IUCN Assessments for North American Bombus spp. for the North American IUCN Bumble Bee Specialist Group

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± Corresponding author: rich@xerces.org
* The Xerces Society for Invertebrate Conservation, 628 NE Broadway, Suite 200, Portland, OR 97232, www.xerces.org
† Department of Biology, York University, 4700 Keele Street, Toronto, Ontario M3J 1P3, Canada
‡ Gund Institute for Ecological Economics, University of Vermont, 617 Main Street Burlington, VT 05405
∆ University of California at Davis, Department of Entomology and Nematology Main Office, UC Davis Briggs Hall, Room 367,
Davis, CA 95616-5270
IUCN Assessments for North American Bombus spp.
Prepared by: Rich Hatfield*±, Sheila Colla†, Sarina Jepsen*, Leif Richardson‡, Robbin Thorp∆, and Sarah Foltz Jordan*
Assessments completed 2014
Document updated in February 2015

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TableofContents

Introducon............................................................................................................................................................. 3
Methods................................................................................................................................................................... 4
Bombusaffinis.......................................................................................................................................................... 8
Bombusappositus.................................................................................................................................................... 9
Bombusauricomus...................................................................................................................................................10
Bombusbalteatus....................................................................................................................................................11
Bombusbifarius........................................................................................................................................................12
Bombusbimaculatus................................................................................................................................................13
Bombusbohemicus..................................................................................................................................................14
Bombusborealis.......................................................................................................................................................15
Bombuscaliginosus..................................................................................................................................................16
Bombuscentralis......................................................................................................................................................17
Bombuscitrinus........................................................................................................................................................18
Bombuscrotchii........................................................................................................................................................19
Bombuscryptarum...................................................................................................................................................20
Bombusdisnguendus..............................................................................................................................................21
Bombusfervidus............................................................................................................................... ........................22
Bombusflavidus.......................................................................................................................................................23
Bombusflavifrons.....................................................................................................................................................24
Bombusfranklini......................................................................................................................................................25
Bombusfraternus.....................................................................................................................................................26
Bombusfrigidus........................................................................................................................................................27
Bombusgriseocollis............................................................................................................................... ...................28
Bombushuni..........................................................................................................................................................29
Bombushyperboreus................................................................................................................................................30
Bombusimpaens....................................................................................................................................................31
Bombusinsularis......................................................................................................................................................32
Bombusjonellus.......................................................................................................................................................33
Bombusmelanopygus..............................................................................................................................................34
Bombusmixtus.........................................................................................................................................................35
Bombusmorrisoni....................................................................................................................................................36
Bombusneoboreus...................................................................................................................................................37
Bombusnevadensis..................................................................................................................................................38
Bombusoccidentalis.................................................................................................................................................39
Bombuspensylvanicus.............................................................................................................................................40
Bombusperplexus....................................................................................................................................................41
Bombuspolaris..........................................................................................................................................................42
Bombusrufocinctus............................................................................................................................... ...................43
Bombussandersoni..................................................................................................................................................44
Bombussitkensis......................................................................................................................................................45
Bombussuckleyi.......................................................................................................................................................46
Bombussylvicola......................................................................................................................................................47
Bombusternarius.....................................................................................................................................................48
Bombusterricola......................................................................................................................................................49
Bombusvagans........................................................................................................................................................50
Bombusvandykei.....................................................................................................................................................51
Bombusvariabilis.....................................................................................................................................................52
Bombusvosnesenskii................................................................................................................................................53
References Cited...................................................................................................................................................... 54
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3
INTRODUCTION
Before detailing the methods, it is important to note that we have attempted to apply the best
possible methods to evaluate the extinction risk of North America’s bumble bees in a manner
that is consistent with the IUCN framework. A key part of the IUCN framework is assessing
changes that have occurred within the last 10 years (or 3 generations, whichever is longer). As
such, this ten year timeframe is integral to the methods we have applied and describe below.
When applying the IUCN Red List Criteria to broadly distributed invertebrates with short
lifespans, and very little to no population data, some interpretation and use of best professional
judgment is required. Some of the challenges of applying these criteria have been noted by
others, most notably Cardoso et al. (2011, 2012; but see Collen & Böhm 2012). Nevertheless, the
IUCN Red List Criteria provide the international standard for evaluating extinction risk in a
manner consistent among regions and taxonomic groups. These methods were developed in
coordination with IUCN Red List Specialists and in consultation with European colleagues who
have finished their regional Red List assessments. Please direct any questions about these
methods to Rich Hatfield at the Xerces Society (rich@xerces.org).
IUCN Red List Criteria Documents:
Full document: http://www.iucnredlist.org/documents/RedListGuidelines.pdf
This is the key document for the IUCN assessments. While the entire document is worthwhile,
the key sections that pertain to our analysis are highlighted below:
 2.2: Nature of the Categories (page 7-10)
 2.3: Nature of the criteria (page 13-15)
 3.1: Data availability, inference and projection (page 16-17)
 4.1 Population and population size (page 20)
 4.5: Reduction (criterion A) (page 25-26)
 4.9: Extent of occurrence (criteria A and B) (page 31-34)
 5-5.1: Guidelines for Applying Criteria A (page 42-44)
 10-10.3: Guidelines for Applying the Categories DD, NT, and NE (page 62-65)
Summary 1 page document: http://www.iucnredlist.org/documents/2001CatsCrit_Summary_EN.pdf
This one page document provides a summary of the five criteria used to evaluate extinction risk.

4
METHODS FOR IUCN ANALYSIS
Data set
Williams et al. (in press) assembled a database of nearly 300,000 electronic records for
specimens of North American Bombus species (sensu: Williams 2013) from academic, research,
citizen science and private collections. Most contributions to the database include records of all
Bombus held by an institution or individual, but in order to reduce bias associated with
collections, in cases where only select taxa had been digitized, we dropped that entire collection
from the database. We further removed all records lacking species-level determinations or other
essential label data. We used Google Earth and ArcGIS 10.0 (ESRI 2010) to verify, correct or
add georeference information for many records with insufficient or inaccurate location data. We
individually dropped records that were well outside the known range of a species if the
determiner could not be verified as a knowledgeable melittologist. We did not include three of
the 46 North American species (B. distinguendus, B. neoboreus and B. polaris) in these analyses
because of small sample size and/ or incomplete geographic coverage to collections. The final
dataset includes 202,198 specimen records housed in nearly 150 collections in North America
and elsewhere.
Analyses
We evaluated changes in each species’ spatial distribution over time using extent of occurrence
(EOO) and a measure of persistence (described below) We also assess changes in each species’
relative abundance, which we consider to be an ‘index of abundance relevant to the taxon’, as
specified by the IUCN Red List Categories and Criteria (IUCN 2012). For both the EOO and
persistence calculations we divided the database into historical (1805 – 2001, N=128,572) and
current (2002-2012, N=73,626) records. This timeframe was chosen as IUCN criteria stipulate
that species decline must have been observed over the longer of three generations or 10 years.
Extent of Occurrence
Since the historical database had significantly more records, and therefore could lead to an over
estimate of range loss due to an increased chance of including more records near the edge of
each species’ range, we rarefied the historic data set by randomly selecting 73,626 records from
the historical time period to use in the EOO measurement. Using z-tests for differences in
proportion, we ensured that the relative abundance of each species in the subsampled historical
data was not significantly different from the relative abundance of that species in the original
database. To measure changes in each species’ EOO, we first used a k-nearest neighbors
approach to create local convex hulls for each species in each time period (Getz et al. 2007).
Generally we used the “minimum spurious hole covering” rule proposed in Getz (Getz et al.
2007). However, since the ranges of most North America bumble bees are large, our “spurious
holes” frequently included large expanses of inhospitable habitat for bumble bees (e.g. The Gulf
of Alaska). After the local convex hull polygons were created, we clipped the polygons to the
North American continent to remove large patches of unoccupied habitat (e.g. Great Lakes).

