Pacific Southwest RegionCalifornia, Nevada and Klamath Basin
The Monarch Butterfly Story...
Photo Credit: Flickr/Creative Commons
Monarchs face many risks that are resulting in declining populations in both the eastern and western parts of their North American range. The largest impacts come from the loss of habitat for breeding, migrating, and overwintering. In addition, pesticides that are used to control insects and weeds have harmful unintended consequences for monarchs, a changing climate may be making some habitat less suitable and forcing changes in migratory patterns, and monarchs face many risks from natural enemies, such as predators, parasitoids, and diseases.
The loss of milkweed in agricultural fields is a major cause of decline in monarchs, though there are other factors contributing to the decline in milkweed availability. Herbicide application and increased mowing in roadside ditches and agricultural margins is eradicating milkweed habitat even more from rural areas.
If managed appropriately, roadsides could provide millions of acres of habitat suitable for monarchs and other pollinators.
These areas are often mowed or sprayed regularly throughout the growing season to control weedy species, but if transformed into a native plant community, they could require signficantly less maintenance once established while providing important habitat. If mowing is used to manage weedy species or invasives, it is best to do it during times when monarchs will be least affected by the disturbance. In addition, leaving sections of the habitat untouched will allow pollinators and other wildlife to find refuge in those areas while the disturbed portion of the site recovers.
Urban sprawl and continuing industrial development are also major factors influencing the decline in quality monarch habitat. Other anthropogenic factors, such as ozone pollution or increased carbon dioxide levels, can affect the health and distribution of milkweed plants.
Monarch Joint Venture: 2018 Monarch Conservation Implementation Plan
The 2018 Monarch Conservation Implementation Plan is designed to help facilitate cooperation and coordination in the United States to help accomplish our nation's goals for monarchs and other pollinators.
Photo Credit: USFWS
It identifies and prioritizes current important actions for monarch conservation in the U.S., and promotes cooperation between diverse organizations working together to achieve the goals outlined in the plan.
The plan was originally derived from the North American Monarch Conservation Plan (CEC, 2008), and is updated annually by the Monarch Joint Venture (MJV) partnership. As a national coordinating body, the MJV encourages the widespread use of this plan and will help identify opportunities for collaboration between different entities.
Recognizing that it will take an "all hands on deck" approach to reach our nationâ€™s population and habitat targets, this plan was created in an effort to better coordinate monarch conservation in the U.S.
Monarch habitat Needs
Milkweed is an essential feature of quality monarch habitat. There are over 100 species of milkweed in North America, though monarch conservation organizations have prioritized species for each region of the U.S. The Monarch Joint Venture has produced a Milkweed Fact Sheet describing these priority species.
Photo Credit: Courtney Celley/USFWS
Many milkweed species are very hardy and grow in various landscapes. Common places to find milkweed include short and tall grass prairies, livestock pastures, agricultural margins, roadsides, wetland areas, sandy areas, and gardens. Though monarchs do use sites with very few milkweed plants, more plants can support more monarchs.
Fewer plants may result in higher per plant monarch density, which can increase the risk of spreading disease and can result in competition for food between larvae. Including native milkweed species in your monarch habitat is extremely important. Not only does native milkweed offer a food source for monarch larvae, but it provides nectar for a variety of other pollinators and also provides habitat for many other organisms.
Native plants are well adapted for the climatic conditions of their region and are easy to care for. Diversity in native plant communities supports many native insects and also provides a number of ecological benefits, such as erosion reduction and filtration.
Unlike larvae that rely only on milkweed to survive, adult monarchs use diverse nectar sources for food. Nectar plants are a key component to prime habitat for monarchs and other pollinators.
Spring blooming nectar plants (blooming approximately March 20 -- June 1) fuel the monarch migration northward from Mexico and inland from the California coast. Without abundant nectar sources through the migratory corridors, monarchs are less likely to survive and may not be able to reproduce successfully.
Summer blooming nectar sources (blooming approximately June 2 -- August 15) throughout the breeding range are vital to sustain a healthy breeding population.
Fall blooming nectar plants (blooming approximately August 16 -- October 30) are equally important; monarchs rely on abundant nectar sources in the fall to store enough energy not only to survive the long journey to their overwintering sites, but also to survive winter with very minimal nectar availability.
