BirdCapeMay.org

Millions of Monarch butterflies pass through Cape May each autumn on a migratory journey. Weighing just ½ gram, they must successfully navigate a journey of over 2,000 miles to the forested mountains of central Mexico. Many perish along the way. Once in Mexico, these seemingly fragile butterflies while away the winter, waiting for spring to return to the U.S. and Canada. On some unknown cue in March, they break dormancy and head north, mating along the way. Females lay their eggs on milkweed plants growing in northern Mexico or the extreme southern U.S. Their offspring repopulate much of temperate North America where two or three non-migrating generation occur during the warmer months. Then in autumn, the migration begins again, with Monarchs heading to the same areas where their great-great grandparents spent the previous winter.

The incredible journey of migratory monarchs is threatened by human changes to the environment. In Mexico, illegal logging at the monarch reserves shrinks the size of their sanctuary and reduces the forest’s ability to buffer the butterflies from weather extremes. In the U.S., pesticides and genetically modified corn plants can cause significant mortality to the monarchs. Habitat loss, at breeding sites and key migration stopover points, can also impact monarch populations.

Much is still unknown about how monarchs are able to make their great migratory journeys. Researchers at Cape May are working to monitor numbers of migrating monarchs and to learn about how varying environmental factors influence their migration. A standardized census count is made three times each day between September 1 and October 31. Censuses were first begun in 1991, making our project the longest continuous quantitative study of migrating monarchs in the world.

Thousands of monarch butterflies are tagged each year in Cape May. The tags are small bits of coded adhesive paper placed on the leading edge of a monarch’s wing. The tags don’t change the way the monarchs behave or fly. Dozens of monarchs tagged in Cape May have been found in Mexico. Additionally, tagged monarchs are sometimes caught again at areas to our south, providing valuable data about the speed and routes of the migration. One monarch tagged at Cape May was found the next day at Fisherman Island, in the mouth of the Chesapeake Bay in Virginia – about 140 miles from Cape May!

Our work doesn’t end with research. Talks about monarch biology and demonstrations of the tagging technique are offered frequently during the monarch migration season. Check with the Cape May Bird Observatory for the schedule.

You can learn more about monarch butterflies and help support our research by adopting a tagged monarch butterfly. In exchange for a minimum contribution of $25, you will receive a certificate with the tagging details of the monarch you adopt. If that monarch is found again, either in Mexico or at some spot along the way, you’ll receive another certificate that chronicles the journey of your special butterfly.

You can adopt a monarch in your name, in the name of a friend or relative, in honor of a special occasion, or for a school class or club. All contributions will be used solely to support the monarch monitoring project.