5
Using the areas calculated from these polygons, we compared the current area to the historical
area to determine change in home range size (See individual species maps below).
Sampling Effort
Since we used presence-only records that primarily came from museum specimens for our
analysis of changes in range size, sampling effort likely played a significant role in species
presence or absence from a particular region. To account for varying sampling effort and avoid
overestimating range loss, we created sampling density rasters from the presence points of all
bumble bee species, in both the current time period and the random sample of the historical time
period (using ArcGIS 10.2). For each species we calculated the relative difference in sampling
density in areas where the EOO from the historic time period did not overlap with the EOO from
the current time period. Using the area of this non-overlapping polygon, we calculated the
average sampling density for both time periods. For species that experienced range loss in the
current time period, and had a lower sampling density than historically, we adjusted estimates of
range loss to account for the change in effort. We did not adjust the change in range estimates for
species that had a higher sampling density in the current time period.
Persistence
To determine species’ persistence within their home range, we divided the continent into 50 km
x 50 km grid cells. We used 50 km grid cells to be consistent with previous European and North
American Bombus spp. analyses (Williams et al. 2007; Colla et al. 2012) and because the data in
the historical database were georeferenced from specimen label locality descriptions, which are
sometimes inaccurate at smaller spatial scales (Wieczorek et al. 2004). For each time period we
divided the number of grid cells occupied by each species by the total number of grid cells
occupied by all species. Then, the value from the current time period was divided by the value
from the historic time period to detect changes in persistence over time. While the metric that we
report is not truly a measure of range size, it does provide a measure of each species’ persistence
within its home range.
Relative Abundance
To evaluate changes in the relative abundance (RA) of each species, we divided the full database
into historical (1805-2001) and current (2002-2012) and calculated the RA of each species in
each time period. Then, to estimate changes in RA, we divided the current RA by the historical
RA. In addition to comparing the historical time period to the most recent decade, we also broke
the database up into ten ten-year periods, plus one time period covering all records prior to 1913
and calculated the RA of each species in each time period (e.g. pre-1913 = period 1, 1913-1922
= period 2). Then, using time as the explanatory variable and RA as the independent variable,
we conducted a linear regression to assess longer-term trends in each species’ RA (see individual
species graphs). To assess extinction risk for several species we used a linear trendline to project
future declines. We used the x-intercept as the theoretical point of extinction.

6
Average Decline
To evaluate overall population trends, we calculated the mean difference between the three
measures reported above (EOO, persistence, and relative abundance) from the current time
period (2002-2012) and the historical time period (1805-2001). This measure calculates how
much the combined measures of EOO, persistence, and relative abundance have declined from
historic values. For species that have experienced an average increase from historic levels, their
average decline is reported as 0%.
IUCN Red List Categories and Criteria
We assigned each species to a preliminary IUCN Red List Category (IUCN 2012) by looking at
the quantitative measures (changes in range loss, persistence, and relative abundance), range
maps, sampling effort, recent literature, and using best professional judgment. We assigned
IUCN Red List Criteria based on the data that was available, and each species range size, as well
as the degree of confidence that we had in population estimates. Because there are limitations in
evaluating extinction risk using museum specimen data (presence-only data collected by many
individuals in a non-random manner), we generally erred on the side of categorizing a species as
less threatened than was justified by quantitative analysis alone. The selection of Red List
Categories for each species can be greatly informed (and changed, if necessary) by the field
experiences, species-specific knowledge, and collective best professional judgment of the North
American bumble bee experts.
Literature Cited (including those cited in the individual species accounts below)
Bartomeus, I., J. S. Ascher, J. Gibbs, B. N. Danforth, D. L. Wagner, S. M. Hedtke, and R. Winfree. 2013.
Historical changes in northeastern US bee pollinators related to shared ecological traits.
Proceedings of the National Academy of Sciences 110:4656–4660.
Cameron, S. A., J. D. Lozier, J. P. Strange, J. B. Koch, N. Cordes, L. F. Solter, and T. L. Griswold. 2011.
Patterns of widespread decline in North American bumble bees. Proceedings of the National
Academy of Sciences 108:662–667.
Cardoso, P., P. A. V. Borges, K. A. Triantis, M. A. Ferrández, and J. L. Martín. 2011. Adapting the IUCN
Red List criteria for invertebrates. Biological Conservation 144:2432–2440.
Cardoso, P., P. A. V. Borges, K. A. Triantis, M. A. Ferrández, and J. L. Martín. 2012. The
underrepresentation and misrepresentation of invertebrates in the IUCN Red List. Biological
Conservation 149:147–148.
Colla, S., F. Gadallah, L. Richardson, D. Wagner, and L. Gall. 2012. Assessing declines of North
American bumble bees (Bombus spp.) using museum specimens. Biodiversity and
Conservation:1–11.
Colla, S. R. 2010. COSEWIC Assessment and Status Report on the Rusty-Patched Bumble Bee Bombus
affinis in Canada. Ottawa: Committee on the Status of Endangered Wildlife in Canada.
Collen, B., and M. Böhm. 2012. The growing availability of invertebrate extinction risk assessments–A
response to Cardoso et al.(October 2011): Adapting the IUCN Red List criteria for invertebrates.
Biological Conservation.

7
Getz, W. M., S. Fortmann-Roe, P. C. Cross, A. J. Lyons, S. J. Ryan, and C. C. Wilmers. 2007. LoCoH:
nonparameteric kernel methods for constructing home ranges and utilization distributions. PloS
one 2:e207.
IUCN. 2012. IUCN Red List categories and criteria: Version 3.1Second. IUCN Species Survival
Commision, Gland, Switzerland and Cambridge, UK. Retrieved from
http://jr.iucnredlist.org/documents/redlist_cats_crit_en.pdf.
Thorp, R., K. Strickler, and J. Cane. 2003. Bumble bees (Hymenoptera: Apidae): commercial use and
environmental concerns. For nonnative crops, whence pollinators of the future:21–40.
Thorp, R. W. 2005. Franklin’s bumble bee, Bombus franklini (Frison 1921): a species of special concern.
Report to US Fish and Wildlife Service, Portland, OR on 2005 season (submitted 7 November
2005).
Thorp, R. W., S. Jepsen, S. F. Jordan, E. Evans, and S. H. Black. 2010. Petition to list Franklin’s bumble
bee Bombus franklini (Frison), 1921 as an Endangered Species under the U.S. Endangered
Species Act.
Thorp, R. W., and M. D. Shepherd. 2005. Profile: Subgenus Bombus. Red list of pollinator insects of
North America.
Wieczorek, J., Q. Guo, and R. Hijmans. 2004. The point-radius method for georeferencing locality
descriptions and calculating associated uncertainty. International journal of geographical
information science 18:745–767.
Williams, P. 2013. Bumble Bees of the World. Research group. Retrieved May 8, 2013, from
http://www.nhm.ac.uk/research-curation/research/projects/bombus/.
Williams, P. H., M. B. Araújo, and P. Rasmont. 2007. Can vulnerability among British bumblebee
(Bombus) species be explained by niche position and breadth? Biological Conservation 138:493–
505.
Williams, P. H., R. W. Thorp, L. L. Richardson, and S. R. Colla. 2014. Bumble bees of North America:
an identifcation guide. Princeton University Press.

