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7 Monarch Butterflies and Pollinators Globally, numerous insect species, including many pollinators, have experienced steep pop- ulation declines (Beismeijer et al. 2006, Potts et al. 2010, Powney et al. 2019, Cameron et al. 2011, Goulson et al. 2015). In the United States, 26 butterfly and skipper species and eight bee species are currently listed as threatened or endangered under the U.S. Endangered Species Act (https://ecos.fws.gov/). The decline in pollinator numbers, their importance to natural and agri- cultural ecosystems, and the need for coordinated action to address this decline with expanded efforts to reverse pollinator losses was highlighted in a 2014 Presidential Memorandum (White House 2014). The monarch butterfly (Danaus plexippus) is an iconic species garnering admiration and concern by residents throughout North America. Monarchs exhibit one of the most spectacu- lar animal migrations (Urquhart 1976, Brower 1977). East of the Rocky Mountains in North America, monarchs migrate up to 4,500 km each fall to overwinter in high-altitude fir forests in central Mexico. West of the Rockies, monarchs overwinter in groves along the California coast. In spring, monarchs return to their breeding grounds, with several generations moving and breeding across most of North America throughout the summer. Migrating and breeding butterflies rely on nectar sources for food; to reproduce, monarchs depend solely on larval host plants in the milkweed subfamily (primarily Asclepias spp.). North American monarch populations have declined over the past two decades, an estimated 80% for the eastern population (Brower et al. 2012, Vidal and Rendón-Salinas 2014, Semmens et al. 2016) and 90% for the western population (Shultz et al. 2017; west of the Rocky Mountains), motivating range-wide conservation efforts. The United States, Mexico, and Canada have pledged to reverse declines by improving and expanding habitat (CEC 2008, Pollinator Health Task Force 2015). In 2014, the monarch was petitioned for listing under the U.S. Endangered Species Act. Among multiple factors, including climate change, exposure to pesticides and other toxins, invasive species, disease, and predation (Stenoien et al. 2018, Malcolm 2018), habitat loss is implicated as a primary driver of the population decline (Flockhart et al. 2015, Thogmartin et al. 2017a, Thogmartin et al. 2017b). Two important components in monarch habitat are nectar sources for adult monarchs, provided by a wide variety of blooming plants that benefit pollina- tors in general, and plants for larval development, provided by plants in the milkweed subfamily (Apocynaceae: Asclepiadoideae). Demographic models of the North American eastern monarch population indicate that the breeding season is likely the phase of the monarch life cycle that contributes most to population dynamics (Flockhart et al. 2015, Oberhauser et al. 2017), and loss of milkweed in the core of its breeding range is implicated in the population declines (Pleasants and Oberhauser 2013, Pleasants 2017, Stenoien et al. 2018, Thogmartin et al. 2017a, Thogmartin et al. 2017b, Zaya et al. 2017). This has led to the goal of adding 1.3â1.6 billion stems of milkweed C H A P T E R 1 Background
8 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies in the United States to increase the monarch population to sustainable levels (Pleasants 2017, Thogmartin et al. 2017a). To reach this goal, habitat conservation is needed across all land-use sectors (e.g., agriculture, developed areas, rights-of-way (ROWs)), not just in lands set aside for conservation (Thogmartin et al. 2017b). Suitability of Roadside Rights-of-Way as Habitat for Monarchs ROWs along roads, railways, and power corridors represent a vast opportunity to restore, enhance, and manage habitat for monarchs and other pollinators. There are over 4.1 million miles of roadsides in the United States (Federal Highway Administration 2016), representing approximately 17 million acres of habitat (Ament et al. 2014); in some areas, roadsides comprise the only land easily available as a source of monarch habitat. In contrast to many other land- use types such as agriculture and developed areas, ROW management priorities are largely compatible with providing pollinator habitat. ROWs may provide suitable pollinator habitat if managed in ways that promote and maintain host and nectar plants (Munguira and Thomas 1992, Ries et al. 2001, Saarinen et al. 2005, Hopwood 2008, Skorka et al. 2013, Halbritter et al. 2015). Enhancing milkweed numbers in roadsides could significantly contribute to the goal of adding 1.3â1.6 billion milkweed stems and improve the accessibility of breeding habitat