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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies. Washington, DC: The National Academies Press. doi: 10.17226/25693.
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© 2019 National Academy of Sciences. All rights reserved. ACKNOWLEDGMENTS The research for this document was conducted through one or more programs administered by the Cooperative Research Programs (CRP) of the Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine: • Airport Cooperative Research Program (ACRP) research is sponsored by the Federal Aviation Administration (FAA). • Hazardous Materials Cooperative Research Program (HMCRP) research is sponsored by the Pipeline and Hazardous Materials Safety Administration (PHMSA). • National Cooperative Freight Research Program (NCFRP) research is sponsored by the Office of the Assistant Secretary for Research and Technology. • National Cooperative Highway Research Program (NCHRP) research is sponsored by the American Association of State Highway and Transportation Officials (AASHTO), in cooperation with the Federal Highway Administration (FHWA). • National Cooperative Rail Research Program (NCRRP) research is sponsored by the Federal Railroad Administration. • Transit Cooperative Research Program (TCRP) research is sponsored by the Federal Transit Administration (FTA) in cooperation with the Transit Development Corporation. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply endorsement by TRB and any of its program sponsors of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. DISCLAIMER This is an uncorrected draft as submitted by the research agency. The opinions and conclusions expressed or implied in the report are those of the research agency. They are not necessarily those of the Transportation Research Board, the National Academies or the program sponsors. This pre-publication document IS NOT an official publication of the Cooperative Research Programs; the Transportation Research Board; or the National Academies of Sciences, Engineering, and Medicine. Recommended citation: Cariveau, A. B., W. Caldwell, E. Lonsdorf, C. Nootenboom, K. Tuerk, E. Snell- Rood, E. Anderson, K. A. Baum, J. Hopwood, and K. Oberhauser. 2019. Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies. Pre-publication draft of NCHRP Research Report 942. Transportation Research Board, Washington, D.C.

ii A U T H O R A C K N O W L E D G M E N T S We thank Iris Caldwell and Klaudia Kuklinski at the Energy Resources Center (University of Illinois – Chicago) for their help with the Metrics and Targets Taskforce in the review of other pollinator habitat rating systems. We thank Emily Geest, Jeremy Kaplan, Ashley Knoch, Nick Haas, Grace Haynes, and Patrick Parish for the tireless effort collecting field data for the project. Many thanks to members of the Snell-Rood lab working on aspects of a related project (funded by the Minnesota Environment and Natural Resources Trust Fund) on the nutrition of roadside plants for pollinators -- in particular, Megan Kobiela, Tim Mitchell, Alex Shepard, and Lauren Agnew, in addition to help in the field from Rebecca Meyer and Annika Herdtle. We thank Laura Lukens, Kyle Kasten, and Cora Lund Preston at Monarch Joint Venture for their help in designing and implementing the project. We thank all of the members of our Research Advisory Group and departments of transportation managers who assisted us throughout the project, in particular Rich Baker (Minnesota Department of Natural Resources), Chris Smith and Tina Markeson (Minnesota Department of Transportation), Alyssa Barrette and Christa Schaefer (Wisconsin Department of Transportation), Stephanie Dobbs and Susan Hargrove (Illinois Department of Transportation), Iris Caldwell (Energy Resources Institute, University of Illinois-Chicago), Dennis Markwardt (Texas Department of Transportation), Dennis Martin (Oklahoma State University), and Wayne Thogmartin (U.S. Geological Survey). We also thank the members of the Advisory Panel: Bill Rogers (our NAS program officer), Stacy Armstrong, Larry Bonner, David Cohen, Michael Gale, Amanda Gendek, Susan Hargrove, Meghan Hedeen, Mark Masteller, and Chris Smith. The roles of the authors were as follows. Alison Cariveau (Monarch Joint Venture; MJV) led the project overall and was lead author for the report. Karen Oberhauser was the original Principal Investigator at the University of Minnesota; when KO moved to University of Wisconsin, Emilie Snell-Rood became Principal Investigator at the University of Minnesota. Wendy Caldwell oversaw the project for MJV and provided feedback and guidance throughout the project. Kristen Baum (Oklahoma State University) was involved in the design of the Rapid Assessment protocol and led the field testing in Oklahoma. Erik Anderson (Environmental Incentives) was involved in the design of the Habitat Calculator, conducted user interviews, and created the manager workflow diagram. Eric Lonsdorf and Chris Nootenboom (Institute on the Environment, University of Minnesota) developed the Landscape Prioritization Model and authored the chapter and user guide. Karen Tuerk (MJV) designed and completed all of the programming for the Monarch Habitat Evaluator in Survey123, wrote the user guide, and was GIS specialist for the project. Jennifer Hopwood (Xerces Society for Invertebrate Conservation) co-led the best management practices and decision support team with Alison Cariveau and authored Frequently Asked Questions, Monarchs, Herbicides, and Weeds, and a set of regionally specific milkweed identification handouts.