Species: Bombus anis
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 54.68%
Persistence in current range relave to historic occupancy: 29.77%
Current relave abundance relave to historic values: 7.46%
Average decline: 69.36%
Preliminary IUCN Category: Crically Endangered, Endangered; CR,
EN
IUCN Criteria: CR A2b; EN A2c
Juscaon (Notes): Historically common and broadly distributed in
the Upper Midwest and Eastern North America, Bombus anis has recently experienced serious declines in relave abundance,
persistence and distribuon across its range. Despite dramacally increased awareness and survey eort for B. anis, numerous
regional studies have reported local exrpaons and declines in this species (reviewed in Jepsen et al. 2013), and range-wide stud-
ies have found relave abundance declines up to 95% (Cameron et al. 2011a), and range losses of 70 to 87% in recent years
(Colla et al. 2012, Cameron et al. 2011a). Consistent with these ndings, our analysis found B. anis has exhibited a 92.54% relave
abundance decline over the past decade, suggesng a Crically Endangered Red List category for this species. Note that the Aver-
age Decline of 69.36% (based on relave abundance, persistence, and range loss) points toward an Endangered Red List category
(very near the cut-o for Crically Endangered). Since the range loss detected in our analysis (45.32%) is much lower than that re-
ported in other studies (87% in Cameron et al. 2011a, considering only the U.S. range; 70% in Colla et al. 2012, considering U.S. and
Canada range), we elected to use the Relave Abundance Decline to esmate Past Reducon, rather than Average Decline. This
species is listed as Endangered in Canada (COSEWIC 2010) and has been peoned for Endangered Species Lisng in the United
States (Jepsen et al. 2013). Based on our recent analysis, along with published reports of bumble bee decline and the assessors'
best professional judgment, we recommend this species for the Crically Endangered Red List category at this me.
Figure 1: Relave abundance trends of Bombus anis
Figure 2: Map used to measure range decline for Bombus anis
8

Species: Bombus appositus
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 82.57%
Persistence in current range relave to historic occupancy: 85.57%
Current relave abundance relave to historic values: 46.65%
Average decline: 28.40%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): According to our analysis, this western North
American species has not experienced serious declines in recent
years. In our analysis, the average decline of 28.40% (inuenced largely by relave abundance decline) suggests that this species
qualies as Near Threatened based on criterion A2. However, while this species' relave abundance has been declining since a high
peak in the 1960s-70s, it has increased in last decade compared to the decade prior, and over a long me period, the relave abun-
dance regression is essenally at. Extent of occurrence (EOO) and persistence declines have been minimal. We have condence in
the EOO decline in the western poron of this species' range, since there has been signicant sampling eort in these areas in the
past decade, but more sampling is needed in northeastern and southeastern porons of its range. Much of this species' range is in
under-sampled areas, except for a few pockets with high survey eort where this species is generally well-represented. Overall,
based on the above calculaons and trends, along with published reports of bumble bee decline and the assessors' best profession-
al judgment, including eld experience of several western bumble bee experts, we recommend this species for the Least Concern
Red List category at this me.
Figure 1: Relave abundance trends of Bombus appositus
Figure 2: Map used to measure range decline for Bombus appositus
9

Species: Bombus auricomus
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 88.62%
Persistence in current range relave to historic occupancy: 88.98%
Current relave abundance relave to historic values: 50.08%
Average decline: 24.11%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): This species occurs broadly throughout the
eastern United States and Canada. In our analysis, the average de-
cline of 24.11% suggests that this species qualies as Near Threatened based on criterion A2. However, since the bulk of the range
loss for this species was in the Great Plains, which has generally been poorly sampled, we recommend a Least Concern Red List
Category at this me. This species is common in areas was sampling eort has been high. This is consistent with a number of stud-
ies suggesng that this species is common and relavely abundant in much of its range (e.g., Grix et al. 2009, Hines and Hendrix
2005, Johnson 2009, Colla et al. 2012). Based on the above calculaons and trends, along with published reports of bumble bee
decline and the assessors' best professional judgment, we recommend this species for the Least Concern Red List category at this
me.
Figure 1: Relave abundance trends of Bombus auricomus
Figure 2: Map used to measure range decline for Bombus auricomus
10

Species: Bombus balteatus
Assessment Level: Regional
Status: Delayed for taxonomic status
Current range size relave to historic range: 69.58%
Persistence in current range relave to historic occupancy: 103.00%
Current relave abundance relave to historic values: 34.61%
Average decline: 30.93%
Preliminary IUCN Category: Data Decient; DD
IUCN Criteria:
Juscaon (Notes): This high-elevaon species has been under-
surveyed and its status is poorly known in both Europe and North
America. According to Haield et al. (2014), there is a lack of recent and historic sampling in the majority of this species' North
American range (especially the northern part), which makes each of the measures (EOO, persistence, relave abundance, and aver-
age decline) dicult to interpret. Climate change is a threat throughout this species' range, but specic climate-driven impacts to
this species have not been documented. More informaon in North America is needed to evaluate threat and potenal decline.
Figure 1: Relave abundance trends of Bombus balteatus
Figure 2: Map used to measure range decline for Bombus balteatus
11

Species: Bombus bifarius
Assessment Level: Global
Status: Published
Current range size relave to historic range: 119.78%
Persistence in current range relave to historic occupancy: 94.13%
Current relave abundance relave to historic values: 126.53%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): This widespread species is common across
most of its range and has increased in both relave abundance and
range in the last decade (2002-2012). Our analyses indicate it should be classied as Least Concern.
Figure 1: Relave abundance trends of Bombus bifarius
Figure 2: Map used to measure range decline for Bombus bifarius
12

Species: Bombus bimaculatus
Assessment Level: Global
Status: Published
Current range size relave to historic range: 96.56%
Persistence in current range relave to historic occupancy: 204.77%
Current relave abundance relave to historic values: 188.19%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): Our analysis is consistent with other studies
which show this eastern North American bumble bees remains com-
mon, is increasing in relave abundance in some areas, and is not of conservaon concern. Based on the above calculaons and
trends, along with published reports of bumble bee decline and the assessors' best professional judgment, we recommend this
species for the Least Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus bimaculatus
Figure 2: Map used to measure range decline for Bombus bimaculatus
13

Species: Bombus bohemicus
Assessment Level: Regional
Status: Delayed for cross-connental distribuon
Current range size relave to historic range: 3.72%
Persistence in current range relave to historic occupancy: 9.16%
Current relave abundance relave to historic values: 2.82%
Average decline: 94.77%
Preliminary IUCN Category: Crically Endangered; CR
IUCN Criteria: A2bc
Juscaon (Notes): This cuckoo bumble bee occurs in only approxi-
mately 7 sites now. Its populaon reducon is suspected to have
been >80% in the past decade based on a 97.18% decline in relave abundance between recent (2002-2012) and historic (1805-
2001) me periods and a 96.28% decline in EOO between recent & historic me periods. Since this Psithyrus species uses
both Bombus terricola and B. anis as hosts and we know that there has been a decline in the availability of these hosts, we can
apply criterion A2c (decline in habitat quality). We are not comfortable using criteria C & D since historic sites have not been revisit-
ed and we lack populaon level data. This review includes Bombus ashtoni (Haield et al. 2014.)
Figure 1: Relave abundance trends of Bombus bohemicus
Figure 2: Map used to measure range decline for Bombus bohemicus
14

Species: Bombus borealis
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 92.98%
Persistence in current range relave to historic occupancy: 98.78%
Current relave abundance relave to historic values: 86.91%
Average decline: 7.11%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): Our analysis suggests that this eastern North
American species has not experienced serious declines over the last
decade. Specically, the average decline of 7.11% (based on relave abundance, range, and persistence) suggests a Least Concern
category for this species. This is consistent with ndings from other studies in which signicant declines in this species have not
been found (e.g., Colla and Packer 2008, Colla et al. 2012). Based on the above calculaons and trends, along with published re-
ports of bumble bee decline and the assessors' best professional judgment, we recommend this species for the Least Concern Red
List category at this me.
Figure 1: Relave abundance trends of Bombus borealis
Figure 2: Map used to measure range decline for Bombus borealis
15

