Skip to Content
Frequently Asked Questions
Wendy caldwell ducks 6 30 077

Migration

Is the monarch migration tracked by placing transmitters on the migrating adults?

The tracking of monarch movement across the country has been done by placing ‘tags’ or stickers marked with a unique 6-character identification code and the name and contact information of the organization the tag belongs to. When a monarch is captured or seen passing through an area the ID code and other information are recorded and submitted to the organization who conducted the tagging. Find out more about tagging programs here.

In September 2023, Cape May Point Science Center and Cellular Tracking Technologies deployed the first ever solar-powered coded digital radio tags on monarchs this week in Cape May Point, NJ. These tags weigh 0.06g and have no battery, so as long as they have sun on them, they will transmit their unique ID once per second. Since they operate on the same frequency as Bluetooth, they can be detected by any smart device running the Project Monarch Science app (with a ~100-200m range from cellphone to tag). The free Project Monarch Science app means YOU can download data and YOU can be a part of the research, logging your sightings and contributing to community science!

The app is available in both iOS and Android app stores:

Project Monarch Science- iOS
Project Monarch Science- Android

Are the tags used for tracking butterfly movement harmful to the butterflies?

If carefully placed on the wings of the butterfly and in the correct location, the tags used to track monarchs are not harmful. According to protocol, tags should be placed over the discal cell on the hindwing (visit monarchwatch.org for images and details) to prevent interference with flight.

How many miles can a monarch fly in one day?

In general, about 25-30 miles. When weather conditions are favorable, they may be able to go further, but poor weather conditions may also prevent them from traveling at all! Many factors influence how far monarchs can travel in one day, so it is quite variable.

What dangers do monarchs face on their migration?

The long migration comes with many dangers. Monarchs rely on good weather to help them make progress in the right direction; strong winds and rains may prevent them from moving, holding them up for days on end. If winds are too strong in one direction, monarchs may not be able to travel as far, if at all. Another weather factor that can impact monarch travel is temperature. If late season temperatures get too cold, monarchs' flight muscles can't warm up enough, making it physically impossible for them to fly. Extreme weather events can blow monarchs off course, prevent them from moving forward, or kill them.

Monarchs also require nectar to fuel their flight during the migration. If they are unable to find suitable nectar sources throughout their migratory path, they may die of starvation. They may make it to overwintering grounds, but sometimes they are undernourished when they arrive and could not store enough lipids/fats to survive the winter. It is important that they have access to abundant nectar sources along the way.

Disease can impact the monarch migration. The OE parasite can have a culling effect, meaning that monarchs infected with the parasite may not be strong enough to complete the migration and die on their way.

Other anthropogenic factors, like collisions with vehicles, also pose dangers for migrating monarchs.  

How do monarchs travel such far distances?

Monarchs are able to travel such far distances because they fly very efficiently. They take advantage of air currents and actually soar, like many birds do. This takes much less energy than flapping their wings all the time. They choose altitudes at which they can take advantage of the wind to help them on their long migratory flights. And they don't fly when there's a strong wind blowing in the wrong direction. They also store up a lot of energy for these long trips. This energy comes from the food they eat as caterpillars, and also from the nectar they get from flowers.

When do monarchs arrive in Mexico and when do they leave?

Typically, monarchs arrive in Mexico around the same time as the Day of the Dead in early November. They spend the winter in the Mexican overwintering sites and then the colonies start to break up and migrate back towards the U.S. starting in March

How far north can a 4th generation adult monarch return in the spring?

The 4th generation reaches the northern part of their range. They can be as far north as Maine, Minnesota, and Canada!  For more information, visit the Monarch Lab site.

How can I tell if late eggs/larvae are part of the reproductive or migratory generation?

In short, the fall migratory generation isn't cleanly divided from the later summer breeding population. If a butterfly is reproductive, it won't successfully migrate and overwinter because reproduction requires a huge investment of their body/lipid reserves, so they don't live as long once reproductive. Reproductive diapause is when monarch's reproductive organs are delayed in maturing - they wait until the next spring at their overwintering grounds. Once their reproduction organs mature, they'll continue to lay eggs on milkweed until they die. This doesn't bode well for a window of late-season eggs/larvae with limited success in fully developing and completing the migration. That said, the 'pre-migration' phenomenon does show that reproductive monarchs are moving south and continuing to lay eggs. This doesn't mean they'll make it to Mexico and survive the winter. Because the last of the reproductive butterflies from July/August continue to lay eggs until their death, and the migratory butterflies are emerging at the same time, there is no exact time that all butterflies you see are either one or the other (reproductive or migratory).

Should I ship monarchs south (or take them with me on vacation to release) in order to help them on their migration?

We do not recommend moving monarchs (USDA permits are required to ship across state lines). There are many naturally occurring factors that lead to late-season monarchs that will not survive the winter. This is part of the natural cycle of life for thousands of organisms across earth's ecosystems. Because monarchs rely on a combination of environmental cues to sustain their migration, we discourage interference with natural conditions. Motivation is high to help protect monarchs and their migration. We support everyone's enthusiasm for helping monarchs! We highly recommend planting monarch habitat and participating in community science as two primary ways to help protect this valuable species. Please check out our educational handouts for more information on many dimensions of monarch and pollinator conservation.

