and other native wildlife due to the loss of trees and columnar cacti, and reduced diversity of cover and prey species Brooks and Esque 2002, p. 336.
Despite the current concentration of threats and their increasing effects to pygmy-owls and pygmy-owl habitat, the Sonoran Desert Ecoregion currently supports an abundance of pygmy-owls in the high hundreds and a moderate amount of intact, suitable vegetation.
Consequently, these factors are currently maintaining an overall moderate level of resiliency in this portion of the range. Additionally, there is currently habitat connectivity with evidence of pygmy-owl movement among population groups, providing redundancy throughout the Sonoran Desert Ecoregion. Representation is also currently being maintained through pygmy-owl occupancy of a variety of vegetation types throughout the Sonoran Desert Ecoregion with gene flow among these population groups. However, under all three future scenarios, this portion of the range is expected to become less resilient due to continued habitat fragmentation and the effects of climate change on habitat conditions, resulting in a reduction of pygmy-owl abundance and occupancy. These deteriorating conditions are also anticipated to result in declines in redundancy and representation through the loss of population groups within the Ecoregion.
Although some threats to the cactus ferruginous pygmy-owl are concentrated in the Sonoran Desert Ecoregion, the best scientific and commercial data available does not indicate that the concentration of threats, or the species responses to the concentration of threats, are likely to accelerate the time horizon in which the species becomes in danger of extinction in that portion of its range. As a result, the cactus ferruginous pygmy-owl is not in danger of extinction now in the Sonoran Desert Ecoregion. However, we do find that the species is likely to become in danger of extinction within the foreseeable future throughout all of its range. This finding is consistent with the courts holdings in Desert Survivors v. Department of the Interior, No. 16cv01165JCS, 2018

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