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Federal Register / Vol. 86, No. 146 / Tuesday, August 3, 2021 / Rules and Regulations Feeding Individuals of the Sierra Nevada DPS
are opportunistic predators of small mammals such as rodents Perrine et al.
2010, pp. 24, 30, 3233; Cross 2015, p.
72. Leporids such as snowshoe hare Lepus americanus and white-tailed jackrabbit Lepus townsendii are also an important food source for the Sierra Nevada DPS, particularly in winter and early spring Aubry 1983, p. 109; Rich 2014, p. 1; Quinn 2017, pp. 34; Sacks 2017, p. 3.

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Life History Although information regarding Sierra Nevada DPS reproductive biology is limited, it is likely similar in many ways to other North American red fox subspecies Aubry 1997, p. 57. Other subspecies are predominantly monogamous, with a gestation period of 51 to 53 days Perrine et al. 2010, p. 14.
Based on information from both the Sierra Nevada and Southern Cascades populations, Sierra Nevada DPS foxes likely mate in mid-February to early March, with births occurring in April and early May Dunkelberger 2020, p. 1;
Sacks and Quinn 2020, p. 3. This is somewhat later than lowland subspecies, possibly as an adaptation to the later growth of spring vegetation at higher elevations Quinn and Sacks 2020, p. 3. Members of the Sierra Nevada DPS use natural openings in rock piles or crevices in exposed bedrock as denning sites Grinnell et al.
1937, p. 394. Individual foxes from the Southern Cascades population in both Oregon and California have also recently been found to dig earthen dens Dunkelberger 2020, p. 2; Sacks and Quinn 2020, p. 3, suggesting that Sierra Nevada DPS foxes do as well. Dens are used by foxes in the Southern Cascades population and likely in the Sierra Nevada DPS to raise the young from early spring through early fall, and they are often reused from year to year Dunkelberger 2020, pp. 13. A 7-year study of the Sierra Nevada DPS found litter sizes of 2.3 pups on average 9
litters and 21 pups, not counting one purely nonnative litter Quinn and Sacks 2018, p. 38. This is within the range of two to three pups per litter that appear to be typical in the Southern Cascades population Perrine 2005, p.
152. Reproductive output is generally lower in montane foxes than in those living at lower elevations, possibly due to comparative scarcity of food Perrine 2005, pp. 152153; Sacks 2017, p. 2.
Demographics In our proposed listing rule 85 FR
862, p. 866, we estimated the
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population size of the Sierra Nevada DPS at 10 to 50 adults. Based on comments received, we now revise that estimate to approximately 18 to 39
individuals, of which 10 to 31 are north of Yosemite Sacks and Quinn 2020, p.
1, about 5 are in or just east of Yosemite Central Sierra Environmental Resource Center CSERC et al. 2020, pp. 23, California Department of Fish and Wildlife CDFW 2020, p. 4, and 3 have been identified south of Yosemite in the general area of Mono Creek CDFW
2020, p. 3. All detections, including new detections mentioned in comments to the proposed rule, have been within the approximate current range Figure 1. Population density north of Yosemite is estimated at approximately 4 foxes per 100 sq km square kilometers about 1 fox per 10 sq mi square miles Sacks and Quinn 2020, p. 1.
The average lifespan, age-specific mortality rates, sex ratios, and demographic structure of the Sierra Nevada DPS are not known, and are not easily extrapolated from other red fox subspecies because heavy hunting and trapping pressure on those other subspecies likely skew the results Perrine et al. 2010, p. 18. However, three individual Sierra Nevada red fox within the Southern Cascades population in the Lassen area lived at least 5.5 years CDFW 2015, p. 2, and a study of the Sierra Nevada DPS in the Sonora Pass area found the average annual adult survival rate to be about 70
percent, which is relatively high for red foxes Sacks and Quinn 2020, p. 2.
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;
C Disease or predation;

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D The inadequacy of existing regulatory mechanisms; or E Other natural or manmade factors affecting its continued existence.
These factors represent broad categories of natural or human-caused actions or conditions that could have an effect on a species continued existence.
In evaluating these actions and conditions, we look for those that may have a negative effect on individuals of the species, as well as other actions or conditions that may ameliorate any negative effects or may have positive effects.
We use the term threat to refer in general to actions or conditions that are known to or are reasonably likely to negatively affect individuals of a species. The term threat includes actions or conditions that have a direct impact on individuals direct impacts, as well as those that affect individuals through alteration of their habitat or required resources stressors. The term threat may encompasseither together or separatelythe source of the action or condition or the action or condition itself.
However, the mere identification of any threats does not necessarily mean that the species meets the statutory definition of an endangered species or a threatened species. In determining whether a species meets either definition, we must evaluate all identified threats by considering the expected response by the species, and the effects of the threatsin light of those actions and conditions that will ameliorate the threatson an individual, population, and species level. We evaluate each threat and its expected effects on the species, then analyze the cumulative effect of all of the threats on the species as a whole.
We also consider the cumulative effect of the threats in light of those actions and conditions that will have positive effects on the species, such as any existing regulatory mechanisms or conservation efforts. The Secretary determines whether the species meets the definition of an endangered species or a threatened species only after conducting this cumulative analysis and describing the expected effect on the species now and in the foreseeable future.
Analytical Framework The SSA report documents the results of our comprehensive biological status review for the DPS, including an assessment of the potential threats to the species. The SSA report does not represent a decision by the Service on whether the species should be listed as an endangered or threatened species
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