How can I track the monarch migration?

Since Fred Urquhart’s tagging success, researchers and community scientists have continued tracking the migration by reporting their observations of migrating monarchs and tagging.

  • Journey North: This simple, online reporting project engages thousands of children and adults. Volunteers report sightings during the spring and fall migrations through the project’s website. Data are aggregated and used to develop real-time maps of spring and fall migration fronts.

  • Monarch Watch: With over 1 million butterflies tagged and approximately 16,000 recovered tags, the Monarch Watch volunteer tagging program helps us understand the eastern monarch fall migration to Mexico. Tagging and recovery data  provide information on the dynamics of the migration. Volunteers order circular, lightweight stickers that they place carefully on the wings of monarchs. A unique ID number on each tag is used to keep track of information associated with each butterfly, tagger, and recovery.

Many smaller, more localized, community science programs have been implemented throughout the country, including:

  • Southwest Monarch Study: Based in the desert southwest, this program provides both tagging and monitoring of monarch habitats in Arizona, New Mexico, Nevada, Utah, western Colorado and the California deserts. Data collected from this project help us to understand the migration, breeding, and overwintering strategies of monarchs in the southwest U.S.

  • Programs like the Cape May Migration Monitoring Project (New Jersey) and the Peninsula Point Migration Monitoring Project (Michigan) conduct regimented counts of all monarchs they see during a fixed period of time. These, and many other local monitoring programs, are vital sources of information about the state of the monarch migration and population in varying locations.

Learn more about tracking the monarch migration, breeding and overwintering with monarch community science here.

How far can monarchs fly?

Every fall, North American monarchs fly south to spend the winter at roosting sites in Central Mexico or along the Pacific Coast. Monarchs are the only butterflies to make such a long, two-way migration. Eastern monarchs may fly up to 3000 miles in the fall to reach their winter destination if they are coming from the far northern part of the eastern breeding range. If they are coming from a more southern area of the breeding range, they will have fewer miles to go.

Less is known about the timing and location of breeding and migratory movement in the western U.S. Usually, monarchs coming from west of the Rockies make a shorter journey to the coast of California. In some cases, western monarchs have been documented to fly long distances to Mexico rather than to closer sites in California!

During migration, monarchs will fly about 25-30 miles per day in general. When weather conditions are favorable, they may be able to go further, but poor weather conditions may also prevent them from traveling at all! Many factors influence how far monarchs can travel in one day, so it is quite variable.

You can help document the migration of monarchs wherever you live by contributing to monarch community science!

To learn more about monarch migration, visit our migration page, Journey North, or the Southwest Monarch Study.

Is the monarch migration at risk of extinction?

A recent publication indicates substantial probability for “quasi-extinction” of the Eastern monarch butterfly migratory population within 20 years if ambitious habitat restoration and conservation goals are not achieved. Quasi-extinction means that the population reaches levels that are so low that it would be unlikely to recover. To minimize this risk, national population targets have been set to restore the Eastern monarch overwintering population size to 6 hectares of space occupied in Mexico through the addition of habitat across North America, including about 1.5 billion additional milkweed stems. Achieving this population size may help the population rebound more readily after stochastic weather events, such as the major winter storm that occurred in the late winter/early spring 2016 at the overwintering sites in Mexico, which likely caused significant mortality of the butterflies remaining there. Read more here.

Do monarchs return to the same areas when they are traveling north?

There is no evidence to suggest that an individual monarch’s offspring return annually to the habitats their ancestors came from. It is most likely that the monarchs you see each year are new to your garden, and not the same monarchs that grew there previously, or their descendants. This is because there are 4 generations that take place throughout the year for eastern monarchs. By the time monarchs are back in the summer breeding range the next year, they are generations removed from the breeding individuals of the previous year. 

During the eastern population’s summer breeding season, 3 generations pass before the migratory generation (the 4th generation) leaves for Mexico. Successful migrating monarchs will live between 6 to 9 months and reproduce and die in the southern U.S. in the spring. Their offspring then carry on their migration north. Therefore, individual monarchs do not make it back to their original starting place. For a visual reference of the monarch generations click here. 

Are the western and eastern populations genetically isolated, or do they sometimes mix during migration?

The eastern and western monarch populations are not genetically different. The eastern population refers to the monarchs that overwinter in Mexico, and the western population refers to the monarchs that overwinter along the Pacific Coast. There is evidence of interchange between the eastern and western populations, perhaps 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 fly into the western U.S. Learn more about monarch migration on the biology page of our website.

What information is available about offshore islands as stopover habitats during migration?

Read more on this topic in an article written by Monarch Watch Conservation Specialist Candy Sarikonda. In addition, there is a Monarch Migration community science app that has been developed to help capture these reports and provide additional insight.

How many generations does the western monarch population see annually?

Typically the western population sees 4 generations, the same as the eastern population. They usually break up from the overwintering sites in California in mid-February and arrive beginning late October.

Why are monarchs in southern Florida non-migratory?

A warmer climate and the continuous availability of milkweed (for larvae/breeding) and nectar (for adults) allow monarchs to persist and breed year-round in southern Florida. The extent to which there is interchange between the south Florida population and the eastern population during migration seasons is unknown.