Monarch Conservation Science Partnership

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The Monarch Conservation Science Partnership is a USGS led group of scientists, managers, and conservation organizations who perform science related to the conservation of monarch butterflies. We come from federal agencies, non profits, and academia and from the three countries where monarchs range (Mexico, Canada, and the United States). To date meetings of the MCSP have been hosted by the USGS John Wesley Powell Center for Analysis and Synthesis in Ft. Collins, CO. PIs include Darius Semmens and Jay Diffendorfer (GECSC) and Wayne Thogmartin (UMESC).

Are we witnessing the end of the migration of monarchs in the eastern U.S.?
What is the issue?

The Eastern, migratory population of monarch butterflies has declined by ~80% over the last decade, despite efforts in Mexico to end illegal logging in the fir forests used by overwintering monarchs. These declines are coincident with the rapid adoption of glyphosate-resistant crops on agricultural lands of the north central U.S.

What are the challenges?

The monarch’s multi-generational migration between overwintering grounds in central Mexico and summer breeding grounds in northern U.S. and southern Canada creates shared management responsibilities across North America.

No national-level monitoring and insufficient basic ecological research (e.g., few habitat-specific estimates of milkweed density) lead to key gaps in our understanding of monarch life history and ecology.

Threats are numerous, including herbicide and pesticide application, loss of natural and conserved areas, and disruption from climate change and consequences of extreme weather, leading to ‘death by a thousand cuts’.

Strategies for mitigating threats are weakly defined.

The Partnership is engaged in considerable research to address information gaps associated with the ecology and conservation of monarch butterflies. Among these efforts include analyses of extinction risk, continental-scale full-annual-cycle demography, threats assessment, overwinter density estimation, milkweed target estimation, and storylines for conservation recovery. Strategies for sampling monarchs and the milkweed that sustains them are being developed. In addition, geospatial tools, both desktop and online, for aiding in conservation planning have been completed.

Decline in the eastern migratory monarch butterfly population as surveyed by the World Wildlife Fund-Mexico

Decline in the eastern migratory monarch butterfly population as surveyed by the World Wildlife Fund-Mexico.Populations in the high-elevation Oyamel fir forests where eastern monarchs overwinter are indexed by the area over which they occur.Semmens et al. (2016) provided an adjusted measurement of population size which corrects for observation error.(Public domain.)


Quasi-extinction risk and population targets for the Eastern, migratory population of monarch butterflies (Danaus plexippus)

The Eastern, migratory population of monarch butterflies (Danaus plexippus), an iconic North American insect, has declined by ~80% over the last decade. The monarch’s multi-generational migration between overwintering grounds in central Mexico and the summer breeding grounds in the northern U.S. and southern Canada is celebrated in all three countries and creates shared management responsibilities across North America. Here we present a novel Bayesian multivariate auto-regressive state-space model to assess quasi-extinction risk and aid in the establishment of a target population size for monarch conservation planning. We find that, given a range of plausible quasi-extinction thresholds, the population has a substantial probability of quasi-extinction, from 11–57% over 20 years, although uncertainty in these estimates is large. Exceptionally high population stochasticity, declining numbers, and a small current population size act in concert to drive this risk. An approximately 5-fold increase of the monarch population size (relative to the winter of 2014–15) is necessary to halve the current risk of quasi-extinction across all thresholds considered. Conserving the monarch migration thus requires active management to reverse population declines, and the establishment of an ambitious target population size goal to buffer against future environmentally driven variability.

