Western Monarch Population Plummets: Status, Probable Causes, and Recommended Conservation Actions

Abstract

Western monarch butterflies dropped by ~97% of their average historic abundance between the 1980s and mid-2010s. In winter 2018–2019, the population plummeted even farther, to fewer than 30,000 monarchs, which represents a single year drop of 86% and a drop of >99% since the 1980s. The population may now be hovering at its quasi-extinction threshold. In this Perspectives piece, we: (1) Place the current status in context, (2) Highlight the most likely window during the annual life cycle when the population declined, (3) Review probable causes of long-term declines, and (4) Recommend steps that the public, policy makers, and land managers can take to recover western monarchs. The available studies reinforce the hypotheses that overwintering habitat loss and loss of central California breeding habitat, as well as pesticide use, are likely important contributors to the western monarch's long-term decline. The most limiting part of the migratory cycle appears to be concentrated during the overwintering stage and/or in early spring. If western monarchs are in fact entering an extinction vortex, they need extraordinary efforts—focused on the most vulnerable periods of the annual cycle— to save the migration. Critical short-term conservation priorities are to (1) Protect, manage and restore overwintering habitat, (2) Protect monarchs and their habitat from pesticides, (3) Restore breeding and migratory habitat in California, (4) Protect, manage, and restore summer breeding and fall migration monarch habitat throughout the western monarch's range, and (5) Fill research gaps to inform western monarch recovery strategies.

Full text

PERSPECTIVE
published: 03 July 2019
doi: 10.3389/fevo.2019.00258
Frontiers in Ecology and Evolution | www.frontiersin.org 1July 2019 | Volume 7 | Article 258
Edited by:
Jay E. Diffendorfer,
United States Geological Survey,
United States
Reviewed by:
Tyler Flockhart,
University of Maryland Center for
Environmental Science (UMCES),
United States
Ralph Grundel,
U.S. Geological Survey, Great Lakes
Science Center, Chesterton, IN,
United States
*Correspondence:
Elizabeth E. Crone
elizabeth.crone@tufts.edu
Specialty section:
This article was submitted to
Conservation,
a section of the journal
Frontiers in Ecology and Evolution
Received: 05 March 2019
Accepted: 18 June 2019
Published: 03 July 2019
Citation:
Pelton EM, Schultz CB, Jepsen SJ,
Black SH and Crone EE (2019)
Western Monarch Population
Plummets: Status, Probable Causes,
and Recommended Conservation
Actions. Front. Ecol. Evol. 7:258.
doi: 10.3389/fevo.2019.00258
Western Monarch Population
Plummets: Status, Probable Causes,
and Recommended Conservation
Actions
Emma M. Pelton 1, Cheryl B. Schultz 2, Sarina J. Jepsen 1, Scott Hoffman Black 1and
Elizabeth E. Crone 3
*
1The Xerces Society for Invertebrate Conservation, Portland, OR, United States, 2Department of Biological Sciences,
Washington State University, Vancouver, WA, United States, 3Department of Biology, Tufts University, Medford,
MA, United States
Western monarch butterflies dropped by ∼97% of their average historic abundance
between the 1980s and mid-2010s. In winter 2018–2019, the population plummeted
even farther, to fewer than 30,000 monarchs, which represents a single year drop of
86% and a drop of >99% since the 1980s. The population may now be hovering
at its quasi-extinction threshold. In this Perspectives piece, we: (1) Place the current
status in context, (2) Highlight the most likely window during the annual life cycle when
the population declined, (3) Review probable causes of long-term declines, and (4)
Recommend steps that the public, policy makers, and land managers can take to recover
western monarchs. The available studies reinforce the hypotheses that overwintering
habitat loss and loss of central California breeding habitat, as well as pesticide use,
are likely important contributors to the western monarch’s long-term decline. The most
limiting part of the migratory cycle appears to be concentrated during the overwintering
stage and/or in early spring. If western monarchs are in fact entering an extinction
vortex, they need extraordinary efforts—focused on the most vulnerable periods of the
annual cycle— to save the migration. Critical short-term conservation priorities are to (1)
Protect, manage and restore overwintering habitat, (2) Protect monarchs and their habitat
from pesticides, (3) Restore breeding and migratory habitat in California, (4) Protect,
manage, and restore summer breeding and fall migration monarch habitat throughout
the western monarch’s range, and (5) Fill research gaps to inform western monarch
recovery strategies.
