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Federal Register / Vol. 86, No. 8 / Wednesday, January 13, 2021 / Rules and Regulations other Interior least tern colonies or populations.
Cumulative Effects Our analysis has identified no rangewide threats or stressors with significant effects to all breeding colonies or subpopulations. Monitoring data show some breeding colonies or subpopulation segments may decline or relocate due to localized stressors e.g., predation, disturbance, regional stressors e.g., droughts, floods, or their cumulative effects. Variations in colony locations, size, or subpopulation densities, however, are a characteristic of metapopulation dynamics, and have not been shown to threaten the rangewide status of the Interior least tern over an extended area.
Additionally, the increases documented in the abundance and distribution of the Interior least tern, since it was listed in 1985, do not support a conclusion that any of these stressors cumulatively pose a threat to the Interior least tern.
Future Conditions and Species Viability Species viability, or its ability to survive long term, is related to its ability to withstand catastrophic population and species-level events redundancy, to adapt to changing environmental conditions representation, and to withstand disturbances of varying magnitude and duration resiliency.
The viability of a species is also dependent on the likelihood of new stressors or continued threats now and in the future that act to reduce a species viability.
Redundancy of populations is needed to provide a margin of safety for a species to withstand catastrophic events. Current information and observed trends since the species was listed in 1985 indicate that redundancy of the Interior least tern is currently ensured by the existence of hundreds of breeding colonies in multiple drainages across a wide latitudinal and longitudinal range see Current Distribution and Abundance, above, and within a variety of natural and anthropogenic habitats see Nesting Habitat and Behavior, above.
Representation is the ability of a species to adapt to both near-term and long-term changes in its physical e.g., climate conditions, habitat conditions, and habitat structure and biological e.g., pathogens, competitors, and predators environments. We can gauge representation by examining the breadth of genetic, phenotypic, and ecological diversity found within a species and its ability to disperse and colonize new areas. For the ILT, we evaluated representation across a breadth of
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historical ecological settings, and through preservation of the genetic diversity of the species. The Interior least tern was historically known from, and continues to occur in, two main natural habitat types: Large river sandbars and salt plains. While the salt plains populations were and continue to be historically localized in small portions of the Southern Plains, the sandbar populations occurred across a large latitudinal and longitudinal gradient, encompassing multiple river and stream orders, and a wide variety of climatic conditions. Little evidence of genetic structure has been found within the Interior least tern population Draheim et al. 2010, p. 813, indicating high genetic connectivity between drainage subpopulations. There also appears to be high genetic connectivity between California, Interior, and eastern least terns Draheim et al. 2010, p. 816.
For these reasons, the Interior least tern appears to have adequate genetic and ecological representation to allow for adaptability to environmental changes.
Resiliency allows a species to recover from periodic or occasional disturbance.
Resilience of individual and mated terns is demonstrated by their ability to relocate and re-nest when habitat conditions deteriorate, or when disturbance by humans or predators becomes severe. Interior least tern metapopulation dynamics allow subpopulations and colonies to respond to changing habitat conditions, including their ability to exploit a variety of anthropogenic habitats that were not historically available Lott et al. 2013, p. 3623. This resilience is augmented by the long life span and strong flight abilities of Interior least terns, and by the prospecting behavior exploratory dispersal of young birds across the landscape Boyd and Thompson 1985, p. 405; Lott 2012, p.
12; Shigeta in litt. 2014, entire.
In addition to this review of redundancy, representation, and resiliency, which indicates a high likelihood of future viability for the Interior least tern, the Service worked with multiple partners to develop a habitat-driven, rangewide population model for the tern in order to consider status and population dynamics with and without continued management at local, regional, and rangewide scales Iglay et al. 2012, entire; Lott and Sheppard 2017a, b, entire. The model, known as TernPOP Lott and Sheppard 2017a, b, entire, applied simulation analyses that were designed to explore stakeholder-defined scenarios of potential future habitat change or changes in management. Fifty-five discrete scenarios spanned the
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geographic range of the Interior least tern and covered the topics of 1
sandbar nesting habitat loss, 2 habitat degradation, 3 changes in predator management programs, and 4
deliberate efforts to create mid-channel nesting sandbars for the tern. All 55
scenarios were evaluated relative to a No Action scenario. Thirty replicates of the model were run for 30 years, and population growth or decline rates were calculated for each replicate and then averaged across replicates at the spatial scales of scenario area, subpopulation, drainage population, and the entire listed population of the Interior least tern. Nearly all scenarios of regional management or habitat loss, even some viewed as implausible in the foreseeable future e.g., loss of 50
percent of all sandbars on the Lower Mississippi River, had minimal effects on population growth rates calculated across the 30-year period at the spatial scales of subpopulation, population, and range Lott and Sheppard 2017b, pp. 4261. In most cases, severe habitat degradation in even relatively large areas was insufficient to change the baseline population increases observed during No Action scenarios to population declines, beyond very local areas. Therefore, quantitative evaluation of population model outputs are similar to and support prior qualitative observations that Interior least tern populations are resilient to many potential changes in habitat conditions across their large river network Lott et al. 2013, pp. 36223623; Lott and Sheppard 2017b, pp. 5962.
Based upon the analysis presented above, the Interior least tern cannot be considered to be conservation-reliant, because it has shown to be able to adapt to and exploit substantial habitat changes throughout its range. Although some 10 percent local colonies and peripheral population segments of the Interior least tern may require management for long-term persistence, their success or failure within individual sites is not essential to the continued existence of the Interior least tern. Viability of the Interior least tern is assured by its resilience, representation, and redundancy throughout the remainder of its range.
The Interior least tern will continue to be conserved by habitat management programs in more than 80 percent of its range see Habitat Criteria under Recovery Criteria section, above.
Summary of Comments and Recommendations In our proposed rule published on October 24, 2019 84 FR 56977, we requested that all interested parties
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