Density estimates of monarch butterflies overwintering in central Mexico

Given the rapid population decline and recent petition for listing of the monarch butterfly (Danaus plexippus L.) under the Endangered Species Act, an accurate estimate of the Eastern, migratory population size is needed. Because of difficulty in counting individual monarchs, the number of hectares occupied by monarchs in the overwintering area is commonly used as a proxy for population size, which is then multiplied by the density of individuals per hectare to estimate population size. There is, however, considerable variation in published estimates of overwintering density, ranging from 6.9–60.9 million ha−1. We develop a probability distribution for overwinter density of monarch butterflies from six published density estimates. The mean density among the mixture of the six published estimates was ∼27.9 million butterflies ha−1 (95% CI [2.4–80.7] million ha−1); the mixture distribution is approximately log-normal, and as such is better represented by the median (21.1 million butterflies ha−1). Based upon assumptions regarding the number of milkweed needed to support monarchs, the amount of milkweed (Asclepias spp.) lost (0.86 billion stems) in the northern US plus the amount of milkweed remaining (1.34 billion stems), we estimate >1.8 billion stems is needed to return monarchs to an average population size of 6 ha. Considerable uncertainty exists in this required amount of milkweed because of the considerable uncertainty occurring in overwinter density estimates. Nevertheless, the estimate is on the same order as other published estimates. The studies included in our synthesis differ substantially by year, location, method, and measures of precision. A better understanding of the factors influencing overwintering density across space and time would be valuable for increasing the precision of conservation recommendations.

National Valuation of Monarch Butterflies Indicates an Untapped Potential for Incentive-Based Conservation

The annual migration of monarch butterflies (Danaus plexippus) has high cultural value and recent surveys indicate monarch populations are declining. Protecting migratory species is complex because they cross international borders and depend on multiple regions. Understanding how much, and where, humans place value on migratory species can facilitate market-based conservation approaches. We performed a contingent valuation study of monarchs to understand the potential for such approaches to fund monarch conservation. The survey asked U.S. respondents about the money they would spend, or have spent, growing monarch-friendly plants, and the amount they would donate to monarch conservation organizations. Combining planting payments and donations, the survey indicated U.S. households valued monarchs as a total one-time payment of $4.78–$6.64 billion, levels similar to many endangered vertebrate species. The financial contribution of even a small percentage of households through purchases or donations could generate new funding for monarch conservation through market-based approaches.

A trans-national monarch butterfly population model and implications for regional conservation priorities

The monarch has undergone considerable population declines over the past decade, and the governments of Mexico, Canada, and the United States have agreed to work together to conserve the species. Given limited resources, understanding where to focus conservation action is key for widespread species like monarchs. To support planning for continental-scale monarch habitat restoration, the authors addressed the question of where restoration efforts are likely to have the largest impacts on monarch butterfly population growth rates. They did so by developing a spatially explicit trans-national model of the monarch butterfly's multi-generational life cycle. The authors reported that improving monarch habitat in the north central or southern parts of the monarch range yields a slightly greater increase in the population growth rate than restoration in other regions. However, combining restoration efforts across multiple regions yields population growth rates above replacement with smaller simulated improvements in habitat per region than single-region strategies. These findings suggest that conservation investment in projects across the full monarch range will be more effective than focusing on one or a few regions, and will require international cooperation across many land use categories.


Monarch Conservation Science Partnership

(Public domain.)

Monarch Conservation Science Partnership Map Viewer and Tools

 County Ranking Tool

MCSP County Ranking Tool

The County Ranking Tool gives users the ability to prioritize counties within the conterminous United States according to multiple input field criteria important for monarch butterfly conservation. A spatial data layer representing U.S. counties was assembled and attributed with the information for each input criteria. Some of these criteria represent positive attributes for monarch butterfly conservation while others quantify potential threats. (Public domain.)

Monarch Conservation Science Partnership Map Viewer and Tools 

Milkweed Calculator Tools

MCSP Milkweed Calculator Tools

Two separate milkweed calculator tools were developed to allow users the ability to model the anticipated number of milkweeds on the landscape. The tools use a county summary shapefile (attribute table) as a base layer for analysis. A seamless milkweed habitat raster was used as the source for the summary information contained within this shapefile. (Public domain.)

Monarch Conservation Science Partnership Map Viewer and Tools

County Area Adjustment Tool

MCSP County Area Adjustment Tool

A separate tool was developed to allow users the ability to make hypothetical adjustments to the area (in hectares or acres) of milkweed habitat classes for a user-defined set of counties. The results of these hypothetical changes can then be used as input in the milkweed calculator tools and can help to inform the user on the impact of specific conservation development activities. (Public domain.)