iii C O N T E N T S SUMMARY ............................................................................................................................................................... vi Overview ...................................................................................................................................................................................................... vi Findings ........................................................................................................................................................................................................ vi Future Research Needs ....................................................................................................................................................................... viii Recommendations ................................................................................................................................................................................... ix Conclusions ................................................................................................................................................................................................. ix Opportunities ............................................................................................................................................................................................... x CHAPTER 1 ............................................................................................................................................................... 1 Background ......................................................................................................................................................... 1 Monarch Butterflies and Pollinators ................................................................................................................................................. 1 Suitability of Roadside Rights-of-way as Habitat for Monarchs ........................................................................................... 2 Opportunities for Monarch Habitat in Roadside Rights-of-Ways ........................................................................................ 3 Tools for Roadside Managers ............................................................................................................................................................... 5 Product A: Landscape Prioritization Model for Roadside Habitat for Monarchs ................................................... 5 Product B: Rapid Assessment of Roadside Habitat for Monarchs ................................................................................. 5 Product C: Roadside Monarch Habitat Calculator ................................................................................................................ 6 Product D: Best Management Practices and Decision Support ....................................................................................... 6 Tool Use Scenarios, Interactions between the Products .................................................................................................... 6 CHAPTER 2 ............................................................................................................................................................... 9 General Research Approach .............................................................................................................................. 9 Meetings ........................................................................................................................................................................................................ 9 Webinars ..................................................................................................................................................................................................... 10 Survey of Transportation Managers ............................................................................................................................................... 10 User Profile Interviews ......................................................................................................................................................................... 10 Reviewing Existing Tools and Protocols ....................................................................................................................................... 11 Expert User Testing ................................................................................................................................................................................ 12 Field-testing with Biotechnician Crews ........................................................................................................................................ 12 CHAPTER 3 ............................................................................................................................................................ 14 Product A: Landscape Prioritization Model for Roadside Habitat for Monarchs ...................................... 14 Introduction ............................................................................................................................................................................................... 14 Habitat Modelling .................................................................................................................................................................................... 15 Milkweed suitability ......................................................................................................................................................................... 16 Nectar availability ............................................................................................................................................................................. 17 Pesticide exposure (Ei) .................................................................................................................................................................... 17 Overall habitat quality (Hi) ............................................................................................................................................................ 17 Core habitat .......................................................................................................................................................................................... 17 Roadside Potential .................................................................................................................................................................................. 18 Benefits .................................................................................................................................................................................................. 18 Potential roadside habitat (Ai) ............................................................................................................................................... 18 Augmenting adjacent habitat (Qi) ........................................................................................................................................ 19 Roadside connectivity (Di) ...................................................................................................................................................... 19 Risks ........................................................................................................................................................................................................ 20 Vehicle collision risk (Vi) .......................................................................................................................................................... 20 Chemical exposure from cars (Ci) ........................................................................................................................................ 21 Roadside suitability overall ................................................................................................................................................................ 21 Data sources .............................................................................................................................................................................................. 21 Discussion ................................................................................................................................................................................................... 23

