Millions of monarch butterflies arrive in the forests of central Mexico every year in November where they migrate to survive the winter. At least that’s what is supposed to happen.
Decreasing populations
Continuous loss of habitat, farming with herbicides and bouts of severe weather have depleted the population of monarchs. The World Wildlife Fund estimates that there were only about 33 million monarchs accounted for in 2013, down from 201 million in 2010.
The Associated Press reported Jan. 29 that scientists fear the migration is in danger of disappearing altogether as they reported the lowest number of Monarchs in Mexico since record-keeping began in 1993.
Monarchs in a colony hang in layers thus making it hard to count an actual number, but it is estimated that there are 50 million monarchs per hectare in a colony.
Every winter, scientists visit the butterfly sanctuaries and measure the area covered by Monarchs. The decreasing numbers over the past 10 years are alarming.
Jenn Tremeer, the resident Monarch expert at the Cambridge Butterfly Conservatory suggests that the main reason for the decline in population of Monarch butterflies in North America is loss of habitat.
“There were many fields that used to grow milkweed and that is being destroyed by the spraying of chemicals,” said Tremeer. She says that in the US, it is estimated that 120 million acres of habitat has been lost. Milkweed is important to the Monarch because they breed only where milkweed is found. The pesticides are destroying their breeding grounds.
“There is definitely a connection with the decreasing population of bees,” said Tremeer. “The use of pesticides is the main factor”.
The Cambridge Butterfly Conservatory is trying to raise awareness of the decreasing population of Monarchs. To do this, they have education programs that 10, 000 students take part in along with conservation experts.
One important program is the Monarch tagging weekend. This year, it will take place on Sept. 13 and 14, 2014.
“This can only be done in the fall,” says Jenn. “Monarch kits help share the experience of raising and tagging Monarch butterflies.”
During Monarch tagging weekend, participants can view migration exhibits that explain the journey that the butterflies make every fall. They learn how to save Monarchs as well how to attract them to your their own gardens.
Participants tag their butterflies before they release them and track their journey to Mexico.
Monarch migration
Monarch butterflies from Canada as well as most of the United States migrate south and west each autumn to escape the cold weather. The Monarch migration usually starts in about October.
The monarch butterflies will spend their winter hibernation in Mexico and some parts of Southern California where it is warm all year long.
If the Monarch lives east of the Rocky Mountains, it will migrate to Mexico and hibernate in Oyamel fir trees. If the monarch butterfly lives west of the Rocky Mountains, it will hibernate in and around Pacific Grove, California in eucalyptus trees.
Monarch butterflies return to the same trees other Monarchs used the year before. Monarch butterflies are the only insects that migrate to a warmer climate that is 2,500 miles away each year.
The Monarch butterfly migrates for two reasons:
-They cannot withstand freezing weather in the northern and central continental climates in the winter
-The larval food plants do not grow in their winter overwintering sites
Thus, the spring generation must fly back north to places where there are many plants. The map below shows the migration route of the Monarch butterfly.
(source: Canadian Geographic)
Monarchs typically arrive in Mexico around Nov. 1 and return to North America by June. In 2013, Monarchs were not seen in North America until mid-July.
Help for Monarchs
The monarchs’ winter sanctuaries in Mexico are threatened by logging activities and other deforestation. The Monarch Butterfly Sanctuary Foundation was created to aid in the survival of these butterflies.
Even a small planting of milkweed for Monarch caterpillars and flowers with the adults’ favourite nectar will attract Monarchs and allow them to grow, like this one (run mouse over image below).
This photo gallery shows more in depth information on the migration cycle as well as life cycle of Monarch butterflies.