Species: Bombus caliginosus
Assessment Level: Global
Status: Published
Current range size relave to historic range: 58.75%
Persistence in current range relave to historic occupancy: 33.69%
Current relave abundance relave to historic values: 15.60%
Average decline: 63.99%
Preliminary IUCN Category: Vulnerable; VU
IUCN Criteria: A2bc
Juscaon (Notes): These analyses suggest very high populaon
decline range-wide, including range size reducons, persistence re-
ducons, and relave abundance declines. The EOO and relave abundance values suggest an EN (Endangered) Red List category,
but we have quesons about the sampling eort that has occurred in the past decade within this species' historic range. More sur-
veys are needed within this species' historic range. This is parcularly true because this species co-occurs with Bombus vosnesenskii
(a very common bee that is dicult to discern from B. caliginosus in the eld) and many collectors/observers may miss this species
because of that. In light of this, we are recommending this species for Vulnerable (rather than Endangered) Red List category.
Figure 1: Relave abundance trends of Bombus caliginosus
Figure 2: Map used to measure range decline for Bombus caliginosus
16

Species: Bombus centralis
Assessment Level: Global
Status: Published
Current range size relave to historic range: 107.48%
Persistence in current range relave to historic occupancy: 88.61%
Current relave abundance relave to historic values: 81.27%
Average decline: 7.55%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): This species is widely distributed across the
Mountain West and does not appear to have undergone range con-
stricon in recent years, nor has relave abundance declined dramacally. This nding is consistent with other reports that this
species is moderately common in most of its range (Williams et al. 2014). Specic threats have not been idened for this species.
Our analysis of populaon trends, published reports of bumble bee decline, along with the assessors' best professional judgment,
lead us to recommend this species for the Least Concern Red List category.
Figure 1: Relave abundance trends of Bombus centralis
Figure 2: Map used to measure range decline for Bombus centralis
17

Species: Bombus citrinus
Assessment Level: Global
Status: Published
Current range size relave to historic range: 98.54%
Persistence in current range relave to historic occupancy: 124.16%
Current relave abundance relave to historic values: 130.12%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): According to our analyses, this eastern North
American bumble bee has not declined in distribuon or relave
abundance in the past decade. This is consistent with other studies, e.g. Colla et al. (2012), which found high persistence of this
species in historically occupied areas, and no signicant declines in relave abundance over the me periods examined. Note that
the abundance and distribuon in this species likely depend on abundance and distribuon of host species, which remain common.
Based on the above calculaons and trends, along with published reports of bumble bee decline and the assessors' best profession-
al judgment, we recommend this species for the Least Concern Red List category at this me. Subgenus Psithyrus, hosts= B. bimac-
ulatus, B. impaens, and B. vagans.
Figure 1: Relave abundance trends of Bombus citrinus
Figure 2: Map used to measure range decline for Bombus citrinus
18

Species: Bombus crotchii
Assessment Level: Regional
Status: IUCN Accepted
Current range size relave to historic range: 74.67%
Persistence in current range relave to historic occupancy: 20.48%
Current relave abundance relave to historic values: 2.32%
Average decline: 67.51%
Preliminary IUCN Category: Endangered; EN
IUCN Criteria: EN A2bc
Juscaon (Notes): This species is limited in distribuon to south-
western North America. It was historically common in the Central
Valley of California, but now appears to be absent from most of it, especially in the center of its historic range. The past decline of
67.51% (based on EOO, persistence, and relave abundance) suggests that this species should be listed as Endangered (EN) using
criteria A2bc. The A2c criterion includes a decline in habitat quality; in the northern Central Valley there has been extensive agricul-
tural intensicaon and the southern part of its range is experiencing rapid urbanizaon. Note that recent collecon eort has not
been sucient throughout this species' historic range, although there has been a moderate level of sampling in the recent dec-
ade. Based on the above calculaons and trends, along with published reports of bumble bee decline and the assessors' best pro-
fessional judgment, we recommend this species for the Endangered Red List category at this me.
Figure 1: Relave abundance trends of Bombus crotchii
Figure 2: Map used to measure range decline for Bombus crotchii
19

Species: Bombus cryptarum
Assessment Level: Global
Status: Delayed for cross-connental distribuon
Current range size relave to historic range: 28.94%
Persistence in current range relave to historic occupancy: 268.16%
Current relave abundance relave to historic values: 71.87%
Average decline: 0.00%
Preliminary IUCN Category: Data Decient; DD
IUCN Criteria:
Juscaon (Notes): In North America, recent analysis suggests that
this species remains common throughout its range, and has in-
creased in relave abundance. The average decline of 0% suggests a Least Concern category for this species in North America. Simi-
larly, in Europe, the regional IUCN Assessment for B. cryptarum lists this species as Least Concern in view of its "wide distribu-
on, presumed large overall populaon and no major threats". However, addional research should be conducted to determine
the populaon trend of this species in Europe, and the status of this species in Asia. Based on the above calculaons and trends,
along with published reports of bumble bee decline and the assessors' best professional judgment, we recommend this species for
the Data Decient Red List category at this me.
Figure 1: Relave abundance trends of Bombus cryptarum
Figure 2: Map used to measure range decline for Bombus cryptarum
20

Species: Bombus disnguendus
Assessment Level:
Status: Delayed for cross-connental distribuon
Current range size relave to historic range: 0.00%
Persistence in current range relave to historic occupancy:
Current relave abundance relave to historic values: 3789.38%
Average decline: 0.00%
Preliminary IUCN Category: Data Decient; DD
IUCN Criteria:
Juscaon (Notes): In North America, there are only 23 total records in the database from this species. This is not enough data to
build EOO polygons or analyze changes in relave abundance, persistence, or range. North American data points toward a Data
Decient Red List Category at this me. In Europe, the regional IUCN Assessment for this species lists it as Vulnerable due to an
esmated populaon decline of over 30% in the last ten years, based on decline in the area of occupancy (AOO) and extent of oc-
currence (EOO). European declines are linked to habitat loss and changes in agricultural pracces (especially removal of the majori-
ty of clover elds that this species needs for forage) in the region (European IUCN Assessment).
Figure 2: Map used to measure range decline for Bombus disnguendus
21

Species: Bombus fervidus
Assessment Level: Global
Status: Submied
Current range size relave to historic range: 86.98%
Persistence in current range relave to historic occupancy: 85.84%
Current relave abundance relave to historic values: 38.04%
Average decline: 29.71%
Preliminary IUCN Category: Vulnerable; VU
IUCN Criteria: A2b
Juscaon (Notes): A number of studies have demonstrated abun-
dance and persistence declines in this eastern North American spe-
cies (e.g., Colla et al. 2012, Colla and Packer 2008, Giles and Ascher 2006). Consistent with these studies, our analysis shows decline
in relave abundance over the me period examined, as well as long term steady decline. If this species' relave abundance conn-
ues to decline at the same rate, we project that the species will go exnct in the next 70 to 80 years. The most recent me period
shows the lowest relave abundance of all me periods. The relave abundance decline in the past decade has been nearly 50%
from mean. Although the persistence value is relavely high and the EOO loss has not been that great, the changes in relave
abundance jusfy the Vulnerable category. Based on the above calculaons and trends, along with published reports of bumble
bee decline and the assessors' best professional judgment, we recommend this species for the Vulnerable Red List category at this
me. Includes B. californicus.
Figure 1: Relave abundance trends of Bombus fervidus
Figure 2: Map used to measure range decline for Bombus fervidus
22