Keywords: Danaus plexippus plexippus, western monarchs, quasi-extinction, conservation, population trends
INTRODUCTION
Monarch butterflies (Danaus plexippus plexippus) across North America have been undergoing
a multi-decade decline (Semmens et al., 2016; Schultz et al., 2017). Nonetheless, the crash
of the western population (Figure 1) in winter 2018–2019 was particularly stunning. In
2017, we estimated that the overwintering population had dropped by 97% of its average
historic abundance, from ∼3 to 10 million to ∼200–300 thousand butterflies (Schultz et al.,
2017). In winter 2018-2019, the population plummeted to fewer than 30,000 monarchs,

Pelton et al. Western Monarch Population Plummets
FIGURE 1 | Western monarchs breed west of the Rocky mountains
and primarily overwinter at over 200 sites (black points) along the Pacific coast
in California. During the spring, monarchs leave the overwintering habitat
(colored blue) to disperse (orange arrows) across the West. The butterflies
breed continuously across the West during the summer (colored white); in the
fall, they return (blue arrows) to the overwintering grounds. [Tag recoveries in
Mexico show that at least some western monarchs migrate to central Mexico,
mixing with the eastern monarch overwintering population; whether or not
monarchs from Mexico return to the West in the spring has not been
documented, but is suspected (dashed orange arrow)]. The authors have
monitored monarch breeding phenology and milkweed at 12 sites throughout
the West (orange points) as part of a multi-year study.
which represents a single year drop of 86%, and a >99% drop
since the 1980s (Figure 2A).
In this Perspective, we: (1) Place the current status in
context, both how trends compare to the eastern population
and potential implications of dropping to unprecedentedly low
abundance in the West, (2) Highlight the most likely window
during the annual life cycle when the population declined,
(3) Review probable causes of long-term declines, and (4)
Use our understanding of drivers of declines to recommend
steps that the public, policy makers, and land managers can
take including identifying knowledge gaps for which focused
mechanistic studies could contribute to developing more effective
and efficient conservation actions.
STATUS OF WESTERN MONARCHS IN
WINTER 2018–2019
Since 1997, volunteers have estimated the overwintering
population in California each fall at coastal groves (Xerces Society
Western Monarch Thanksgiving Count, 2019). The 2018 Xerces
Thanksgiving Count revealed a new low—only 28,429 monarchs
were tallied—<1% of the historic population (Figure 2A). The
current trend in western monarchs is in contrast to eastern
monarchs, which hit the highest estimated population size in
the last decade in winter 2018–2019 with 6.05 hectares occupied
(Rendón-Salinas et al., 2019).
We know from our past analyses that a western population
of <30,000 butterflies is unprecedented. The 2018 Thanksgiving
count mirrors a textbook extinction vortex (Gilpin and Soule,
1986), in the sense that fluctuations in abundance—which have
been happening throughout the past 30 years—become riskier as
the population becomes smaller. As populations become smaller,
“ordinary” environmental variation can cause a population to
drop below a point from which extinction is inevitable, unless
extraordinary measures are taken. We call this point the quasi-
extinction threshold. In 2016, a group of experts proposed
30,000 butterflies as the quasi-extinction threshold for western
monarchs (Schultz et al., 2017). Now, it is suddenly imperative to
know if the experts were correct, and, if so, what extraordinary
measures need to be taken to preserve the population.
In general, we know very little about what happens when
formerly large populations become small. Individuals in small
populations may have reduced mating success, suffer increased
predation, and lose other benefits of schooling or flocking
(Courchamp et al., 1999). These effects due to small population
size are known as “Allee effects” and are difficult to estimate
in wild populations because they are only expressed after a
population has begun to decline to extinction (Liermann and
Hilborn, 1997). Therefore, setting quasi-extinction thresholds
is one of the most subjective steps of population viability
analysis (e.g., Frick et al., 2010; McGowan et al., 2017). If the
published quasi-extinction threshold is correct, then positive
density-dependent processes associated with Allee effects could
lead to further rapid decline. If the quasi-extinction threshold is
incorrect, we will see the western monarch recover to a larger
population size. Regardless, this serves as a call to intensify efforts
to boost abundance to healthy enough numbers in the wild for
the population to be able to sustain itself through normal ups and
downs in the population size.
ENVIRONMENTAL DRIVERS
Causes of Rapid Decline From 2017 to 2018
Given the large drop in western monarchs from 2017 to 2018,
some are tempted to blame the weather for the low numbers.
