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Federal Register / Vol. 86, No. 185 / Tuesday, September 28, 2021 / Proposed Rules
I. Proposed Listing Determination Background The Penasco least chipmunk Neotamias minimus atristriatus is currently recognized as one of 17
subspecies of least chipmunk Neotamias =Tamias minimus Wilson and Reeder 2005, p. 815. Least chipmunks are smaller than most other chipmunk species and belong to the family Sciuridae. The Penasco least chipmunk is known from the Sacramento Mountains and White Mountains in Lincoln and Otero Counties in southern New Mexico.
Penasco least chipmunks are grayishbrown mixed with cinnamon-buff on the rump and thighs Sullivan 1993, p.
1, with a blackish head with white and cinnamon, and a whitish patch behind each ear. The sides of their bodies are light brown, and underparts are whitish with buff; their feet are light pinkcinnamon; the tail is blackish or brown with pinkish-cinnamon; and dark stripes on the back and head are blackish to blackish-brown, edged with tawny along the spine, and bordered with white on the face and sides Sullivan 1993, pp. 12. The Penasco least chipmunk has pale yellowish orange hindfeet, a light beige, yellowish, or orange belly, and dark underfur Frey 2010, p. 11. A full species description and description of its habitat can be found in chapter 2 of the SSA report.
The Penasco least chipmunk was first described as a new species, Eutamias atristriatus, in 1913 based on 10
specimens collected from ponderosa pine forest in the Sacramento Mountains in 1902 Bailey 1913, entire.
This taxonomy has been revised multiple times as the taxonomy of chipmunks and least chipmunks changed, including use of the synonyms Eutamias and Tamias for Neotamias.
Howell 1929, entire designated the taxon a subspecies of least chipmunk, Tamias minimus atristriatus. Conley 1970, entire purported that the South Sacramento = Sacramento Mountains population was the only population of least chipmunks in New Mexico worthy of nomenclatural distinction based on morphological distinctiveness.
However, Sullivan and Peterson 1988, p. 21 recommended the retention of N.
m. atristriatus as a subspecies that included both the New Mexico White Mountains and Sacramento Mountains, based on more in-depth morphological and genetic analyses. Verts and Carraway 2001, entire and Wilson and Reeder 2005, p. 815 continue to support N. m. atristriatus as a recognized subspecies of N. minimus.
Least chipmunks are currently
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recognized as belonging to the genus Neotamias Patterson and Norris 2016, p. 248. There is currently no disagreement regarding the distinctiveness of the subspecies from other subspecies of least chipmunk, nor from the sympatric gray-footed chipmunk N. canipes. The Penasco least chipmunk is thus currently recognized as a valid subspecies, N.
minimus atristriatus Wilson and Reeder 2005 p. 815.
Habitat occupied by Penasco least chipmunk varies by population between the Sacramento and White Mountains.
In the Sacramento Mountains, Penasco least chipmunk habitat use has generally been mature, open ponderosa pine forest savanna and adjacent valley meadows Frey and Hays 2017, p. 1.
Specimens of the Penasco least chipmunk from the Sacramento Mountains were originally described from the yellow pine zone = ponderosa pine Bailey 1913, p. 130 and within the transition zone from the juncture of yellow pines and junipers up to the edge of spruce-fir forest Bailey 1931, p.
91. However, the Penasco least chipmunk has not been detected in the Sacramento Mountains since 1966, so our understanding of habitat use and distribution in that area is limited to historical records and reports.
In the White Mountains, the Penasco least chipmunk is associated with the high-elevation subalpine Thurbers fescue meadow biotic community Frey and Hays 2017, p. 34. This habitat is distinctly different from the lower elevation, montane meadow grassland communities within mixed conifer and ponderosa pine forest zones Dyer and Moffett 1999, entire; Dick-Peddie 1993, pp. 101 104, as would be found in the Sacramento Mountains. In the White Mountains, our understanding of subspecies occurrence and habitat use is informed by capture information as recent as 2018, but is still limited by few observational records of the subspecies.
Least chipmunks forage mainly on the ground or in shrubs Hoffmeister 1986, p. 15. They eat a variety of seeds of shrubs, forbs, and some conifers, and other plant parts and fungi as their main food sources; they also feed on animal foods such as arthropods, carrion, and bird eggs Bailey 1931, p. 91; Vaughn 1974, pp. 770772; Reid 2006, p. 212.
The least chipmunk does not develop additional fat deposits in the fall, but relies primarily on brief periods of activity to consume cached food for survival over the winter Verts and Carraway 2001, p. 7, hibernating in this case, overwintering with periods of both torpor and activity in special underground chambers Reid 2006, p.

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212. Penasco least chipmunks in the White Mountains likely forage primarily on the seeds and flowers of forbs, particularly species of Asteraceae Frey and Hays 2017, p. 34. Bailey 1931, p.
91 observed the subspecies foraging on sunflower Helianthus spp. seeds along fencelines and on wheat Triticum sp.
and oats Avena sativa at the edges of agricultural fields in the Sacramento Mountains. The diet also includes flowers and fruits of gooseberry Ribes spp. and wild strawberry Fragaria spp., pinyon Pinus edulis nuts, Gambel oak Quercus gambelii acorns, insects, and other items Sullivan 1993, p. 3. Like other least chipmunks, the Penasco least chipmunk likely has relatively low water requirements, which may allow it to exploit the drier conditions of open subalpine meadows Frey and Hays 2017, p. 34.
Least chipmunk breeding takes place soon after emergence from the hibernation chambers Reid 2006, p.
212. In spring, females typically produce one litter of four to five pups Skryja 1974, p. 223, but the size of the litter can range from three to eight, with young being born in May or June Reid 2006, p. 212. For Penasco least chipmunks, young are thought to be born in midto late-summer, as halfgrown juveniles were observed historically in early September in the Sacramento Mountains Bailey 1931, p.
91. The average lifespan of least chipmunks overall is 0.7 years Erlien and Tester 1984, p. 2, but individuals have been known to live up to 6 years Reid 2006, p. 212.
Regulatory and Analytical Framework Regulatory Framework Section 4 of the Act 16 U.S.C. 1533
and its implementing regulations 50
CFR part 424 set forth the procedures for determining whether a species is an endangered species or a threatened species. The Act defines an endangered species as a species that is in danger of extinction throughout all or a significant portion of its range, and a threatened species as a species that is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range. The Act requires that we determine whether any species is an endangered species or a threatened species because of any of the following factors:
A The present or threatened destruction, modification, or curtailment of its habitat or range;
B Overutilization for commercial, recreational, scientific, or educational purposes;

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