Species: Bombus avidus
Assessment Level: Global
Status: Delayed for cross-connental distribuon
Current range size relave to historic range: 68.58%
Persistence in current range relave to historic occupancy: 95.39%
Current relave abundance relave to historic values: 64.53%
Average decline: 23.83%
Preliminary IUCN Category: Least Concern; LC (Regionally) DD Glob-
ally
IUCN Criteria:
Juscaon (Notes): In North America, this species has not experi-
enced serious declines in relave abundance, persistence, or range in recent years. The average decline value of 23.83%, along with
published reports of bumble bee decline and the assessors' best professional judgment, suggest a Least Concern Red List category
in this region.
In Europe, this species is also recommended for the Least Concern Red List category, in light of its wide distribuon, presumed
large overall populaon with a stable populaon trend, and no major threats.
In Asia, the distribuon and populaon status of this species are unknown, and the importance of Asian populaons to the overall
species security is unclear. As such, we recommend this species for a Data Decient Red List Category at this me.
Figure 1: Relave abundance trends of Bombus avidus
Figure 2: Map used to measure range decline for Bombus avidus
23

Species: Bombus avifrons
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 79.45%
Persistence in current range relave to historic occupancy: 131.91%
Current relave abundance relave to historic values: 161.79%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): Our analysis suggests that this western North
American species has not experienced declines in relave abun-
dance, range, or persistence in recent years. Specically, the average decline of 0% suggests a Least Concern category for this spe-
cies. This nding is consistent with other reports of this species being common throughout its range (Williams et al. 2014). Based on
the above calculaons and trends, along with published reports of bumble bee decline and the assessors' best professional judg-
ment, we recommend this species for the Least Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus avifrons
Figure 2: Map used to measure range decline for Bombus avifrons
24

Species: Bombus franklini
Assessment Level: Global
Status: Published
Current range size relave to historic range: 55.55%
Persistence in current range relave to historic occupancy: 32.84%
Current relave abundance relave to historic values: 15.38%
Average decline: 65.41%
Preliminary IUCN Category: Crically Endangered; CR
IUCN Criteria: A2abce, B1ab, B2ab, C2ai, D
Juscaon (Notes): R.W. Thorp’s unpublished surveys have re-
vealed that, since 1998, the populaons have decreased to the point
of being not seen at all in 2004 or 2005, with only one individual found in 2006. Because extensive surveys of the area within which
B. franklini exists have, as of 2006, uncovered only one individual, but similar surveys in the rst three years (1998-2000) uncovered
individuals at many historic and seven new sites, it can be concluded that the extent of populaon is decreasing severely. Though
further invesgaon would be required to determine the exact number of extant B. franklini, based on their limited range, it can be
assumed that their populaons are decreasing to dangerously low levels, and therefore need protecon, which it has not yet legal-
ly received.
Figure 1: Relave abundance trends of Bombus franklini
Figure 2: Map used to measure range decline for Bombus franklini
25

Species: Bombus fraternus
Assessment Level: Global
Status: Published
Current range size relave to historic range: 71.38%
Persistence in current range relave to historic occupancy: 43.33%
Current relave abundance relave to historic values: 14.40%
Average decline: 56.96%
Preliminary IUCN Category: Endangered; EN
IUCN Criteria: ENA2b, VUA2c
Juscaon (Notes): According to our analysis, this North American
species has exhibited declines in relave abundance and EOO over
the past decade. In addion, this species' long-term downward trend in relave abundance is near signicant; if the same rate of
decline in relave abundance connues, this species could potenally go exnct within 80-90 years. There are huge gaps in recent
(as well as historic) collecon eort, especially in Oklahoma, Kansas, Nebraska, western Texas, and the Dakotas, yet there has been
signicant range loss in the northern and southern parts of its range where collecon eort has been more consistent. Thus, we
have high condence in the EOO decline of 28.62%, probably due to habitat alteraons. We selected criterion A2bc based on a de-
cline in Relave Abundance, EOO, and habitat quality. Habitat modicaon over the past 10 years (inseccide use, grassland con-
version to agriculture) has been severe in the region where this species occurs (Haield et al. 2014.). These results are consistent
with other ndings of decline in this species (e.g. Colla et al. 2012, Grix et al. 2009). Based on the above calculaons and trends,
along with published reports of bumble bee decline and the assessors' best professional judgment, we recommend this species for
the Endangered Red List category at this me.
Figure 1: Relave abundance trends of Bombus fraternus
Figure 2: Map used to measure range decline for Bombus fraternus
26

Species: Bombus frigidus
Assessment Level: Global
Status: Published
Current range size relave to historic range: 39.69%
Persistence in current range relave to historic occupancy: 161.88%
Current relave abundance relave to historic values: 116.34%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): According to our analyses, this widely distrib-
uted northern North American species has not declined in relave
abundance or persistence measures, over the me period examined. Although the EOO measure shows a 60.31% loss, many of the
areas that the species has apparently been lost from haven't been sampled in the recent me period. It has been found in most
areas that have been re-sampled in the recent me period. Based on the above calculaons and trends, along with published re-
ports of bumble bee decline and the assessors' best professional judgment, we recommend this species for the Least Concern Red
List category at this me.
Figure 1: Relave abundance trends of Bombus frigidus
Figure 2: Map used to measure range decline for Bombus frigidus
27

Species: Bombus griseocollis
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 90.21%
Persistence in current range relave to historic occupancy: 166.87%
Current relave abundance relave to historic values: 215.25%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): Our analysis suggests that this North American
species remains common through its range, and has increased in
relave abundance. The average decline of 0% suggests a Least Concern category for this species. Based on the above calculaons
and trends, along with published reports of bumble bee decline and the assessors' best professional judgment, we recommend this
species for the Least Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus griseocollis
Figure 2: Map used to measure range decline for Bombus griseocollis
28

Species: Bombus huni
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 92.49%
Persistence in current range relave to historic occupancy: 60.98%
Current relave abundance relave to historic values: 70.51%
Average decline: 25.34%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): According to our analyses, this western North
American species has not exhibited notable declines over the me
period examined. Based on the average decline of 25.34%, this species qualies as Near Threatened using criterion A2. However,
since this is one of the more common bees in the intermountain west, and since the extent of occurrence (EOO) decline (apparent
range loss) has primarily occurred in under-sampled areas, we are not comfortable using the Near Threatened category. Based on
the calculaons and trends in Haield et al. (2014), along with published reports of bumble bee decline and the assessors' best
professional judgment, we recommend this species for the Least Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus huni
Figure 2: Map used to measure range decline for Bombus huni
29

Species: Bombus hyperboreus
Assessment Level: Regional
Status: Delayed for taxonomic status
Current range size relave to historic range: 0.00%
Persistence in current range relave to historic occupancy: 27.01%
Current relave abundance relave to historic values: 38.82%
Average decline: 78.06%
Preliminary IUCN Category: Data Decient; DD
IUCN Criteria: N/A
Juscaon (Notes): In Europe, this species is listed as Vulnerable,
based on a connuing decline in the extent of occurrence, the area
of occupancy and the number of mature individuals. The species is experiencing extreme uctuaons in the number of mature indi-
viduals. It's status as an inquiline (cuckoo bee) in the nests of other bumble bees, including the declining B. polaris, is likely to inu-
ence populaon stability. Although the known area of occupancy (AOO) is 420 km², it is believed that the species occupies a larger
area in Europe, but sll less than 2,000 km².
In North America, the average decline of 78.06% (based on range, persistence, and relave abundance decline) points toward an
Endangered Red List Category, however the region where this species occurs has been under-sampled in both historic and current
me periods, making assessment of populaon trends dicult. As such, North American assessors suggest a Data Decient Red List
Category for this region.
Figure 1: Relave abundance trends of Bombus hyperboreus
Figure 2: Map used to measure range decline for Bombus hyperboreus
30