throughout the landscape. In addition, increasing flowering plant resources supports adult monarchs during both breeding and migration seasons. Several studies have shown that roadsides can provide beneficial breeding and foraging habitat to monarchs and other pollinators (Ries et al. 2001, Saarinen et al. 2005, Hopwood 2008, Mueller and Baum 2014, Hanley and Wilkins 2015, Hopwood et al. 2015). Roadsides can also increase connectivity between larger habitat patches, which is likely to lead to increased monarch reproduction (Zalucki and Lammers 2010, Zalucki et al. 2016, Grant et al. 2018). How- ever, there are risks associated with roads, including impacts of vegetation management, par- ticularly mowing at times when monarch eggs and larvae are present (Monarch Joint Venture 2019). Mowing may be conducted for safety reasons, such as the regular mowing of the clear zone. While mowing for traffic visibility kills some monarch larvae, it also maintains open roadside habitat favorable for monarchs, and milkweed regrowth is heavily used by egg-laying monarchs (Alcock et al. 2016, Baum and Mueller 2015, Fischer et al. 2015, Haan and Landis 2019, Knight et al. 2019). Mowing is also used to control invasive species. Invasives, such as wild parsnip (Pastinaca sativa), Johnsongrass (Sorghum halepense), Phragmites (Phragmites australis australis), and sericea lespedeza (Lespedeza cuneate), can take over roadsides, often outcompeting the plant species needed by monarchs and other pollinators; control of these invasives often requires mowing or herbicide treatments that have negative short-term consequences but could prove beneficial (if invasives are controlled) over the long term. Roads also present dangers to butter flies and pollinators (Munoz et al. 2015), including traffic collisions (Skorka et al. 2013, McKenna et al. 2001, Keilsohn et al. 2018), although these effects are likely to be more detrimental in areas of concentrated use during migration (Kantola et al. 2019, Tracy et al. 2019). Monarchs in roadside ROWs may also experience increased exposure to road salts (Snell-Rood et al. 2014), heavy metals (Lagerwerff and Specht 1970, Jaradat and Momani 1999), and insecticides applied to nearby agricultural or developed areas (Krischik et al. 2007, Hopwood et al. 2015, Mogren and Lundgren 2016, Xu et al. 2016), any of which could present risks to monarch survival and development. While roadsides include host plants and nectar plants for monarchs, concern exists that these plants may have less suitable nutritional quality for monarchs, given insecticide spillover from adjacent agriculture and runoff of heavy metals and salts from the road itself. Current research,
Background 9 although still unpublished, suggests that the majority of roadside milkweed is of suitable nutri- tional quality for monarchs (i.e., not toxic). Roadside sodium and heavy metals (especially zinc) vary with traffic volume and distance from the 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; how ever, the majority of the chemicals that show up in these screens are fungicides and herbicides. Current work is clarifying the presence of sub-lethal levels of neonicotinoids. 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, tools have been developed, including a Land- scape Prioritization Model and a Habitat Calculator to quantify variation in roadside habitat quality for monarchs and to assist managers in enhancing the value of these potential habitats. Opportunities for Monarch Habitat in Roadside Rights-of-Way A growing number of transportation agencies have implemented pollinator habitat programs (e.g., Iowa Living Roadway Trust Fund, Illinois Department of Transportation (DOT) Monarch Program, Monarch Highway, and Ohio Pollinator Habitat Initiative). Figure 1 provides exam- ples of signage used along roadways. In addition to these exemplary programs, the research team is finding great interest on the part of many other transportation authorities in providing monarch habitat in their roadways, through groups such as the Rights-of-Way as Habitat Work- ing Group, facilitated through the Energy Resources Center (University of Illinois-Chicago). An example of this high level of interest is that more than 30 transportation and energy sector ROWs management entities are engaging voluntarily in the design of a Monarch Candidate Conservation Agreement with Assurances. This is a formal agreement between the U.S. Fish and Wildlife Service (USFWS) and land managers to engage in important conservation actions for the monarch butterfly (Cardno 2019). Another example of interest in the monarch butterfly is Figure 1. Examples of signs along roadways indicating pollinator projects in transportation rights-of-way.