Thogmartin, W. E., L. López-Hoffman, J. Rohweder, J. Diffendorfer, R. Drum, D. Semmens, S. Black, I. Caldwell, D. Cotter, P. Drobney, L. L. Jackson, M. Gale, D. Helmers, S. Hilburger, E. Howard, K. Oberhauser, J. Pleasants, B. Semmens, O. Taylor, P. Ward, J. Weltzin, and R. Wiederholt. 2017. Restoring monarch butterfly habitat in the Midwestern U.S.: “All Hands on Deck”. Environmental Research Letters 12:074005.  

DOI: 10.1088/1748-9326/aa7637

The eastern migratory population of monarch butterflies (Danaus plexippus plexippus) has declined by >80% within the last two decades. One possible cause of this decline is the loss of ≥1.3 billion stems of milkweed (Asclepias spp.), which monarchs require for reproduction. In an effort to restore monarchs to a population goal established by the US Fish and Wildlife Service and adopted by Mexico, Canada, and the US, we developed scenarios for amending the Midwestern US landscape with milkweed. Scenarios for milkweed restoration were developed for protected area grasslands, Conservation Reserve Program land, powerline, rail and roadside rights of way, urban/suburban lands, and land in agricultural production. Agricultural land was further divided into productive and marginal cropland. We elicited expert opinion as to the biological potential (in stems per acre) for lands in these individual sectors to support milkweed restoration and the likely adoption (probability) of management practices necessary for affecting restoration. Sixteen of 218 scenarios we developed for restoring milkweed to the Midwestern US were at levels (>1.3 billion new stems) necessary to reach the monarch population goal. One of these scenarios would convert all marginal agriculture to conserved status. The other 15 scenarios converted half of marginal agriculture (730 million stems), with remaining stems contributed by other societal sectors. Scenarios without substantive agricultural participation were insufficient for attaining the population goal. Agricultural lands are essential to reaching restoration targets because they occupy 77% of all potential monarch habitat. Barring fundamental changes to policy, innovative application of economic tools such as habitat exchanges may provide sufficient resources to tip the balance of the agro-ecological landscape toward a setting conducive to both robust agricultural production and reduced imperilment of the migratory monarch butterfly.

Thogmartin, W. E., R. Wiederholt, K. Oberhauser, R. G. Drum, J. E. Diffendorfer, S. Altizer, O. R. Taylor, J. Pleasants, D. Semmens, B. X. Semmens, R. Erickson, K. Libby, and L. López-Hoffman. 2017. Monarch butterfly population decline in North America: identifying the threatening processes. Royal Society Open Science 4:170760.  DOI: 10.1098/rsos.170760   

The monarch butterfly (Danaus plexippus) population in North America has sharply declined over the last two decades. Despite rising concern over the monarch butterfly’s status, no comprehensive study of the factors driving this decline has been conducted. Using partial least-squares regressions and time-series analysis, we investigated climatic and habitatrelated factors influencing monarch population size from 1993 to 2014. Potential threats included climatic factors, habitat loss (milkweed and overwinter forest), disease and agricultural insecticide use (neonicotinoids). While climatic factors, principally breeding season temperature, were important determinants of annual variation in abundance, our results indicated strong negative relationships between population size and habitat loss variables, principally glyphosate use, but also weaker negative effects from the loss of overwinter forest and breeding season use of neonicotinoids. Further declines in population size because of glyphosate application are not expected. Thus, if remaining threats to habitat are mitigated we expect climate-induced stochastic variation of the eastern migratory population of monarch butterfly around a relatively stationary population size.

Pleasants, J. M., M. P. Zalucki, K. S. Oberhauser, L. P. Brower, O. R. Taylor, and W. E. Thogmartin. 2017. Interpreting surveys to estimate the size of the monarch butterfly population: pitfalls and prospects. PLoS ONE 12(7): e0181245.  DOI: 10.1371/journal.pone.0181245