Species: Bombus impaens
Assessment Level: Global
Status: Published
Current range size relave to historic range: 97.50%
Persistence in current range relave to historic occupancy: 158.62%
Current relave abundance relave to historic values: 294.17%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): Bombus impaens is one of the most wide-
spread and abundant species in the Eastern United States and adja-
cent Canada, and appears to be expanding in range due to accidental escapes of managed colonies into the wild, outside of the
species' nave range. Consistent with other studies, our analyses do not show declines in this species range, persistence, or relave
abundance. Based on the above calculaons and trends, along with published reports of bumble bee decline (e.g., Colla et al. 2012)
and the assessors' best professional judgment, we recommend this species for the Least Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus impaens
Figure 2: Map used to measure range decline for Bombus impaens
31

Species: Bombus insularis
Assessment Level: Global
Status: Published
Current range size relave to historic range: 89.31%
Persistence in current range relave to historic occupancy: 86.28%
Current relave abundance relave to historic values: 87.29%
Average decline: 12.37%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): Declines in abundance or range of this widely
distributed North American species have been relavely low, range-
wide. Based on the above calculaons and trends, along with published reports of bumble bee decline and the assessors' best pro-
fessional judgment, we recommend this species for the Least Concern Red List category at this me. Note, however, that this spe-
cies should be frequently re-evaluated for any populaon changes and threats. This is parcularly important since this species has
declined in some parts of its range, and since it is dependent upon strong populaons of its' host bees for survival, many of which
are in decline. In the subgenus Psithyrus; hosts=B. rufocinctus, B. ternarius, B. terricola, B. occidentalis, B. nevadensis, B. californi-
cus (=fervidus), B. appositus; however, it seems to have disappeared from northern part of its range in Great Lakes area, southern
Ontario.
Figure 1: Relave abundance trends of Bombus insularis
Figure 2: Map used to measure range decline for Bombus insularis
32

Species: Bombus jonellus
Assessment Level: Regional
Status: Delayed for cross-connental distribuon
Current range size relave to historic range: 35.83%
Persistence in current range relave to historic occupancy: 198.31%
Current relave abundance relave to historic values: 294.02%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): In Europe, this species is listed as Least Con-
cern in view of its wide distribuon, presumed large overall popula-
on, and stable populaon trend (European IUCN Assessment). In North America, this species has apparently increased in relave
abundance and persistence, while declining in range in recent years. Haield et al. (2014) note that there are very few historic rec-
ords of this species; interesngly, the historic range is three mes larger even though there are 1/3 as many historic records as cur-
rent records. Overall, the average decline value of 23.83% over the past decade suggests a Least Concern Red List category in this
region. In Asia, the distribuon and populaon status of this species are unknown, and the importance of Asian populaons to the
overall species security is unclear. As such, we recommend this species for a Data Decient Red List Category at this me.
Figure 1: Relave abundance trends of Bombus jonellus
Figure 2: Map used to measure range decline for Bombus jonellus
33

Species: Bombus melanopygus
Assessment Level: Global
Status: Published
Current range size relave to historic range: 71.48%
Persistence in current range relave to historic occupancy: 99.33%
Current relave abundance relave to historic values: 81.85%
Average decline: 15.78%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): This somewhat widespread western North
American species is apparently common across most of its range,
and has not been found to be exhibing serious decline in either range or relave abundance. Our analyses indicate it should be
classied as Least Concern at this me.
Figure 1: Relave abundance trends of Bombus melanopygus
Figure 2: Map used to measure range decline for Bombus melanopygus
34

Species: Bombus mixtus
Assessment Level: Global
Status: Published
Current range size relave to historic range: 51.94%
Persistence in current range relave to historic occupancy: 141.35%
Current relave abundance relave to historic values: 263.61%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): This North American species is consid-
ered moderately common throughout its mostly Western range
(Williams et al. 2014), and was not found to have undergone declines in our analyses. Based on the above calculaons and trends,
along with published reports of bumble bee decline and the assessors' best professional judgment, we recommend this species for
the Least Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus mixtus
Figure 2: Map used to measure range decline for Bombus mixtus
35

Species: Bombus morrisoni
Assessment Level: Global
Status: Published
Current range size relave to historic range: 81.87%
Persistence in current range relave to historic occupancy: 27.49%
Current relave abundance relave to historic values: 17.43%
Average decline: 57.74%
Preliminary IUCN Category: Near Threatened; NT
IUCN Criteria:
Juscaon (Notes): This western North American species has de-
clined in relave abundance by 82.57% over the past ten years, and
persistence declines have also been high (>70%). The EOO appears relavely stable, since most declines have been in the interior
of the species' range. Note that the Intermountain West, which is the heart of this species' range, is generally an under-sampled
area. However, there are large areas within this region that appear to have been well-sampled in recent years with limited detec-
on of this species, e.g., western Nevada and the Four Corners area (see aached map, from Haield et al. 2014). R. Thorp (pers.
comm. 2014) notes the absence of this species in recent surveys at the well-surveyed Southwestern Research Staon in Arizona. In
other well-sampled areas of Utah, this species appears to be maintaining high numbers (J. Strange and T. Griswold pers
comm. 2014). More research is needed to evaluate the status of this species throughout its range, especially eastern Oregon and
Washington, and western Nevada. Overall, this species is uncommon, and appears to be declining in parts of its range (Williams et
al. 2014, Haield et al. 2014). Although our analysis points towards a Red List status of Endangered for this species, we are recom-
mending Vulnerable at this me, in light of the various uncertaines presented above (e.g. limited sampling in parts of the species'
range; changes in habitats sampled in some areas; and apparent security of this species at a few known sites).
Figure 1: Relave abundance trends of Bombus morrisoni
Figure 2: Map used to measure range decline for Bombus morrisoni
36

Species: Bombus neoboreus
Assessment Level:
Status: Delayed for taxonomic status
Current range size relave to historic range: 0.00%
Persistence in current range relave to historic occupancy:
Current relave abundance relave to historic values: 0.00%
Average decline: 0.00%
Preliminary IUCN Category: Data Decient; DD
IUCN Criteria:
Juscaon (Notes): The distribuon of this species is restricted to far northern North America, where collecon has been limited.
There are only 57 known records for this species. This is not enough data to build EOO polygons or analyze relave abundance for
this species. Addional surveys for this species are needed. As such, we recommend the Data Decient Red List category at this
me.
Figure 2: Map used to measure range decline for Bombus neoboreus
37

Species: Bombus nevadensis
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 104.71%
Persistence in current range relave to historic occupancy: 84.78%
Current relave abundance relave to historic values: 64.08%
Average decline: 15.48%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): According to our analysis, this western North
American species has not declined signicantly in range, persistence,
or abundance over the me period examined. Specically, the average decline of 15.48% suggests a Least Concern category for this
species. Similarly, reports from the literature do not suggest recent threats or declines in this species (NatureServe 2014). Based on
the above calculaons and trends, along with published reports of bumble bee decline and the assessors' best professional judg-
ment, we recommend this species for the Least Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus nevadensis
Figure 2: Map used to measure range decline for Bombus nevadensis
38