iv CHAPTER 4 ............................................................................................................................................................ 24 Product B: Rapid Assessment of Roadside Habitat for Monarchs............................................................... 24 Background ................................................................................................................................................................................................ 24 Rapid Assessment Protocol ........................................................................................................................................................... 27 Integrated Monarch Monitoring Program Methods........................................................................................................... 27 Field Trials ............................................................................................................................................................................................ 28 Minnesota – Protocol Comparison ............................................................................................................................................. 29 Minnesota - Broadscale Surveys ................................................................................................................................................. 29 Statistical Analyses ..................................................................................................................................................................... 30 Field Trials - Oklahoma ................................................................................................................................................................... 31 Field Surveys with Multiple Protocols ..................................................................................................................................... 35 Milkweed density......................................................................................................................................................................... 35 Monarch eggs and larvae.......................................................................................................................................................... 36 Blooming nectar plants ............................................................................................................................................................. 37 Discussion ................................................................................................................................................................................................... 39 CHAPTER 5 ............................................................................................................................................................ 44 Product C: Roadside Monarch Habitat Quality Calculator ........................................................................... 44 Background ................................................................................................................................................................................................ 44 Methods ....................................................................................................................................................................................................... 45 Monarch Breeding Habitat ............................................................................................................................................................ 45 Milkweed Abundance ................................................................................................................................................................ 45 Milkweed Species Composition ............................................................................................................................................. 46 Adult Monarch Foraging Habitat ................................................................................................................................................ 47 Nectar Plant Abundance ........................................................................................................................................................... 47 Nectar Plants: number of species ......................................................................................................................................... 48 Nectar Plants: number of native species ........................................................................................................................... 49 Context/Threats ................................................................................................................................................................................. 50 Adjacent Land Use ....................................................................................................................................................................... 50 Roads as Sources of Chemical Inputs and Vehicular Collisions .............................................................................. 51 Noxious weeds .............................................................................................................................................................................. 52 Management ........................................................................................................................................................................................ 53 Herbicide application ................................................................................................................................................................. 53 Mowing ............................................................................................................................................................................................. 53 Running the Calculator ................................................................................................................................................................... 54 Field testing the Calculator ........................................................................................................................................................... 54 Results .......................................................................................................................................................................................................... 54 Minnesota ............................................................................................................................................................................................. 55 Oklahoma .............................................................................................................................................................................................. 58 Discussion ................................................................................................................................................................................................... 59 CHAPTER 6 ............................................................................................................................................................ 61 Product D: Best Management Strategies and Decision Support .................................................................. 61 Survey of Transportation Managers ............................................................................................................................................... 61 Methods ................................................................................................................................................................................................. 61 Survey Questions ............................................................................................................................................................................... 61 Overview ......................................................................................................................................................................................... 61 Geographical .................................................................................................................................................................................. 62 Rights-of-Way Width.................................................................................................................................................................. 62 Field Assessment ......................................................................................................................................................................... 62 Management Questions ............................................................................................................................................................ 62 Open Input ...................................................................................................................................................................................... 63 Survey Results..................................................................................................................................................................................... 63 Survey Conclusions ........................................................................................................................................................................... 68