10 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies the participation by many state departments of transportation in the Mid-American Monarch Conservation Plan written by the Midwest Association of Fish and Wildlife Agencies (Midwest Association of Fish and Wildlife Agencies 2018). There are several information needs associated with the interest in developing monarch habitat pollinator and butterfly habitat from several states. Roadside managers need information to decide where to invest limited resources for maintaining and developing additional monarch habitat. Identifying and selecting priority candidate roadsides for conservation action requires consideration of more criteria than risks or benefits of immediate roadside features such as traffic volume, toxin levels, plant diversity, and habitat width. The value of roadside habitat to monarchs is also determined by the broader landscape context at local, regional, and national scales. For example, at the local level, proximity to arable fields could increase exposure to agri- cultural chemicals, but this risk might be counterbalanced by an overall lack of monarch habitat at a regional scale if roadsides are the only available habitat (even sub-optimal habitat can be better than no habitat). Thus, a nuanced understanding of how habitat availability, connectivity, and other abiotic and biotic factors can interact across local to regional to national scales is germane to effective monarch conservation. Managers who have a limited budget for investing in the creation or res- toration of monarch habitat (Figure 2) would like to know where and how to make the greatest impact per dollar spent. Determining where and how to augment habitat for monarchs in road- sides requires weighing environmental, logistical, and financial factors at multiple landscape scales, while also considering motorist safety concerns. Roadside habitat managers also need information about existing habitat within their roadside ROWs. Critical information about the availability of milkweeds and nectar plants within ROWs habitats is largely missing (but see Hartzler and Buhler 2000, Kasten et al. 2016, Pitman et al. 2018), both generally and specifically within roadside management authorities. In addition, there are no publicly available methods for managers to collect data for such habitat assessments. Comparing roadside areas with scores would enable managers to use data to learn more about how various management actions affect the extent and quality of monarch habitat within their Figure 2. A roadside restoration project in Illinois, Illinois DOT (photo courtesy of Jack Pizzo).
Background 11 jurisdictions. For instance, mowing is needed to maintain safety strips along road margins and is used to control woody and invasive species. However, frequently mowed areas can have fewer species of blooming nectar plants (Halbritter et al. 2015). Many roadside management authori- ties are implementing reduced mowing practices, particularly when monarchs are breeding in their regions, to protect habitat for monarchs and other pollinators. These managers are inter- ested in assessing the habitat characteristics created by such programs. Providing roadside pollinator habitat, either through the creation of new habitat or support of existing habitat, requires identification of optimal best management practices to benefit mon- archs, while reducing other impacts from invasive species and minimizing costs. Historically and currently, roadside best management practices seek to optimize driver safety by provid- ing obstacle-free visual corridors and unimpeded drainage. Roadsides are also managed for aesthetic appeal. Thus, wildlife habitat accommodations must be considered alongside safety requirements and aesthetic expectations (e.g., mowed vegetation). Best management practices have been developed for pollinator habitat in roadside ROWs (Hopwood et al. 2015, Hopwood et al. 2016a,b), and in this project those recommendations were tailored as needed for monarch butterflies to make connections between these best management practices and the other tools for roadside managers. Finally, roadside managers must consider the costs of different conservation actions and the scale at which they can be implemented. Selecting management practices that optimize a positive impact over the largest priority areas requires assessment tools and consideration of multiple cost-benefit scenarios. For example, a state DOT might assess roadsides for potential monarch habitat and identify some that fall into priority monarch conservation areas and pose minimal local risks to monarchs but that currently have poor quality habitat. The DOT could then restore monarch habitat on these sites. Where this habitat is created, it might benefit monarchs, but because of the expense, the DOT might be unable to restore habitat on a broader scale, limiting overall benefits. On the other hand, the DOT might allocate funds or modify management prac- tices to enhance existing habitat. Lower costs might allow for enhancements at a broader scale, with a larger net benefit to monarchs. Some DOTs have noted cost savings by reducing routine mowing of the entire ROW (but this is not always the case as other forms of weed control may be needed, for instance). Reduced mowing (beyond the safety zone) can allow more wildflowers to bloom (e.g., Halbritter et al. 2015), which can benefit monarchs. For example, limiting mowing (beyond the safety/clear zone) to once a growing season (rather than the standard seven times), in the fall along a stretch of highway I-10 in Madison County, Florida, reduced mowing costs by $1,000 per mile and significantly increased wildflower abundance and diversity (Norcini 2014). Tools for Roadside Managers In this project, a set of tools has been developed to help ROWs managers to develop, assess, and manage monarch habitat. Work was focused on four main products. Product A: Landscape Prioritization Model for Roadside Habitat for Monarchs The Landscape Prioritization Model for Roadside Habitat for Monarchs is a computer-based model that helps roadside ROW managers to visualize roads in their state relative to landscape- scale factors that influence monarch habitat quality. When roadside managers are determining where to invest in creating monarch habitat in the roadside ROWs, the Landscape Prioritiza- tion Model provides information about the surrounding landscape that may be used to rank roadsides according to their context. The model is a way to visualize various habitat functions
