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Federal Register / Vol. 86, No. 8 / Wednesday, January 13, 2021 / Rules and Regulations
distributions, potential effects of climate change on the bird when it is away from its breeding range are unknown. The Interior least tern is well adapted to cope with extreme hydrologic changes, and its habitat and productivity are closely tied with stochastic weather events. For example, while extreme floods may result in annual recruitment loss, such events are also the primary factor in creating, scouring, and maintaining high-quality sandbars where Interior least terns nest Sidle et al. 1992, p. 134. On the other hand, extreme drought events that connect nesting islands to the mainland and result in increased predation of some Interior least tern colonies may be offset by higher abundance of available nesting areas, increased dispersal of reproductive efforts, and higher local recruitment rates of some colonies during low flow periods. Rooftop nesting birds are susceptible to catastrophic recruitment failure due to high summer temperatures see Watterson 2009, pp. 2324; Nupp and Petrick 2010, pp. 57, and colonies on natural habitats may also become negatively affected by increasing summer temperatures. However, Interior least terns are dispersed along a wide latitudinal and longitudinal gradient of climate conditions and are unlikely to experience rangewide catastrophic recruitment failure due to high summer temperatures. Therefore, while Interior least tern colonies may be locally or regionally affected by changes in frequency and duration of extreme flood events and droughts, or high temperatures, the dispersal of the Interior least tern over a wide geographical area encompassing a variety of latitudinal and longitudinal gradients, its long life, and its ability to move long distances indicate the terns resilience to future patterns of predicted effects of climate change Lott et al.
2013, p. 3623.
Habitat Loss and Fragmentation and the Effects of Climate Change Habitat destruction and fragmentation may reduce the likelihood of species surviving the effects of climate change, in part because smaller habitat patches sustain smaller populations Hof et al.
2011, p. 2990. Habitat fragmentation can also impede the dispersal ability of species Hof et al. 2011, pp. 29892990.
While the Interior least tern has possibly been affected by loss of significant reaches of riverine habitat such as the lower Missouri River and lower Red River, it has also increased its longitudinal range by exploiting anthropogenic habitats such as reservoirs in central Texas, Colorado,
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and the Rio Grande, industrial sites in the Wabash River, and coal mines in Texas. Additionally, known population size has also increased by an order of magnitude since the range became fragmented, and genetic studies have demonstrated connectivity via gene flow within Interior least tern populations and between other least tern populations i.e., California least tern and eastern least tern; Whittier et al.
2006, p. 179.
Invasive salt cedar and willow growth, decreases in annual rainfall, and overuse and depletion of aquifers, coupled with increased human water demands, are occurring in the Southern and Northern Plains rivers, possibly to the future detriment of Interior least tern habitat and forage availability in those drainages. However, increases in impervious surfaces e.g., artificial structures or compacted soils associated with human developments may offset the negative effects of climate change in some watersheds, while human demands such as urban or industrial use, and irrigation, could either offset or exacerbate climate change effects in others Caldwell et al. 2012, p. 2854.
Based on current data, the wide longitudinal and latitudinal distribution of the Interior least tern will likely offset any potential localized or regional reduction in habitat quantity or quality, at least in part, by new opportunities in other portions of its range.
Decline of Fish Prey Starvation of California least tern chicks has been reported due to the detrimental effects of El Nino on fish abundance Massey and Fancher 1989, p. 354; Massey et al. 1992, p. 980.
Decreased fish prey availability has been locally linked to reduced Interior least tern egg weights, clutch size, and chick weights, and may have influenced chick survival and fledgling rates Dugger 1997, pp. 9495. Declines in fish prey have been noted on the Missouri River Stucker 2012, p. 21 and in some years on the Mississippi River Dugger 1997, pp. 113114. Fish prey abundance has also been linked to cyclic river conditions e.g., river stage during nesting season; Dugger 1997, p.
26. However, Interior least terns are strong flyers and capable of exploiting a large variety of aquatic habitats and fish species, including exotic species that may invade rivers such as Asian carp.
These characteristics, coupled with the birds long life, its ability to re-nest, and its ability to relocate to more productive areas, enable it to cope with local periodic cycles of low fish prey abundance.

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Other Factors Thompson et al. 1997, pp. 1517
and others have documented the mortality of least tern eggs, chicks, and adults due to a number of additional factors, including flooding of nesting areas during heavy summer rains and high water events, exposure to pesticides and other contaminants of coastal least tern; Jackson and Jackson 1985, p. 58, burial of eggs by sand, hailstorms, heat, cold, sand spurs a common grass in this habitat with prickly burrs that stick to passing animals, fire ants, fireworks, airboats, off-road vehicles ORVs, and human recreationists. Cattle trampling of Interior least tern eggs and chicks has been documented in the Red River Hervey 2001, pp. 78. Nupp 2012, pp.
78 documented mortality of eggs and chicks from heat exposure in rooftop colonies.
Sampling for contaminants in Interior least terns has been concentrated in the Missouri River drainage, where sublethal amounts of arsenic, mercury, chlorinated hydrocarbon, selenium, and polychlorinated biphenyl PCBs have been documented in individuals Fannin and Esmoil 1993, pp. 153157;
Ruelle 1993, pp. 162170; Allen et al.
1998, pp. 358364; however, no incidences of death or decreased fitness of Interior least terns due to contaminants have been reported to date.
ORV impacts have been documented in most drainages where Interior least terns nest Red, Mississippi, Arkansas, Ohio, and Missouri River drainages.
However, ORV access to nesting areas occurs only occasionally because it is usually limited to situations where low flow conditions allow such access.
While other threats i.e., sandstorms, hail storms, heat, cold, sand spurs, fire ants, fireworks, airboats, etc. may increase in frequency and severity in some portions of the Interior least terns range, most are site-specific and sporadic, or otherwise limited in scope.
Interior least tern mortality occurs locally throughout the range due to a variety of natural or manmade factors.
However, the wide distribution of the species, its current high numbers, its long life span, and its ability to relocate and re-nest make the Interior least tern resilient to occasional or periodic local sources of mortality, as well as potential effects of climate change. The increase in range and population size since 1985
indicates that sources of mortality to localized colonies are compensated by these traits of resiliency, as well as by the potential of high recruitment rates in
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