v User Profile Interviews ......................................................................................................................................................................... 68 Methods ................................................................................................................................................................................................. 68 Findings ................................................................................................................................................................................................. 68 Habitat Calculator Use Scenarios ............................................................................................................................................... 69 Most Common Users ........................................................................................................................................................................ 69 Decision Support Tree ........................................................................................................................................................................... 70 Decision Support Materials ................................................................................................................................................................. 73 Existing resources ............................................................................................................................................................................. 73 Nectar Plant Guides .................................................................................................................................................................... 73 Locating Plant Materials ........................................................................................................................................................... 73 Best Management Practices .................................................................................................................................................... 73 Revegetation Guidance.............................................................................................................................................................. 73 Case Studies ................................................................................................................................................................................... 74 New Materials Developed .............................................................................................................................................................. 74 Series of Frequently Asked Questions (FAQ's): Managing Roadside Habitat for Monarchs ...................... 74 Best Management Practice Guide: Herbicides, Weeds, and Monarchs ................................................................ 89 Regional Milkweed Identification Field Sheets .............................................................................................................. 94 Discussion ................................................................................................................................................................................................... 95 CHAPTER 7 ............................................................................................................................................................ 96 Conclusions and Suggested Research ............................................................................................................. 96 REFERENCES ......................................................................................................................................................... 99 ACRONYMS .......................................................................................................................................................... 103 APPENDIX A: Diagram of Workflow for Use by Managers of Roadside Habitat for Monarchs Decision Support Tools ................................................................................................................................ A-1 APPENDIX B: User Guide for the Landscape Prioritization Model for Roadside Habitat for Monarchs ........................................................................................................................................................... B-1 APPENDIX C: Rapid Assessment of Roadside Habitat for Monarchs: Field Protocol and Datasheet .......................................................................................................................................................... C-1 APPENDIX D: User Guide for Rapid Assessment of Roadside Habitat for Monarchs and Habitat Calculator: Monarch Habitat Evaluator Tool ...................................................................... D-1 APPENDIX E: Best Management Practices Resource Sheet: Monarch Butterflies, Weeds, and Herbicides ......................................................................................................................................................... E-1 APPENDIX F: Regionally Specific Roadside Milkweed Recognition Fact Sheets ......................... F-1

vi S U M M A R Y Overview This project examined the potential for roadway corridors to provide habitat for monarch butterflies and developed tools for roadside managers to optimize potential habitat for monarch butterflies in their road rights-of-way. We developed the following products through the project, all of which are available to interested departments of transportation: – Product A: A Landscape Prioritization Model for Roadside Habitat for Monarchs to assist roadside managers with identifying locations that are both compatible with their road and ROW maintenance objectives and ranked in suitability for monarch habitat conservation. The national GIS model can be enhanced with state or more local information to further refine prioritization of sites. – Product B: A Rapid Assessment of Roadside Habitat for Monarchs protocol enables roadside managers to quickly survey a roadside area to evaluate the current status of the habitat quality for monarchs. The assessment focuses on functional components of monarch habitat: breeding habitat, foraging habitat, threats and landscape context, and roadside vegetation management practices. Data are entered into Esri Survey123, software used by most state transportation authorities, the survey may be customized by each state, and results are easily tracked and summarized within each state department of transportation. – Product C: The Roadside Monarch Habitat Calculator transforms Rapid Assessment data into monarch habitat quality scores, metrics that can be used to compare sites within a road system or state and inform land managers of needed conservation actions. Data gathered in this assessment create an adaptive management feedback loop in order to track success of efforts through time and improve future conservation practices. The functional components of the rapid assessment are combined into one monarch habitat quality score but also reported independently to inform adaptive management. – Product D: Decision support tools for roadside managers were developed to help align road authority objectives and regulations with conservation goals in a way that is economically and environmentally additive. A survey of roadside management entities across the U.S. helped identify areas where roadside management objectives and barriers intersect with conservation objectives, and findings were used to inform the tools developed through this project to ensure the tools were adopted by and useful to road authorities. Online and print materials were also developed to support land managers in their conservation-oriented decisions, including a decision tree, milkweed guides, a weed and herbicide resource sheet, and a set of frequently asked questions. Products A through D are available online (https://monarchjointventure.org/roadsidehabitat) for departments of transportation who want to learn more about the habitat in the road corridors they manage. We published the tools in Esri products that are readily in use by most transportation departments. Products B and C are combined into a Roadside Monarch Habitat Evaluator module that may be customized by each state for its use. Managers may then view their site data and habitat scores in a spatial map layout or in a spreadsheet depending on their information needs. Findings In our survey of roadside managers as well as by interactions with transportation professionals throughout the project, we found a high degree of interest and dedication to providing pollinator and monarch habitat along roadways. Our investigations indicated that variable amounts of knowledge and time that could be

