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Federal Register / Vol. 86, No. 243 / Wednesday, December 22, 2021 / Proposed Rules individuals to replace members of breeding pairs that have been lost and to support persistent population groups of nesting pygmy-owls through dispersal. However, the necessary reproductive rate needed for a selfsustaining population is unknown.
Additionally, key demographic parameters of pygmy-owl populations e.g., survival, life expectancy, lifespan, productivity, etc. are unknown throughout most of the geographic range. Due to the lack of information on demographic parameters of reproduction, recruitment, and survival, we broadly considered evidence of reproduction to include any evidence of reproduction e.g., active nests, presence of eggs or nestlings, fledglings, etc., as well as persistence of occupied territories and population groups in an area over a sufficient amount of time to indicate evidence of reproduction.
Thus, evidence of reproduction on a consistent basis over time likely indicates a sufficiently resilient population.
Habitat intactness: Adequately resilient pygmy-owl populations need intact habitat that is large enough to support year-round occupancy, as well as connectivity between habitat patches to enable dispersal. Pygmy-owls are patchily distributed across much of their geographic range. These pygmyowl population groups are dependent on interchange of individuals in order to maintain adequate numbers and genetic diversity on the landscape. Habitat connectivity is crucial to maintaining pathways for the interchange of individuals among pygmy-owl population groups.
Prey availability: Adequate prey availability is a key component for maintaining resiliency in pygmy-owl populations. Year-round prey availability is essential throughout the range of the pygmy-owl, with portions of the geographic range characterized by seasonal variability in available prey resources. The abundance of many of these prey species is influenced by annual and seasonal precipitation through increases and decreases in vegetation cover and diversity, which also influences insect abundance and availability. Sufficiently resilient pygmy-owl populations require adequate precipitation to support yearround prey availability. This includes appropriately timed precipitation to support seasonally available prey such as lizard, insects, and small mammals.
Vegetation cover: Sufficiently resilient pygmy-owl populations require adequate vegetation to provide cover for predator avoidance, thermoregulation, hunting, and nest cavities. Of primary
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importance for cover is the presence of woody vegetation canopy. Maintenance of the health and vigor of this woody cover is a key component to maintaining resiliency of pygmy-owl populations.
Summary of Current Condition of the Subspecies Currently, the cactus ferruginous pygmy-owl occurs from southern Arizona, south to Michoacan in the western portion of its range, and from southern Texas to Tamaulipas and Nuevo Leon in the eastern portion of its range. For our analysis, we divided the pygmy-owls overall range into five analysis units: Arizona, northern Sonora, western Mexico, Texas, and northeastern Mexico see Figure 1, below. The primary factors currently affecting the condition of cactus ferruginous pygmy-owl populations include climate conditions, and habitat fragmentation and loss.
Resiliency The Arizona analysis unit currently has the lowest pygmy-owl abundance of all analysis units, which is estimated to be in the low hundreds. Habitat fragmentation and loss from urbanization and increases in invasive species such as buffelgrass, have reduced the availability and connectivity of habitat in this analysis unit. Additionally, climate conditions have reduced prey availability and vegetative cover through increased temperatures and drought. These factors result in a reduced capacity for this analysis unit to withstand stochastic events and result in a low resiliency currently.
The northern Sonora analysis unit has an estimated pygmy-owl abundance in the high hundreds. However, this analysis unit is affected by habitat fragmentation from urbanization, agricultural development, and associated infrastructure. These stressors increase water use and, in conjunction with climate conditions, result in a reduction in the quality and availability of pygmy-owl habitat. Due to moderate owl abundance and some decrease in habitat availability and connectivity, the northern Sonora analysis unit has a moderate level of population resiliency.
The western Mexico analysis unit is estimated to have tens of thousands of pygmy-owls. This analysis unit has some habitat fragmentation from urbanization, agricultural development, and deforestation of the tropical deciduous forests. Overall, the western Mexico analysis unit has high population resiliency due to high abundance of pygmy-owls and healthy
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vegetation cover, likely as a result of high levels of precipitation in the region.
The Texas analysis unit has an estimated pygmy-owl abundance in the high hundreds. Land ownership within this analysis unit has resulted in habitat fragmentation and, due to agricultural development and wood harvesting within the Rio Grande Valley, this analysis unit is somewhat genetically isolated from the rest of the geographic range of the subspecies. Due to moderate pygmy-owl abundance, fragmentation of habitat, and some genetic isolation, the Texas analysis unit has a moderate level of population resiliency.
The northeast Mexico analysis unit is estimated to have tens of thousands of pygmy-owls. However, this unit has high levels of habitat fragmentation due to urbanization and agricultural development. Overall, the northeast Mexico analysis unit has a moderate level of population resiliency with some capacity to withstand stochastic events.
Rangewide, current condition of the pygmy-owl populations indicate that three analysis units are maintaining a moderate level of population resiliency, one analysis has low resiliency, and one analysis unit has high resiliency.
Representation Resiliency, and the factors that drive resiliency, also contribute to the pygmyowls representation on the landscape.
Pygmy-owls occupy a diversity of habitat types throughout the geographic range of the subspecies and maintain substantial genetic diversity. The subspecies adaptive potential representation is currently high due to genetic and ecological variability across the range. There is substantial genetic diversity across the range Proudfoot et al. 2006a, entire; 2006b, entire due to isolation-by-distance and geographic barriers. Additionally, across the range, the pygmy-owl occupies a diverse range of ecological settings as a result of geographic gradients of vegetation, climate, elevation, topography, and other landscape elements. Such ecological diversity could help the pygmy-owl adapt to and survive future environmental changes, such as warming temperatures or decreased precipitation from climate change.
Redundancy We assessed the number and distribution of populations across the pygmy-owls geographic range as a measure of its redundancy. While the numbers and densities of pygmy-owls are lower in some analysis units, these portions of the range still contribute in
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