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Federal Register / Vol. 86, No. 161 / Tuesday, August 24, 2021 / Rules and Regulations mi to the north and south, and 113 km 70 mi east to west, between 122 to 124 west longitude and 40 58 to 43
30 north latitude in Douglas, Jackson, and Josephine Counties in southern Oregon, and Siskiyou and Trinity Counties in northern California Thorp 1999, p. 3; Thorp 2005, p. 1;
International Union for Conservation of Nature 2009, p. 1.
Franklins bumble bee was first observed in 1917, and first described in 1921, and limited occurrence and observation data exist for Franklins bumble bee prior to 1998. The species has been found on many privately owned sites as well as municipal, State, and Federal land. Historical observations and occurrence data for Franklins bumble bee prior to 1998
include opportunistic observations, student collections, and museum specimens, as well as the collections and notes of interested parties, natural resource managers, and university staff Xerces Society and Thorp 2010, pp. 34
40. A more intensive and targeted search effort for the species began in 1998, in areas thought to have the highest likelihood of Franklins bumble bee presence. There was initial success at finding a higher abundance of the species than ever previously reported;
in one year 1998, 98 Franklins bumble bees were observed mostly from two sites. However, in subsequent years, searchers found fewer and fewer Franklins bumble bees, and none have been found since the last sighting of a single individual in Oregon in 2006.
The variations in timing, scope, intensity, and methodology of search efforts including those since 1998 and the lack of observations since 2006
prevent the identification of any population trends. Many of the occurrence records provide only point data for an occurrence, with no details on the size of the area searched or whether or not the record reflected a comprehensive search of an area. Many records also lack details on the level of survey effort per location number of searchers, hours of search effort per day, number of days per search effort.
The lack of systematic surveys across the historical range of the species over time prevents us from using occurrence records to extrapolate reasonable estimates of species abundance or distribution or from concluding that the species is extinct. Even though none have been seen since 2006, Franklins bumble bee populations could potentially persist undetected. The areas chosen for survey were selected due to a combination of abundance of floral resources throughout the colony cycle, relatively recent historical occurrence of
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the species, and accessibility to surveyors. However, the surveyed area represents a relatively small percentage of the historical range of the Franklins bumble bee; therefore, it is possible the species may persist in other areas of the range. There are numerous instances of species rediscovered after many years, even decades, of having been believed extinct e.g., Scheffers et al. 2011, entire. As one example of such a case, the Fenders blue butterfly Icaricia icarioides fenderi of Oregon was believed extinct after the last recorded observation in 1937, until it was rediscovered in 1989, 52 years later Hammond and Wilson 1992, p. 175;
Hammond and Wilson 1993, p. 2.
Recent approaches to evaluating extinction likelihood place increased emphasis on the extensiveness and adequacy of survey effort Keith et al.
2017, p. 321; Thompson et al. 2017, p.
328, and caution against declaring a species as extinct in the face of uncertainty Akcakaya et al. 2017, p.
340.
The specific life-history characteristics and behavior of this rare species have not been studied; much of the information presented in the SSA
report Service 2018a, entire is inferred from information on Bombus in general and some closely related species western bumble bee B. occidentalis, rusty patched bumble bee B. affinis, and yellow-faced bumble bee B.
vosnesenskii, among others. The report also relied heavily on information from species experts Service 2018a, entire.
Franklins bumble bee is a primitively eusocial bumble bee, meaning they are highly social and adults have flexible roles in their social order. They live in colonies made up of a queen and her male and worker offspring, and adult females can switch from worker to queen roles. Like other eusocial Bombus species, Franklins bumble bee typically nests underground in abandoned rodent burrows or other cavities that offer resting and sheltering places, food storage, nesting, and room for the colony to grow Plath 1927, pp. 122
128; Hobbs 1968, p. 157; Thorp et al.
1983, p. 1; Thorp 1999, p. 5. The species may also occasionally nest on the ground Thorp et al. 1983, p. 1 or in rock piles Plowright and Stephen 1980, p. 475. It has even been found nesting in a residential garage in the city limits of Medford, Oregon Thorp 2017, pers. comm..
Colonies of Franklins bumble bee have an annual cycle, initiated each spring when solitary queens emerge from hibernation and seek suitable nest sites Thorp 2017, pers. comm..
Colonies may contain from 50 to 400

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workers along with the founding queen Plath 1927, pp. 123124; Thorp et al.
1983, p. 2; Macfarlane et al. 1994, p. 7.
Two colonies of Franklins bumble bee that were initiated in the laboratory and set out to complete development in the field contained over 60 workers by early September, and likely produced over 100 workers by the end of the season Plowright and Stephen 1980, p. 477.
The flight season of Franklins bumble bee is from mid-May to the end of September Thorp et al. 1983, p. 30; a few individuals have been encountered in October Southern Oregon University Bee Collection records, in Xerces Society and Thorp 2010, Appendix 1, p.
39. At the end of the colony cycle, all the workers and the males die along with the founding queen; only the inseminated hibernating females gynes are left to carry on the genetic lineage into the following year Duchateau and Velthius 1988.
As with all Bombus species, Franklins bumble bee has a unique genetic system called the haplodiploid sex determination system. In this system, unfertilized haploid eggs become males that carry a single set of chromosomes, and fertilized diploid eggs become females that carry two sets of chromosomes. This system may result in lower levels of genetic diversity than the more common diploid-diploid sex determination system, in which both males and females carry two sets of chromosomes. Haplodiploid organisms may be more prone to population extinction than diploid-diploid organisms, due to their susceptibility to low population levels and loss of genetic diversity Service 2018a, p. 37.
Inbreeding depression in bumble bees can lead to the production of sterile diploid males Goulson et al. 2008, p.
11.7 and negatively affects bumble bee colony size Herrman et al. 2007, p.
1167, which are key factors in a colonys reproductive success.
As one of the rarest Bombus species, Franklins bumble bees are somewhat enigmatic, and a specific habitat study for the species has not been completed.
Such a study was initiated in 2006, when the Franklins bumble bee was last seen, but could not continue due to the subsequent absence of the species Thorp 2017, pers. comm.. However, some general habitat associations of Bombus are known. Like all bumble bees, the Franklins bumble bee requires a constant and diverse supply of flowers that bloom throughout the colonys life cycle, from spring to autumn Xerces Society and Thorp 2010, p. 11; these resources would typically be found in open non-forested meadows in proximity to seeps and other wet
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