Late rainy season storms swept across California in March. There
was a severe and extended wildfire season in the West and smoke
was widespread at times. California is still recovering from a
historic drought. Large amplitude inter-annual fluctuations are
an intrinsic aspect of butterfly population dynamics, and causes
of year-to-year variation are not necessarily the same as the
causes of long-term declines. Nonetheless, it is important to try
to understand western monarch abundance throughout the year
from winter 2017–2018 through winter 2018–2019, when the
decline occurred.
Starting in winter 2016–2017, the Xerces Society and
volunteers began a second count at overwintering sites, the New
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Pelton et al. Western Monarch Population Plummets
FIGURE 2 | Western monarch abundance at (A) overwintering and (B) breeding sites. In both panels, shaded areas show 95% confidence limits. (A) Western
monarch butterfly 1981–2018 estimates for overwintering abundance during the Thanksgiving Count time period in coastal California. Estimates for 1981–2017 were
calculated with state space models (Schultz et al., 2017), scaled to be comparable to the raw count from 2018 (shown). (B) Monarch egg and larva counts per stem
at all 12 monitoring sites (shown in Figure 1) throughout the season in 2017 and 2018. Curves were fitted with generalized additive models (Wood, 2011) to show
general trends in abundance. The fact that the two curves are parallel suggests that densities were lower by the time monarchs arrived in 2018; the decline does not
appear to be due to different dynamics during breeding. Note the log scale and 10-fold difference among years.
Year’s count (centered around New Year’s Day, to complement
the Thanksgiving Count 6 weeks earlier). Monarch abundance at
the New Year’s Count had declined by 43% on average in 2017
(n=44 sites), 49% on average in 2018, (n=115 sites) and 36%
in 2019 (n=130 sites), when compared to monarch abundance
at those same sites during the Thanksgiving Count. These data
suggest that monarch butterflies did not have exceptionally low
survival between November 2017 and January 2018, compared to
the previous year.
In addition to counts at overwintering sites, we started
monitoring summer breeding of western monarchs in 2017 at
12 sites throughout the West (Figure 1). Across these 2 years,
the density of monarch eggs and larvae was consistently lower in
2018 than 2017 (Figure 2B), with about a 10-fold decline between
the 2 years (average immature monarchs/stem =0.0273 [95% CI
=0.0025, 0.2953] in 2017 and 0.0022 [95% CI =0.0001, 0.0429]
in 2018; paired t-test of site averages between years: t= −2.53, df
=10, P=0.030). We therefore suggest that the drop measured
at Thanksgiving 2018 originated before the beginning of the 2018
breeding season, either late during the overwintering season or
very early in the breeding season.
This inference is consistent with Espeset et al. (2016) who
concluded that western monarch declines were concentrated in
early spring. Of the environmental events that seemed “unusual”
in 2017–2018, this pattern points to the possible negative effects
of unusually heavy rains in March 2018 with the caveat that many
other factors may have caused the population drop, including the
interaction of weather with habitat quality at overwintering sites,
and habitat inland from the coast in California, where the first
generation breeds.
Causes of Long-Term Declines
In the larger eastern population, declines have largely been
attributed to overwintering habitat loss (Brower et al., 2012;
Vidal et al., 2013) and breeding habitat loss, especially through
the use of herbicides (e.g., Pleasants and Oberhauser, 2012;
Flockhart et al., 2014). We (Crone et al., in press) recently
evaluated climate and land use factors simultaneously as potential
drivers of western monarch abundance. Trends in abundance
were more strongly associated with land use variables including
coastal development in overwintering areas and pesticide use
(glyphosate and neonicotinoid insecticides) in breeding areas
than climate variables in both overwintering and breeding areas
(Crone et al., in press). These results are consistent with the
hypotheses that overwintering habitat loss and loss of central
California breeding habitat are important for western monarchs
(see Espeset et al., 2016) and that trends in pesticide use likely
contribute to declining monarch populations as well as declines
in other butterfly taxa (see also Forister et al., 2016).
In addition to this broad scale analysis, we estimated
daily survival using data from Tuskes and Brower (1978),
for comparison with population declines estimated from
Thanksgiving and New Year’s counts. Daily survival at Natural
Bridges near Santa Cruz was 0.995 (95% CI 0.988, 0.997) and
at Santa Barbara was 0.991 (0.989, 0.993). Over 6 weeks (the
approximate time between Thanksgiving to New Year’s counts),
this historical estimate translates into a 29% drop (95% CI
12–40%) using estimates from Santa Cruz and a 32% drop
(95% CI 26–37%) using estimates from Santa Barbara. Hence,
based on the best available evidence, apparent survival during
winter in recent years (36–49% drop) has been lower than
it was in the past. This change reinforces the importance of
overwintering habitat quality on the long-term decline of the
western monarch population. At the present time, we have not
found comparable data to evaluate whether breeding season
survival or reproduction have changed in western monarchs.