vii allocated to pollinator work. Funds for pollinator work are generally extremely limited, so cost-savings from altered management is an important topic. We found tremendous variation in the reported use of key management techniques including mowing and herbicide application, indicating opportunities for alteration in the area of vegetation management. In our field trials, we found high quality monarch breeding habitat in roadside rights-of-way areas. Field studies in Minnesota and Oklahoma showed high levels of milkweed and monarch use of milkweed in roadside rights-of-way, as well as nectar plants. We also found concurrence between our Rapid Assessment of Roadside Habitat for Monarchs to another more intensive monarch habitat monitoring protocol. Our study addressed the question of whether habitat along roads is suitable for monarch butterflies. Our research including data collected in this project suggests that roadsides are promising habitat for monarchs. With respect to host plants, over half of randomly selected roadsides contain milkweed and surveys detailed in this report highlight densities over 2000 stems of milkweed per mile. Roadside sites also include a variety of nectar plants beneficial not only to monarchs but to a diversity of pollinators. We reviewed risks to monarchs and their habitat in roadside corridors, including impacts of vegetation management, particularly mowing that is required for maintenance of safety standards. While mowing for traffic visibility kills some monarch larvae, it also maintains open roadside habitat favorable for monarchs, can be used to control invasive and undesirable plant species, and milkweed re-growth is heavily used by egg-laying monarchs. Roads also present danger of traffic collisions for monarchs, although these effects appear to be more concentrated in particular funnel areas during migration. Monarchs in roadside rights- of-way may also experience increased exposure to road salts, heavy metals, and insecticides applied to nearby agricultural or developed areas any of which could present risks to monarch survival and development. However, current research, although still unpublished, suggests that the majority of roadside milkweed is of suitable nutritional quality for monarchs (i.e., not toxic). Roadside sodium and heavy metals (especially zinc) vary with traffic volume and distance from road. Most metal levels are below what is toxic for monarchs. While sodium levels do reach toxic levels, this seems to be limited to milkweeds along the highest traffic roads and in the buffer zones that are often mowed just adjacent to the road. Screens for pesticides do find residues on at least a quarter of roadside milkweeds, however, the majority of the chemicals that show up in these screens are fungicides and herbicides. Current work is clarifying the presence of sublethal levels of neonicitinoids. Taken together, this work in progress suggests that most roadside milkweed, especially along the majority of roads (which are moderate to low traffic volume) harbor milkweed of suitable nutritional quality for monarchs. In summary, threats along roadway corridors exist for monarchs and other pollinators, but in the context of the amount of habitat needed for recovery of sustainable populations, roadsides are of vital importance. As detailed in this report, we have developed tools including a landscape model and a habitat calculator to to assist managers in understanding the habitat they manage and improving their ability to enhance these habitats through adaptive management. The Landscape Prioritization Model developed in this project is the first of its kind at this scale. It provides a transportation manager the ability to evaluate the landscape in their state with regard to areas where diverse roadside habitat could complement already existing natural habitats or where high-quality roadside plantings might create a corridor of suitable habitat where there is otherwise very little. In addition, this model depicts roads and their associated hazards in a way that helps managers to think about the importance of traffic volume, traffic speed, and right-of-way width, all factors that can potentially affect the roadside environment for monarchs. Together, this landscape information and road metrics inform managers’ understanding of their road systems in a novel way.