To assess the change in the size of the eastern North American monarch butterfly summer population, studies have used long-term data sets of counts of adult butterflies or eggs per milkweed stem. Despite the observed decline in the monarch population as measured at overwintering sites in Mexico, these studies found no decline in summer counts in the Midwest, the core of the summer breeding range, leading to a suggestion that the cause of the monarch population decline is not the loss of Midwest agricultural milkweeds but increased mortality during the fall migration. Using these counts to estimate population size, however, does not account for the shift of monarch activity from agricultural fields to non-agricultural sites over the past 20 years, as a result of the loss of agricultural milkweeds due to the near ubiquitous use of glyphosate herbicides. We present the counter-hypotheses that the proportion of the monarch population present in non-agricultural habitats, where counts are made, has increased and that counts reflect both population size and the proportion of the population observed. We use data on the historical change in the proportion of milkweeds, and thus monarch activity, in agricultural fields and non-agricultural habitats to show why using counts can produce misleading conclusions about population size. We then separate out the shifting proportion effect from the counts to estimate the population size and show that these corrected summer monarch counts show a decline over time and are correlated with the size of the overwintering population. In addition, we present evidence against the hypothesis of increased mortality during migration. The milkweed limitation hypothesis for monarch decline remains supported and conservation efforts focusing on adding milkweeds to the landscape in the summer breeding region have a sound scientific basis.

​Saunders, S. P., L. Ries, K. S. Oberhauser, W. E. Thogmartin, and E. F. Zipkin. 2018. Local and cross-seasonal effects of climate and land-use on breeding abundances of a migratory species. Ecography

​DOI: ​10.1111/ecog.02719 

Quantifying how climate and land use factors drive population dynamics at regional scales is complex because it depends on the extent of spatial and temporal synchrony among local populations, and the integration of population processes throughout a species’ annual cycle. We modeled weekly, site-specific summer abundance (1994–2013) of monarch butterflies Danaus plexippus at sites across Illinois, USA to assess relative associations of monarch abundance with climate and land use variables during the winter, spring, and summer stages of their annual cycle. We developed negative binomial regression models to estimate monarch abundance during recruitment in Illinois as a function of local climate, site-specific crop cover, and county-level herbicide (glyphosate) application. We also incorporated cross-seasonal covariates, including annual abundance of wintering monarchs in Mexico and climate conditions during spring migration and breeding in Texas, USA. We provide the first empirical evidence of a negative association between county-level glyphosate application and local abundance of adult monarchs, particularly in areas of concentrated agriculture. However, this association was only evident during the initial years of the adoption of herbicide-resistant crops (1994–2003). We also found that wetter and, to a lesser degree, cooler springs in Texas were associated with higher summer abundances in Illinois, as were relatively cool local summer temperatures in Illinois. Site-specific abundance of monarchs averaged approximately one fewer per site from 2004–2013 than during the previous decade, suggesting a recent decline in local abundance of monarch butterflies on their summer breeding grounds in Illinois. Our results demonstrate that seasonal climate and land use are associated with trends in adult monarch abundance, and our approach highlights the value of considering fine-resolution temporal fluctuations in population-level responses to environmental conditions when inferring the dynamics of migratory species.

Semmens, D. J., J. E. Diffendorfer, K. J. Bagstad, R. Wiederholt, K. Oberhauser, L. Ries, B. X. Semmens, J. Goldstein, J. Loomis, W. E. Thogmartin, B. J. Mattsson, L. López-Hoffman. 2018. Quantifying ecosystem service flows at multiple scales across the range of a long-distance migratory species. Ecosystem Services   

​DOI: ​10.1016/j.ecoser.2017.12.002  

Migratory species provide ecosystem goods and services throughout their annual cycles, often over long distances. Designing effective conservation solutions for migratory species requires knowledge of both species ecology and the socioeconomic context of their migrations. We present a framework built around the concept that migratory species act as carriers, delivering benefit flows to people throughout their annual cycle that are supported by the network of ecosystems upon which the species depend. We apply this framework to the monarch butterfly (Danaus plexippus) migration of eastern North America by calculating their spatial subsidies. Spatial subsidies are the net ecosystem service flows throughout a species’ range and a quantitative measure of the spatial mismatch between the locations where people receive most benefits and the locations of habitats that most support the species. Results indicate cultural benefits provided by monarchs in the U.S. and Canada are subsidized by migration and overwintering habitat in Mexico. At a finer scale, throughout the monarch range, habitat in rural landscapes subsidizes urban residents. Understanding the spatial distribution of benefits derived from and ecological support provided to monarchs and other migratory species offers a promising means of understanding the costs and benefits associated with conservation across jurisdictional borders.