URGENT STEPS FOR CONSERVATION
To date, western monarchs have received far less conservation
attention and financial resources than the larger eastern
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Pelton et al. Western Monarch Population Plummets
population. Nonetheless, the western monarch breeds
across most of the US west of the Rocky Mountains,
a significant portion of the monarch’s overall North
American range. It makes an important contribution to the
resilience, redundancy, and representation of the species as a
whole (see definition in Shaffer and Stein, 2000).
While the precise causes of the recent dramatic drop in
the western population, as well as the longer term decline,
remain unknown, this knowledge gap should not prevent
conservation action. We suggest that a precautionary approach
be taken to remediate potential causes of decline. Specifically
we recommend efforts (1) to protect, enhance, and actively
manage overwintering sites; (2) to protect monarch habitat
from pesticides, particularly systemic insecticides (including
neonicotinoids); (3) to supplement larval and adult resources-
especially in the early spring-in California; (4) to identify, protect,
and enhance monarch habitats throughout the West, and (5)
to prioritize research efforts to answer questions critical to
developing an effective and efficient recovery strategy. Here, we
briefly explain our recommendations, and their relationship to
the causes of western monarch declines, described above. These
recommendations and relevant resources are expanded in in our
“Western Monarch Call to Action.”1
Protect, Manage, and Restore
Overwintering Habitat
Our analyses (“Environmental drivers” above) point to the
importance of monarch habitat in winter and early spring,
prior to the breeding season. Conservation biologists have long
known that efforts focused only on one stage of a species’ life
cycle (e.g., breeding) may not be sufficient if populations are
limited by another life stage [e.g., overwintering (Brown et al.,
2017)]. Despite the importance of monarchs to Californians
and the state’s tourism economy, few overwintering sites
are meaningfully protected (International Environmental Law
Project and the Xerces Society, 2012) and sites continue to be
destroyed—indeed, from 2017 to present, over one dozen sites
have either been newly destroyed or are reported to be threatened
by inappropriate tree trimming, removal, and/or development
(Xerces Society Western Monarch Overwintering Sites Database
2019, unpublished). To protect remaining habitat, overwintering
sites could be designated as Environmentally Sensitive Habitat
Areas (ESHAs) by the California Coastal Commission, protected
as Critical Habitat if monarchs were listed under the federal
Endangered Species Act, protected by California Department of
Fish and Wildlife if monarchs were listed as endangered under
the California Endangered Species Act, or a new law could be
created by the California state legislature to protect overwintering
sites from destruction.
To address the need for active management of overwintering
sites, the majority of which occur on publicly owned land, a
greater financial investment is needed. The Monarch Butterfly
and Pollinator Rescue Program (California Assembly Bill 2421),
was signed into law in 2018, and $3 million was allocated to this
program. An additional $3.9 million was recently allocated for
1www.savewesternmonarchs.org
restoration of overwintering sites owned by the City of Goleta.
While these represent important steps forward, more resources
are needed to restore and manage the over 200 actively used
overwintering sites. While there are no published estimates,
restoring a significant number of overwintering sites would easily
require tens of millions of dollars and, more importantly, would
benefit from sustained funding to continue to manage the groves
for monarchs in the long-term. Of the Top 50 priority sites
identified by Pelton et al. (2016) many of the most important
sites are owned by the California Department of Parks and
Recreation, followed by cities, U. S. Department of Defense,
East Bay Regional Parks District, and county, university, and
other state and federal agencies as well as private entities. Some
of these owners do not encourage or permit the planting of
eucalyptus (the dominant tree used by monarchs in California
during overwintering), nor are these land managers necessarily
focused on managing for monarch overwintering habitat—and,
in some cases, may be unaware of the full extent of overwintering
habitat within their jurisdiction.
Protect Monarchs and Their Habitat From
Pesticides
In our analyses of long-term trends, insecticide and herbicide
use were almost as tightly associated with monarch declines as
overwinter habitat loss. Restricting insecticide and herbicide use
increases adult Lepidoptera abundance (Frampton and Dorne,
2007). Broadcast herbicide use can kill host and nectar plants
and have non-target effects on butterflies (Stark et al., 2012).