viii The Rapid Assessment of Roadside Habitat for Monarchs is a way for transportation managers to readily assess the habitat currently in their rights-of-way, and to track it through time. While many land management entities often lack time and capacity to conduct habitat assessment work, this tool was designed to be quick and easy to implement with different skill levels and also feeds into broader scale monarch and habitat monitoring initiatives and tracking efforts. Tracking and evaluating monarch habitat projects using the Rapid Assessment creates a feedback loop of information that will tell rights-of-way managers the baseline quality of their site, as well as continued tracking of how the project is doing. In turn, this will provide a valuable data set that will improve the seed mix design and habitat management practices implemented by the land management authority as they learn what is performing well, and what may not be. Not only will this reduce costs over time, but if applied in an adaptive management framework, the quality of the habitats for monarchs and pollinators should also improve (or minimally be sustained) over time. The Roadside Monarch Habitat Calculator provides managers an easy way to interpret breakdown of the functional components of the habitat. Using data collected through the Rapid Assessment, it provides users with scores about how a particular project or site area is performing in the areas of monarch breeding habitat, foraging, landscape context and threats, and management. The scores for each of these components are combined into an overall score, but also presented independently such that a land manager can pinpoint specific problem areas that could be improved on that site. For example, if the breeding habitat score for a site is low, this means that it is lacking sufficient milkweed host plants for monarchs. Actions to increase the milkweed density at that site could improve the habitat score over time. The Calculator also provides a reportable metric that can be used in internal or external reporting. These scores can be viewed in an online map or spreadsheet format. We provided several types of decision support tools in response to the needs of the roadside management community. We recognized that there were several information needs, including guidance on mowing, herbicide applications, milkweed identification, and native seed guides (including milkweed). We identified some resources that were currently available and linked to them in our online manager toolbox. We developed several other materials that were not yet in existence. We developed regionally appropriate Milkweed Guides, single-sheet handouts that may be given to road management crews to help them to identify milkweed growing in their roadside corridors and choose appropriate management actions, such as avoiding the application of herbicide to milkweed and planning mowing activity to avoid when monarchs are breeding in their locality. We developed a Monarch Butterflies, Weeds, and Herbicides resource sheet. Recognizing that road managers operate within single states, we have that facilitated information sharing across states, including case studies. We have also developed a set of frequently asked questions and answers to optimizing information sharing about best practices Future Research Needs There are several gaps in our knowledge where expert opinion was used to develop the project tools. To improve the tools over time, we’ve identified the following research priorities: – Exploration of how field level habitat quality values (such as derived from the habitat calculator) and use of roadside areas by monarchs relate to the landscape factors depicted in the Landscape Prioritization Model. – Milkweed and nectar plant abundance in various land-use types and regions of the US, and how these values relate to the habitat quality within road rights-of-ways in various regions – Response of milkweeds, nectar plants, and monarch eggs and larvae to management practices, including mowing and haying at various times of year

ix – Differences in utilization of various species of milkweed by monarchs in roadside areas – Quantification of traffic collisions (adult mortality) in relation to production of monarchs in roadside habitat (and in relation to traffic volume, speed, and surrounding habitat type) – Chemical exposure risks to monarchs in highly agricultural or heavy traffic areas, e.g., >30,000 cars a day typical of highly urbanized areas (pesticides and vehicle/road chemical runoff/drift) – Effective treatments of invasive species to enhance future restoration activities – Economic studies on the short-, mid-, and long-range costs of implementing monarch/pollinator programs within a roadside management entity, which may be influenced by the upcoming proposed listing decision by USFWS for species listing under the Endangered Species Act – Assessing the value of roadsides as important habitat corridors in “habitat deserts,” such as areas in the Midwest that are dominated by agriculture Recommendations – We recommend that roadside management authorities use the landscape prioritization model to identify areas for monarch breeding habitat restoration or improved management where fewer threats to monarchs are posed. – We recommend that roadside managers assess their roadside rights-of-way with the Rapid Assessment protocol to gain valuable information about the roadside areas they manage. This could take the form of an inventory of the habitat they manage, to find out the proportion of areas that provide high quality habitat, or to estimate the milkweed density their road system provides, or other similar objectives. Managers also may wish to compare the habitat characteristics for areas under different management regimes, such as modified mowing practices, or areas that have been restored with a particular seed mix. For all pre-, post-, and long-term restoration or improved management projects, assessment of the habitat builds a base of information that can be used in an adaptive management framework to improve benefit to monarchs and pollinators and cost-effectiveness of conservation practices. – The habitat quality scores generated automatically by the habitat calculator may be used to identify high quality sites and sites where habitat could be improved. – We encourage departments of transportation to use the decision support tools and best management practices information made available through our website to support their monarch conservation efforts. Educational objectives can be built into roadside management programs to engage diverse stakeholders, train management staff about how to properly maintain diverse native plant communities, and to increase awareness about monarch and pollinator conservation needs. Conclusions Land use changes have caused dramatic losses of habitat for monarchs across much of their breeding and migratory range. Roadside habitats provide a unique opportunity to influence habitat availability on a large scale (number of acres) and in distribution across the landscape. In some urbanized and agricultural parts of the monarch range, roadside habitats are a primary source of breeding habitat, and therefore increasing the abundance and quality of those critical areas is an important contribution to a larger strategy to conserve monarchs, other pollinators, other wildlife species, and to provide other important ecological services. It is possible that in these “habitat deserts” roadsides may act as important corridors or refuge areas during migration. We have developed an initial set of tools and decision support mechanisms to support roadside managers in these efforts. This project reflects partnership between conservation organizations, universities, and roadside authorities to enhance the objectives of all parties by developing and improving strategies for monarch conservation. An ‘all hands on deck’ approach to conservation is needed to protect monarch butterflies, and this work assists transportation authorities in pursuing opportunities to implement proactive