While non-native species can be used for nectar, native nectar plants are significantly more beneficial to an ecosystem. Native plants are well suited for the climatic conditions of an area and are responsible for important ecosystem functions, such as erosion control and filtration.
The area surrounding a monarch habitat can influence monarch use of a site and survival. Land use changes have caused natural areas to be fragmented into smaller, more distant parcels of land disbursed throughout an ecosystem. Surrounding areas covered by natural vegetation are more beneficial to monarchs than surrounding land that has been altered by development or agriculture.
Natural vegetation surrounding any wildlife habitat reduces the risk of danger by human contact. Milkweed habitat mixed within human inhabited areas is important for monarch populations, but it can increase the risk of injury or death to monarchs by vehicles or human activity, such as pesticide use.
Monarch breeding habitats in close proximity to each other allow monarchs to find suitable habitat without traveling long distances.
- Managing Monarchs in the West: Best Management Practices for Conserving the Monarch Butterfly and its Habitat
- Conservation Status and Ecology of the Monarch Butterfly in the United States
- State of the Monarch Butterfly Overwintering Sites in California
- Protecting California's Butterfly Groves: Management Guidelines for Monarch Butterfly Overwintering Habitat
- July 2016 Monarch Update: Helping Monarch Conservation Take Flight
- Milkweeds and Monarchs in the Western U.S.
Western Monarch Story map
The monarch butterfly is one of the most recognizable species of wildlife in all of America. They undertake one of the world's most remarkable and fascinating migrations, traveling thousands of miles over many generations from Mexico, across the United States, to Canada. Learn about their amazing journey and how you can help them in our storymap.
How You Can Help...
Download this guide (PDF, 1.5MB) by clicking on the image.
Monarch butterflies and their milkweed host plants have historically been common throughout California. Over the past few decades, however, monarch populations across the United States have declined. The western population is now less than 1% of its size in the 1980s.
In California, monarch butterflies overwinter along the coast, then migrate inland to spend the spring and summer breeding throughout the state, as well as other parts of the western U.S.
The Central Valley is an important part of this breeding range. This guide provides information for farmers in the Central Valley interested in adding monarch habitat to their farms.
Milkweed & Monarchs
A Guidebook for Enhancing Milkweed on Public and Private Land
Photo Credit: USFWS
Our partner, the Xerces society has produced a guide designed to help natural resource agencies and other Millkweeds and Monarchs Guuidebookland managers understand the importance of milkweed to monarch butterflies and become involved with managing, protecting and enhancing milkweed stands on their lands.
The guide also outlines how land managers can help by identifying and reporting milkweed stands and monarch breeding occurrences on their lands. download the guide here...
Monarch Migration Routes
Western monarchs gather to roost in eucalyptus, Monterey cypress, Monterey pine, and other trees in groves along the Pacific coastline of California, arriving beginning in late October. The climate of these locations is very similar to that of the Mexico overwintering locations.
The colonies generally break up slightly earlier than those in Mexico, with dispersal generally beginning in mid-February.
Less is known about the timing and location of breeding and migratory movement in the western U.S., but milkweed and nectar plant availability throughout the spring, summer and fall will benefit western monarchs, especially in California, Nevada, Idaho, and Oregon, states that appear to be important sources of western monarchs. In areas of the desert southwest, monarchs use nectar and milkweed plants throughout much of the year.
Each fall, North American monarchs east of the Rocky Mountains travel from their summer breeding grounds down to overwintering locations in Mexico. These monarchs travel up to an astonishing 3,000 miles to reach central Mexico.
There is evidence of some interchange between the eastern and western monarch populations. Perhaps this occurs when individuals cross the Rocky Mountains, when butterflies fly from the western U.S. to the Mexican wintering sites, or butterflies from the Mexican sites migrate up into the western U.S.
FieldNotes showcases the activities, events and conservation work of the U.S. Fish and Wildlife Service here in the Pacific Southwest Region. The articles inside are written by our employees and reflect the efforts of the Service and our partners in conserving and preserving the unique natural resources here in California, Nevada and the Klamath Basin. After you've visited FieldNotes, follow us on these social media channels...