Why monarch butterflies migrate

As they migrate southwards, Monarchs stop to nectar, and they actually gain weight during the trip! Some researchers think that Monarchs conserve their "fuel" in flight by gliding on air currents as they travel south.

This is an area of great interest for researchers; there are many unanswered questions about how these small organisms are able to travel so far.

Another unsolved mystery is how Monarchs find the overwintering sites each year. Somehow they know their way, even though the butterflies returning to Mexico or California each fall are the great-great-grandchildren of the butterflies that left the previous spring. No one knows exactly how their homing system works; it is another of the many unanswered questions in the butterfly world. We have created a comprehensive map representing both the fall and spring migrations both east and west of the Rocky Mountains.

To the extent possible, the map is based on data. Nevertheless, our knowledge of the distribution and abundance of monarchs in some seasons is lacking for certain areas of the country. In these cases, our interpretations are based on what monarchs are doing in surrounding areas. Monarchs east of the Rocky Mountains fly south to the forests high in the mountains of Mexico — roughly 40 percent of all monarch butterflies that overwinter in Mexico come from Iowa and other Midwestern states.

And those west of the Rocky Mountains travel to small groves of trees along the California coast. More: Des Moines Parks hosts monarch butterfly tagging events as part of a community science project.

Monarchs live in other places in the world, but the North American populations are the only butterflies to travel so far — up to 3, miles — and participate in a two-way migration lasting several months. Flight food: Shorter days and cooler temperatures trigger the migratory state of the monarchs.

They travel south, feeding on on nectar and water attracted by flowers such as purple aster, thistle and tickseed sunflower. More: Iowa farmers play crucial role in monarch butterflies' survival. Following the sun: Monarchs use the sun, and probably the earth's magnetic field, to find their way south. But an unknown instinct leads them to the same location year after year, although they are the great-great-grandchildren of the butterflies that left the previous spring.

They take advantage of high air currents, which allow them to soar like birds and often travel miles a day. Most monarch butterflies that emerge after about mid-August in the eastern U. From across the eastern U.

Along the way, they find refuge in stopover sights with abundant nectar sources and shelter from harsh weather.

Upon reaching their destination in central Mexico beginning in early November, monarchs aggregate in oyamel fir trees on south-southwest facing mountain slopes. These locations provide cool temperatures, water, and adequate shelter to protect them from predators and allow them to conserve enough energy to survive winter. In March, this generation begins the journey north into Texas and southern states, laying eggs and nectaring as they migrate and breed. The first generation offspring from the overwintering population continue the journey from the southern U.

Second and third generations populate the breeding grounds throughout the summer. It is generally the fourth generation that begins where we started this paragraph, migrating through the central and southern U. 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 US, 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. For western monarch information and resources, visit the Western Monarchs category of our Downloads and Links page.

Many of those who do migrate fail to complete migration. Some are blown off course and land in places they never intended to go. Some migrate only far enough to find warm temperatures; these individuals may or may not go into hibernation, and may or may not survive the winter, in places like Tennessee or Florida.

Probably a few Monarchs hibernated in Virginia long before Virginia received its current name. Descriptions of animal migration behavior based on what the most successful individuals do, so they will not accurately describe every single butterfly you see flying south in October.

For many years, the main dangers were to individual butterflies. Some butterflies who attempted migration might simply have been too old when they started the journey. Some were eaten by birds or struck by cars. Some might have stopped for a sip of nectar from a freshly sprayed flower. And almost every year, somebody found a stray Monarch who had obviously been trying to get to Mexico spending the winter in some part of Britain, instead. Today, habitat changes are putting some Monarch populations on locally endangered species lists.

Monarch Butterfly extinction has become something people can imagine. It is important to understand that all of the contiguous United States, most of Canada below the Shield, and most of Mexico are Monarch Butterfly habitat for at least part of the year. Variations from year to year have been nothing to worry about.