Monarch butterflies that live east of the continental divide embark on a spectacular annual migration to winter roost sites in oyamel fir trees in the mountains of Michoacán, Mexico. They are the only butterflies to accomplish such a long, two-way migration each year, something more commonly associated with species like birds, wales, salmon or caribou. Unlike these other species, however, it takes three to four generations of monarchs to complete the annual migration. It is a multigenerational feat. Most monarchs only live a few weeks as adults during the migration, except for the last generation in the migratory process, the overwintering monarchs, which can live up to seven or eight months. Despite their seemingly fragile nature and their short lifespan, individual monarchs can travel hundreds to thousands of miles. Monarchs use the sun as their primary navigational tool, but according to a recently published paper in the journal Nature Communications, they are also capable of using an internal magnetic compass on cloudy days.
It is less known that monarch butterflies that live west of the continental divide, including monarchs that migrate through the Siskiyou Mountains, overwinter in various groves of trees along the central and southern California coast where they are generally protected from freezing temperatures. Monarchs aggregate in more than 25 roosting sites along the California coast each winter, but their overwintering habitat is threatened by coastal development.
According to the World Wildlife Fund (WWF), "In the most recent migration, fewer of the orange- and red-winged monarchs made it to the end of the journey than ever before. The monarch butterfly population in Mexico was the lowest ever since 1993 (the year scientists started to monitor monarch butterfly colonies), according to research just released by the WWF-Telcel Alliance and the Monarch Butterfly Biosphere Reserve Office of the Mexican government. The research shows a 43.7% decrease (nearly three acres) in the total amount of forestland occupied by monarchs in and near Mexico’s Monarch Butterfly Biosphere Reserve. The research was conducted over several weeks in December 2013 and the decrease is in relation to December 2012 research."
The WWF lists the monarch butterfly as "near threatened," or a species that is likely to qualify for a threatened category in the near future. The International Union for Conservation of Nature calls the monarch migration an endangered biological phenomenon.
|Graphic by Journey North|
Population of monarchs at the overwintering grounds in Mexico
|Monarch population chart for monarchs living west of the continental divide that overwinter in California|
In May, 2014 both Jackson and Josephine Counties in Oregon passed ballot initiatives that will ban the planting of GMO crops. The landslide victory in Jackson County shows that most people don't want GMO crops planted in Jackson County. The measure passed 65.9% Yes to 34.1% No. In Josephine County the results were 58% to 41% These two measures will greatly improve the chances of monarch recovery in the Siskiyou Mountains.
Threats to Monarch Butterflies
- Loss of milkweed
- Logging of overwintering grounds in Mexico
- Climate change
- GMO crops
- Pesticide use
- Coastal development of overwintering grounds in California
Photo essay: The lifecycle of monarch butterflies in the Siskiyou Mountains
On May 15, 2014 I spotted two monarch butterflies fluttering around two separate showy milkweed (Asclepias speciosa) patches that my wife, Suzie, planted nine years ago. One patch is in our vegetable garden and the other in a native rock garden on the side of the road. Previously we had only seen one tattered monarch scoping out our patches, so this was a hopeful sign. When Suzie got home from work that day I told her what I saw and she immediately inspected for eggs. Sure enough, there were about fifty eggs combined on both the patches of milkweed. Research has shown that a female monarch typically lays about 700 eggs in its lifespan, so this was not a huge number of eggs.
|Monarch caterpillar eggs on milkweed|
|Monarch caterpillar eggs are very small|
|Monarch caterpillars are tiny and vulnerable when they first emerge.|
Around ten days later the eggs started to hatch and an estimated 15-20 tiny, little caterpillars emerged. They were hard to spot because they hid within the plants and it was hard to keep track of them and know for certain how many there were.
|When small the caterpillars stayed within flower buds.|
|The caterpillars eat the milkweed plant and grow bigger.|
The tiny caterpillars got bigger as they ate the milkweed plant, mostly staying within the protection of the flower buds. They never denuded the plants, but rather took little chunks out here and there, allowing for the viability and sustainability of their host plant.
|As they get bigger they are easier to spot.|
|Sometimes they eat the flower buds.|
|Some small caterpillars died of mysterious causes.|
Over the course of a few weeks a number of caterpillars disappeared, but those that remained got bigger and fatter. Monarchs have natural predators, parasitoids, and parasites that can harm monarch eggs, larvae, pupae, and adults. It's a tough world for monarchs in their natural setting, and human impacts to habitat just compound the threats.
In just two weeks a caterpillar will grow and need to shed its skin five times. Each skin is called an instar. The stages of a caterpillar's life are referred to as the first instar, second instar, third instar, fourth instar, and the final fifth instar. We observed the caterpillars eating the skin after it was shed, as if it was a source of nutrition.
|Hanging out on milkweed|
|Munching on milkweed|
|The caterpillars rested under the leaves|
|5th instar caterpillar|
|Monarch caterpillar hanging in "J" shape on June 23, 2014.|
The caterpillar has attached itself with a cremaster and hangs in a "J" shape as it prepares to shed its old larval skin and begin the formation of the chrysalis.
|Monarch in a chrysalis formed on June 24, 2014.
The scientific name for the monarch butterfly is Danaus plexippus, a Greek term meaning "sleepy transformation." This reflects the species' metamorphosis.
|Monarch on showy milkweed in May, 2014|
After its metamorphosis into a butterfly the monarch will eat, mate and lay eggs if it is a female. They will search out and find whatever milkweed they can. Monarchs will use any plant in the genus Asclepias, even cultivars of the native species. The last generation in the migration will then head south to the California coast to overwinter and start the cycle anew as has happened for millennia.
Monarchs fall to the ground while mating. This photo was taken at the end of January at the Pismo Beach Monarch Butterfly Grove in California.
|Monarch butterflies cluster together for warmth as
they overwinter at the Pismo Beach Monarch Butterfly Grove in
California. This colony is one of the largest in the United States.|
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