Species: Bombus occidentalis
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 77.96%
Persistence in current range relave to historic occupancy: 72.56%
Current relave abundance relave to historic values: 28.51%
Average decline: 40.32%
Preliminary IUCN Category: Vulnerable; VU
IUCN Criteria: A2be
Juscaon (Notes): Historically broadly distributed in western
North America, Bombus occidentalis has experienced serious de-
clines in relave abundance, persistence, and range in recent years (Haield et al. 2014, Cameron et al. 2011a, Thorp 2008). The
average decline value of 40.32% over the past decade (based on relave abundance, persistence, and range declines) suggests a
Vulnerable Red List Category for this species. This nding, along with published reports of bumble bee decline and the assessors'
best professional judgment, leads us to recommend this species for the Vulnerable Red List category at this me. The use of criteri-
on A2b (where populaon reducon is suspected) can be jused by changes in relave abundance. Criterion A2e may be jused
by the potenal eects of pathogens or parasites on B. occidentalis populaons (e.g., Cameron et al. 2011a).
Figure 1: Relave abundance trends of Bombus occidentalis
Figure 2: Map used to measure range decline for Bombus occidentalis
39

Species: Bombus pensylvanicus
Assessment Level: Regional
Status: Submied
Current range size relave to historic range: 81.18%
Persistence in current range relave to historic occupancy: 53.24%
Current relave abundance relave to historic values: 11.44%
Average decline: 51.38%
Preliminary IUCN Category: Vulnerable; VU
IUCN Criteria: A2be
Juscaon (Notes): Bombus pensylvanicus EOO decline is most
severe in northern areas, which have been well sampled (although it
doesn't look like this species was ever that abundant in those northern areas). Its relave abundance trend has been slowly moving
downward unl recently, when the downward trend has become much sharper (but is not stascally signicant). The Cameron
study esmates a 23% range loss, we found a range loss of ~50% along with a 50% drop in persistence and 88.56% drop in relave
abundance for this species. [We used the A2c criterion for EOO for B. morrisoni; although these two species have similar esmates
for EOO decline, we decided not to use EOO criteria for B. pensylvanicus because it has such a large historic range that includes so
many areas that have not been well sampled recently]. Criterion A2e was used for: "populaon reducon suspected based upon
eects of introduced pathogens or parasites" (Cameron et al. 2011 - this study showed a signicantly higher prevalence of individu-
als infected with N. bombi than stable species - 15.2% of individuals collected were infected). This review includes B. sonorus.
Based on the above calculaons and trends, along with published reports of bumble bee decline and the assessors' best profession-
al judgment, we recommend this species for the Vulnerable Red List category at this me.
Figure 1: Relave abundance trends of Bombus pensylvanicus
Figure 2: Map used to measure range decline for Bombus pensylvanicus
40

Species: Bombus perplexus
Assessment Level: Global
Status: Published
Current range size relave to historic range: 93.97%
Persistence in current range relave to historic occupancy: 166.31%
Current relave abundance relave to historic values: 92.19%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): According to our analysis, this North American
species has not experienced serious declines in relave abundance,
persistence, or range in recent years. This nding is consistent with other studies that have found this species to be relavely sta-
ble, both regionally and range-wide (e.g. Colla et al. 2012, Colla and Packer 2008, Grix et al. 2009). Based on the above calcula-
ons and trends, along with published reports of bumble bee decline and the assessors' best professional judgment, we recom-
mend this species for the Least Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus perplexus
Figure 2: Map used to measure range decline for Bombus perplexus
41

Species: Bombus polaris
Assessment Level:
Status: Delayed for taxonomic status
Current range size relave to historic range: 0.00%
Persistence in current range relave to historic occupancy:
Current relave abundance relave to historic values: 0.00%
Average decline: 0.00%
Preliminary IUCN Category: Data Decient; DD
IUCN Criteria:
Juscaon (Notes): The species has a moderately wide distribuon
within northern parts of Pan Europe and North America, although it
is restricted to areas above the tree line, in tundra and open habitats. The area of occupancy (AOO) is 700 km2 and 328 km2 for
Europe and the EU 27 respecvely, based on currently known records. Although the species is believed to occupy a larger area, the
AOO for both Europe and EU 27 is certainly less than 2,000 km2. The species has experienced a strong decline in its populaon in
Scandinavia since 2010, a decline that may have been repeated in parts of European Russia (Filippov 2014). The species is consid-
ered to be undergoing extreme uctuaons in the number of mature individuals due to the unpredictable occurrence of heatwaves
in Arcc Scandinavia; the situaon in European Russia is not known, but is expected to be similar. In Europe, this species is recom-
mended for the Vulnerable Red List Category, based on a connuing decline in AOO, the extent and quality of habitat, and in the
number of mature individuals (European IUCN Assessment).
In North America, there are just 46 records of this species from the current me period, and the enrety of this species' range has
been relavely under sampled in both historic and current me periods, making assessment of populaon trends dicult. More
research throughout this species' range is needed. As such, North American assessors suggest a Data Decient Red List Category for
this region.
Figure 1: Relave abundance trends of Bombus polaris
Figure 2: Map used to measure range decline for Bombus polaris
42

Species: Bombus rufocinctus
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 91.45%
Persistence in current range relave to historic occupancy: 106.47%
Current relave abundance relave to historic values: 154.88%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): According to our analysis, this widespread
North American species has not exhibited range-wide decline in re-
cent years. Specically, the average decline of 0% (based on relave abundance, persistence, and range) suggests a Least Concern
category for this species. Note that this analysis did not consider the Mexican distribuon of this species, however, since this spe-
cies is known from very few records in a small area of Mexico (Labougle 1990, ECOSUR 2014), the Mexican data would not have
signicantly impacted the above results. Our ndings are consistent with other reports that the species is stable or increasing
throughout the eastern and central porons of its range (Colla and Packer 2008, Grix et al. 2009, Colla et al. 2012). Based on the
above calculaons and trends, along with published reports of bumble bee decline and the assessors' best professional judgment,
we recommend this species for the Least Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus rufocinctus
Figure 2: Map used to measure range decline for Bombus rufocinctus
43

Species: Bombus sandersoni
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 98.83%
Persistence in current range relave to historic occupancy: 142.65%
Current relave abundance relave to historic values: 87.37%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): According to our analysis, this North American
species has not experienced serious declines in relave abundance,
persistence, or range in recent years. Specically, the average decline of 0% suggests a Least Concern category for this species. Col-
la et al. (2012) found no signicant changes in relave abundance of this species range-wide over the me periods examined, alt-
hough this study did ag B. sandersoni as of conservaon concern due to low persistence between 1991-2009 in historically occu-
pied areas. However, a large number of recent (2010-2012) records of this species range-wide have helped alleviate concerns
about the persistence of this species. Based on the above calculaons and trends, along with published reports of bumble bee de-
cline and the assessors' best professional judgment, we recommend this species for the Least Concern Red List category at this
me.
Figure 1: Relave abundance trends of Bombus sandersoni
Figure 2: Map used to measure range decline for Bombus sandersoni
44

Species: Bombus sitkensis
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 31.92%
Persistence in current range relave to historic occupancy: 89.46%
Current relave abundance relave to historic values: 76.08%
Average decline: 34.18%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): According to our analysis, this western North
American species has not experienced serious declines in relave
abundance or persistence in recent years. The apparent extent of occurrence (EOO) loss for this species is misleading, being largely
inuenced by a few widely scaered records from areas have been under-sampled in recent years. Therefore we are not relying
heavily on the EOO measure for this species in our assessment. Average decline in relave abundance and persistence (excluding
EOO) is 17.23%, suggesng a Least Concern Red List category. Based on the above calculaons and trends, along with published
reports of bumble bee decline and the assessors' best professional judgment, we recommend this species for the Least Concern
Red List category at this me.
Figure 1: Relave abundance trends of Bombus sitkensis
Figure 2: Map used to measure range decline for Bombus sitkensis
45