x and voluntary approaches to provide pollinator habitat in roadway corridors. In doing so, transportation agencies can also appeal to the growing public attention and calls for monarch and pollinator conservation. Opportunities Moving forward, we would like to pursue implementation to more widely promote the findings of this project through a) a well-designed, interactive website tailored to the needs of roadside managers, b) trainings in how to use the tools created, c) scientific writing regarding the outcomes of our field research, and d) more outreach and public relations around best management practices, case studies, and sharing of successes across states. This work has also highlighted opportunities for future research and assessment. For instance, future research needs have highlighted knowledge gaps with respect to mowing, adult mortality from collisions and the value of roadside corridors isolated from core habitat – all research topics that would benefit from agency-university interaction and collaboration. Our work has also identified a need for integrating our recommendation tools with the budget and labor needs of individual transportation agencies – for instance, determining the optimal course of action based on habitat calculator scores will depend on the agency. An agency with a low budget may invest in preserving the highest value roadsides, while an agency with a modest budget for restoration may invest in roadsides with high potential value, but current low to moderate habitat. As agencies begin to use these tools, there are many opportunities for assessment and refinement of the tools and recommendations. This project has also created several opportunities with respect to broader conservation goals. First, while we have focused on monarchs, this species serves as a flagship species for many other species, both plant and animal, that support natural ecological functions. Preserving monarch habitat, and associated nectar plants and host plants (which are a great nectar plant for many insect pollinators) no doubt has beneficial impacts on hundreds of other species. This is particularly important given recent outcries of a pending “insect apocalypse” as negative effects of pesticide use, habitat destruction and climate change are leading to precipitous declines across over 40% of insect species (Sanchez-Bayo and Wychhuys 2019). Second, while this work has focused on roadside rights-of-way, many of the tools and recommendations are relevant to other types of rights-of-way. Rights-of-way alongside railroads, power lines, and gas lines also present valuable opportunities for habitat as they can act as habitat corridors and cover millions of acres across the country. There is overlap between outcomes of this project and management decisions related to mowing, landscape context, invasive species control, collisions, chemical exposure, and prioritization of sites for restoration. We hope that some of the general lessons learned in roadside management for monarchs can also be applied to conservation opportunities in other rights-of-way.

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The charismatic and familiar monarch butterfly serves as a flagship species for pollinator conservation, and gives rights-of-way entities opportunities to engage a diverse array of stakeholders who are invested in not only restoring monarch numbers to sustainable levels, but also mitigating many other environmental and economic issues.

This pre-publication draft of the TRB National Cooperative Highway Research Program's NCHRP Research Report 942 Pre-Pub: Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies examines the potential for roadway corridors to provide habitat for monarch butterflies and developed tools for roadside managers to optimize potential habitat for monarch butterflies in their road rights-of-way.

As part of the project, several products were developed, all of which are available to interested departments of transportation.

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