We advise protecting the most important monarch breeding
and overwintering habitats from insecticide and herbicide use.
Specifically, we recommend avoiding herbicide applications
that damage monarch breeding and migratory habitat such as
milkweed and wildflowers. These recommendations apply to
home gardens and lawns, as well as lands used for agriculture and
other purposes. If herbicides are used, we advise using targeted
application methods, avoiding large-scale broadcast applications
of herbicides, and taking precautions to limit off-site movement
of herbicides. Neonicotinoid insecticides, in particular, should be
avoided at all times in monarch habitat due to their persistence,
systemic nature, and toxicity. When purchasing milkweeds
or wildflowers from nurseries, we recommend ensuring that
they have not been treated with neonicotinoids or other
systemic insecticides.
Restore Breeding and Migratory Habitat in
California
Enhancing monarch breeding habitat may be able to partly
mitigate reductions in overwintering habitat quality because
larger populations at the end of the summer can potentially
withstand higher mortality. Numerous studies have quantified
the importance of host and nectar plants for butterfly populations
(Dennis et al., 2006; Dennis, 2010), and restoration efforts
which enhance host and nectar have been effective approaches
for the conservation of rare butterflies (Carleton and Schultz,
2013). We recommend planting native milkweeds in areas
where they historically grew in California, and, in particular,
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Pelton et al. Western Monarch Population Plummets
in the Coast Range, Central Valley, and the foothills of the
Sierra Nevada, areas where the first generation of monarchs are
produced each spring. Early emerging native species that may
be particularly important in spring include woollypod (Asclepias
eriocarpa), California (A. californica), and heartleaf milkweed
(A. cordifolia). However, commercial availability of these species
is limited. Later-emerging native California milkweed species
that are more readily available, and may also help, include
narrowleaf (A. fascicularis) and showy milkweed (A. speciosa).
In the desert southwest of California, we recommend rush
(A. subulata) and desert milkweed (A. erosa). We recommend
only planting milkweed >5 miles inland from overwintering
sites, as milkweed does not naturally grow close to the
coast north of Santa Barbara and milkweed at overwintering
sites can interrupt natural overwintering behavior. Tropical
milkweed (A. curassavica) is exotic to California, disrupts the
monarch’s migratory cycle, and serves as a reservoir for monarch
pathogens (Satterfield et al., 2016). As such we recommend
against planting tropical milkweed. In places where tropical
milkweed already exists, we recommend cutting it back to
the ground in the fall (October/November) and repeatedly
throughout the winter to mimic native milkweed phenology
and break the disease cycle; ideally, it should be replaced by
native milkweed.
In addition, we recommend planting nectar-rich wildflowers,
especially those that bloom early in the spring (February–April)
and fall (September-October). If located close to the coast,
plants which bloom in the winter (November-January) may also
be useful.
Protect, Manage, and Restore Summer
Breeding and Fall Migration Monarch
Habitat Throughout the Western Monarch’s
Range
Identifying key areas of breeding and migrating habitat for
monarchs in the West remains a knowledge gap. Some
geographic regions contribute disproportionately to the eastern
monarch overwintering population in Mexico (e.g., Flockhart
et al., 2017), and it is important to know whether the same
is true for western monarchs. No data exist from which we
could meaningfully evaluate their importance for short- or
long-term population declines. Thus, while some of the most
important monarch habitat within its western breeding (Yang
et al., 2016; Dilts et al., 2019) and overwintering (Pelton
et al., 2016) range has already been identified, additional work
is needed to identify and rank these areas. We recommend
identifying existing monarch habitat, ensuring that it is managed
to protect monarchs (Xerces Society, 2018) and in some regions
and landscape types, we recommend habitat enhancement
or restoration. Habitat restoration in regions where monarch
habitat historically occurred, but have likely been lost (such
as the Columbia Plateau and Snake River Plain), as well as
riparian areas, are high priority areas outside of California.
Such restoration would likely benefit from habitat elements
beyond milkweed and nectar, such as shrubs or trees for roosting
and shade.
Fill Research Gaps to Inform Western
Monarch Recovery Strategies
Breeding and migrating habitat are only a few of the gaps
in our knowledge of western monarchs. We especially need
observations of monarch biology in places where human
populations are low (e.g., the Great Basin desert) and at times
of year when monarch butterflies are sparse (e.g., early spring
in western California, just as they leave the overwintering
grounds). We urge volunteers across the West to collect
observations of monarchs and milkweeds, especially in the early
spring (February–April), the period in which monarchs typically
leave the overwintering sites. Together these observations will
help answer questions about monarch breeding phenology.