Species: Bombus suckleyi
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 42.61%
Persistence in current range relave to historic occupancy: 15.95%
Current relave abundance relave to historic values: 9.89%
Average decline: 77.18%
Preliminary IUCN Category: Crically Endangered; CR
IUCN Criteria: EN A2ce; CR A4be
Juscaon (Notes): According to our analysis, this western North
American species has experienced rapid declines in relave abun-
dance in recent years. The decade by decade relave abundance regression shows a gradual decline since the 1940s, and the rela-
ve abundance regression over just the past 50 years is highly signicant (R-squared value of nearly 1; showing a connued steep
decline). If we project the 50 year relave abundance regression into the future, it falls below the x-axis in the next 10 years. Nota-
bly, this species' regression mirrors that of B. occidentalis, a primary host. Both the past decline in relave abundance (90.11% over
the past 10 years) and predicted future decline in relave abundance (based on 50-year regression) jusfy a Crically Endangered
lisng, using criterion A2be + A3b. Note that the range and persistence of this species have also declined, however, since some his-
toric sites have not been re-sampled and since we only have records of this species in approximately six general localies for the
current me period, we were not comfortable using those measures of decline. Based on the above calculaons and trends, along
with published reports of bumble bee decline and the assessors' best professional judgment, we recommend this species for the
Crically Endangered Red List category at this me.
Figure 1: Relave abundance trends of Bombus suckleyi
Figure 2: Map used to measure range decline for Bombus suckleyi
46

Species: Bombus sylvicola
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 90.03%
Persistence in current range relave to historic occupancy: 82.86%
Current relave abundance relave to historic values: 96.41%
Average decline: 10.23%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): According to our analysis, this North American
species has not experienced serious declines in recent years. Speci-
cally, the average decline of 10.23% (based on relave abundance, persistence, and range) suggests that this species qualies for
the Least Concern category. Based on the above calculaons and trends, along with published reports of bumble bee decline and
the assessors' best professional judgment, we recommend this species for the Least Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus sylvicola
Figure 2: Map used to measure range decline for Bombus sylvicola
47

Species: Bombus ternarius
Assessment Level: Global
Status: Published
Current range size relave to historic range: 69.05%
Persistence in current range relave to historic occupancy: 103.61%
Current relave abundance relave to historic values: 162.21%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): According to our analysis, this North American
species has not experienced serious declines in relave abundance,
persistence, or range in recent years. This nding is consistent with other studies that have found this species to be relavely sta-
ble, both regionally and range-wide (e.g. Colla et al.2012, Colla and Packer 2008, Grix et al. 2009). Based on the above calculaons
and trends, along with published reports of bumble bee decline and the assessors' best professional judgment, we recommend this
species for the Least Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus ternarius
Figure 2: Map used to measure range decline for Bombus ternarius
48

Species: Bombus terricola
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 63.69%
Persistence in current range relave to historic occupancy: 67.32%
Current relave abundance relave to historic values: 19.17%
Average decline: 49.94%
Preliminary IUCN Category: Vulnerable; VU
IUCN Criteria: A2b
Juscaon (Notes): According to our analysis, this North American
species has declined over 30% in both range and persistence across
its enre range, with parcularly high (>80%) declines in relave abundance over the me period examined. Moreover, examina-
on of long-term trends reveals that the species' relave abundance in the current decade is lower than any other decade, and the
relave abundance change from the mean relave abundance has been greater than 66% in the past decade. Our metric that is
least sensive to variaon in collecon eort is persistence, and to a lesser degree relave abundance, and both of those metrics
suggest that this species should at least be classied as Vulnerable, if not Endangered. The average decline of 49.94% (including
relave abundance, persistence, and range) suggests a Vulnerable Red List Category. Based on the above calculaons and trends,
along with published reports of bumble bee decline and the assessors' best professional judgment, we recommend this species for
the Vulnerable Red List category at this me.
Figure 1: Relave abundance trends of Bombus terricola
Figure 2: Map used to measure range decline for Bombus terricola
49

Species: Bombus vagans
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 106.68%
Persistence in current range relave to historic occupancy: 103.69%
Current relave abundance relave to historic values: 108.97%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): According to our analysis, this widespread
North American species has not experienced serious declines in re-
cent years. Specically, the average decline of 0% (based on relave abundance, persistence, and range) suggests that this species
qualies for the Least Concern category. This nding is consistent with other studies that have found this species to be relavely
stable, range-wide (Colla et al. 2012). Based on the above calculaons and trends, along with published reports of bumble bee de-
cline and the assessors' best professional judgment, we recommend this species for the Least Concern Red List category at this
me.
Figure 1: Relave abundance trends of Bombus vagans
Figure 2: Map used to measure range decline for Bombus vagans
50

Species: Bombus vandykei
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 72.82%
Persistence in current range relave to historic occupancy: 59.99%
Current relave abundance relave to historic values: 163.71%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): This western North American species has ap-
parently declined in occupied area in southern California, although
range-wide, it is increasing in relave abundance, and the range and persistence declines are not large. The average decline of 0%
(based on relave abundance, persistence, and range) suggests that this species qualies for the Least Concern category. Based on
the above calculaons and trends, along with published reports of bumble bee decline and the assessors' best professional judg-
ment, we recommend this species for the Least Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus vandykei
Figure 2: Map used to measure range decline for Bombus vandykei
51

Species: Bombus variabilis
Assessment Level: Global
Status: Delayed for taxonomic status
Current range size relave to historic range: 56.77%
Persistence in current range relave to historic occupancy: 0.00%
Current relave abundance relave to historic values: 0.00%
Average decline: 81.08%
Preliminary IUCN Category: Crically Endangered; CR
IUCN Criteria: A2bc
Juscaon (Notes): This species is considered one of the rarest of
all North American bumble bee species, having been collected only a
few mes in the past twenty years, and not at all in the last decade (Williams et al. 2014 and supporng database). The decade by
decade relave abundance trend has been consistently downward since the 1920s, reaching zero in the recent decade (see Figure
1). This Psithyrus species uses B. pensylvanicus as a host; it historically occurred in the northern part of B. pensylvanicus' range,
which is where B. pensylvanicus has declined most severely. The species has exhibited 100% decline in relave abundance, EOO,
and persistence between the recent (2002-2012) and historic (1805-2001) me periods, poinng toward a Crically Endangered
Red List Category for this species in this region. In South and Central America, there are very few known records of this species
(Remy Vandame 2014, pers. comm.), and the status of this species is unclear. Based on the above calculaons and trends, along
with published reports of bumble bee decline and the assessors' best professional judgment, we recommend this species for the
Crically Endangered Red List category at this me.
Figure 1: Relave abundance trends of Bombus variabilis
Figure 2: Map used to measure range decline for Bombus variabilis
52

Species: Bombus vosnesenskii
Assessment Level: Global
Status: IUCN Accepted
Current range size relave to historic range: 89.30%
Persistence in current range relave to historic occupancy: 76.50%
Current relave abundance relave to historic values: 122.30%
Average decline: 0.00%
Preliminary IUCN Category: Least Concern; LC
IUCN Criteria:
Juscaon (Notes): Although this western North American species
has a modest range, it is oen by far the most common bumble bee
where it occurs, parcularly in urban and agricultural sengs (McFrederick and Lebuhn 2006, Rao and Stephen 2010). Like several
others in its subgenus, this species seems to be increasing in at least some parts of its range (NatureServe 2014), and also expand-
ing in range (Fraser et al. 2012). According to our analysis, this species has increased in relave abundance in recent years, and has
not declined signicantly in range or persistence. The average decline of 0% (based on relave abundance, persistence, and range)
suggests that this species qualies for the Least Concern Red List category. Based on the above calculaons and trends, along with
published reports of bumble bee decline and the assessors' best professional judgment, we recommend this species for the Least
Concern Red List category at this me.
Figure 1: Relave abundance trends of Bombus vosnesenskii
Figure 2: Map used to measure range decline for Bombus vosnesenskii
53

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