12 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies in the landscape and could be used to target particular areas or set up a sampling scheme. It may be used to describe different settings into which restoration or habitat development practices could be implemented. The model uses publicly available national land cover, cropland, and road datasets in an Esri Geographic Information System (GIS). The latter requires an ArcGIS for desktop basic license with the spatial analyst extension. The model provides options for cus- tomization with more specific data. It is designed to be run at the state scale, and then managers may examine roadsides at the state, county, road system, or bioregional scale within states. Product B: Rapid Assessment of Roadside Habitat for Monarchs The (RA) of Roadside Habitat for Monarchs is a quick and simple data collection tool for roadside vegetation managers or other transportation professionals to assess current mon- arch habitat in their roadside ROWs. This tool enables managers to complete a brief (less than 20 minutes) survey on a mobile data collection device, such as a tablet or smartphone, or on paper at specific locations or locations selected in a systematic (e.g., every half mile along a stretch) or random way to represent the road system of interest. The RA focuses on plants that provide monarch habitat (milkweed for reproduction and nectar plants for foraging), as well as threats and management in the ROW. RA data collected in Esri Survey123 directly feed into the Roadside Monarch Habitat Calculator to give monarch habitat quality scores for compar- ing sites across the assessed locations. These protocols may also be employed after management to assess effectiveness of conservation actions and over years to track the persistence of habitat through time. Product C: Roadside Monarch Habitat Calculator The Roadside Monarch Habitat Calculator is a data-driven scoring system that rates sites for their habitat quality for monarchs. This product can be used to evaluate existing roadside habitat quality for monarchs and also to evaluate the effectiveness of management actions after their employment. The Habitat Calculator incorporates four functional components of habitat: breeding habitat (milkweed), foraging habitat (nectar plants), threats and context (roads, invasive species, and adjacent land use), and management (mowing and herbicide use). Each assessed site is given a Monarch Habitat Quality Score, which enables managers to compare sites within their state or road system. Managers can also view component scores for the four main func- tional components. The tool uses data collected in the Rapid Assessment; calculations are done automatically in Esri Survey123, and results may be viewed in spreadsheet or map formats. Product D: Best Management Practices and Decision Support Decision support is a theme that weaves throughout the project. It drives the production of all of the products. The focus is on helping managers make decisions about habitat installation and management as well as communications with their staff and public about these decisions. Based upon information derived in the Landscape Prioritization Model or the Roadside Monarch Habitat Calculator on a given roadsideâs habitat score, context-specific management recommendations are needed to guide selection of best management actions to enhance and maintain habitat for monarchs and mitigate threats. While general guidelines for managing roadside habitat for pollinators are available, this information is often not accessible to roadside management practitioners. Based on the research teamâs annual meeting, a logical prototype of user-defined objectives and management actions was built. This developed into a decision- support tree representing various decisions managers can make that affect their ability to provide monarch habitat in their ROWs. The prototype can be used to orient managers to appropriate
Background 13 resources supporting each decision. Surveys, interviews, and webinars have provided informa- tion to share back out in web-based resources. Through a gap analysis, areas needing more decision-support information were identified. For these areas, project participants developed simple, easy to read resources for print or web access, including an herbicide fact sheet, regional milkweed guides, and a comprehensive list of frequently asked questions. Tool Use Scenarios, Interactions Between the Products The Landscape Prioritization Model may be used to locate sampling areas for a manager who would like to sample roadside habitats with the RA. One could select roadsides repre- senting low and high potential for habitat development according to the landscape model and then sample randomly or systematically among them. Or, if one were interested in planting a high-diversity, monarch-friendly seed mix in one of several construction zones, then one could assess areas that appeared to be in close proximity to other habitat areas. Conversely, place habitat in an area where there appears to be a need for a patch of connecting habitat, consulting the best management practices provided through the project (Figure 3). Below is a flow chart (Figure 4) illustrating how the RA, Habitat Calculator, and best man- agement practices relate to one another. Figure 5 is a diagram showing the workflow process a manager might use in developing monarch habitat within their roadside corridors using decision-support tools developed in this project. Figure 3. Schematic indicating relationship between components in this project (BMP = best management practices). Figure 4. Flowchart illustrating the relationship among project elements: habitat assessment, habitat calculation, and best management practices.
14 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies Figure 5. Workflow diagram illustrating how a manager may assess roadsides using tools developed in this project. See Appendix A for the full-sized diagram.