In this year, when numbers are low in the West and high
in the East, targeted observations of monarch adults and
larvae may also tell us whether the West sees an influx of
monarchs arriving from Mexico (see Pyle, 2015). Monarch
adult, larva, egg, nectaring, and milkweed sightings can be
reported to the Western Monarch Milkweed Mapper2and
first adults observed can be reported to Journey North3
as well. More robust monitoring may be achieved through
increased western participation in the Integrated Monarch
Monitoring Program4.
We urge academic ecologists to conduct targeted
experimental and observational studies to complement
large-scale observations like the ones described above. In
both the eastern and western monarch populations, filling
knowledge gaps about demography throughout the life cycle
would allow us to design quantitative thresholds for conservation
and restoration. For example, it may be possible for targeted
actions at one point in the life cycle to make up for stresses
at other points. If climate change is making the landscape less
favorable, can we make up for this with improved breeding
or overwintering habitat quality and/or area? Can more
breeding habitat in the outer parts of the breeding distribution
make up for habitat loss at breeding or overwintering sites
in California? Intuitively, the answer is probably “yes, but
only partly.” To answer this in a more quantitative way,
we need a better understanding of how the life cycle pieces
fit together.
CONCLUSION
In closing, western monarchs are currently in peril. Their status
reflects a long-term decline due to some combination of habitat
loss and degradation in their overwintering and breeding range,
increased pesticide use, and possibly climate change. The recent
dramatic drop reflects conditions when the least is known about
western monarchs—where they are, what habitat they are using,
and what they need to survive, migrate and reproduce. In spite of
their current status, monarchs are resilient; we believe that rapid
conservation actions can recover the population. This recovery
will require the protection of monarchs and their habitat, as well
as targeted research to understand the unique life cycle of western
2www.monarchmilkweedmapper.org
3https://journeynorth.org/monarchs
4https://monarchjointventure.org/immp
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Pelton et al. Western Monarch Population Plummets
monarch butterflies. If we are going to take these actions, the time
is now.
DATA AVAILABILITY
The datasets for this study will not be made publicly
available because restrictions apply to some of the
datasets. Some of the datasets are in a publicly
accessible repository:
The Xerces Society Western Monarch Thanksgiving and New
Year’s Counts analyzed in this study can be found at www.
westernmonarchcount.org/data.
Restrictions apply to some of the datasets:
The Xerces Society Western Monarch Overwintering
Sites Database 2019 is not publicly available because
of privacy concerns with a subset of the information.
Requests to access the database should be directed to Emma
Pelton, monarchs@xerces.org.
The western monarch and milkweed phenology dataset
summarized in this manuscript are not publicly available because
it is part of a study currently in-progress. Requests to access the
datasets should be directed to Cheryl Schultz, schultzc@wsu.edu.
AUTHOR CONTRIBUTIONS
EP, SJ, and SB (along with others—see Acknowledgments)
oversee Thanksgiving and New Year’s Counts and maintain the
overwintering sites database. All authors contributed to funding
and implementing the 2017–2018 surveys in the breeding range.
EC conceived and ran all analyses with input from CS and EP. All
authors wrote and revised the manuscript.
FUNDING
Funds for the 2017–2018 breeding and phenology surveys
and analysis were provided by Department of Defense Legacy
Natural Resources Program (NR 16 Western Monarch) and the
U.S. Fish & Wildlife Service Coastal Program. Authors were
supported by their institutions (WSU, Tufts and Xerces Society)
and EC, SJ, EP, and CS were partly supported by the National
Science Foundation (NSF DEB 1920834).
ACKNOWLEDGMENTS
Thank you to the Western Monarch Thanksgiving Count
volunteers, particularly our regional coordinators, Mia Monroe,
and Katie Hietala-Henschell of the Xerces Society; Stephanie
McKnight of the Xerces Society and Cameron Thomas of
Washington State University for conducting the fieldwork
for the breeding and milkweed phenology project; fellow
western monarch researchers and conservation practitioners
for conversations that led to the development to the Western
Monarch Call to Action; US Fish and Wildlife Service Coastal
Program, Department of Defense, National Science Foundation,
and Xerces Society members and other funders for supporting the
work presented in this Perspective.
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Conflict of Interest Statement: The authors declare that the research was
conducted in the absence of any commercial or financial relationships that could
be construed as a potential conflict of interest.
Copyright © 2019 Pelton, Schultz, Jepsen, Black and Crone. This is an open-access
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