DETROIT (AP) - Habitat loss and an especially harsh winter are proving to be a destructive combination for Michigan's monarch butterflies, though locally the monarch population may have improved from last year.
The cold weather affected the monarchs' migration north, causing them to arrive in Michigan later than usual, according to Diane Pruden of Milford Township, a citizen researcher for Monarch Watch, a nonprofit education, conservation and research program based at the University of Kansas.
Because of their late arrival, butterflies are laying eggs later and in lower numbers this year than Michigan has seen in the past, the Detroit Free Press reported. Monarchs are usually spotted around the state in May and June, but Pruden said she only recently saw eggs for the first time this season.
Holly Richer | Daily Press
A monarch butterfly lands on a rock at the Escanaba Harbor. Experts say this summer’s cool temperatures have impacted monarchs and their annual migration.
Locally, however, the monarch population seems to be better than last year, said Sue Jamison, coordinator for the Monarch Larva Monitoring Project at Peninsula Point on the Stonington Peninsula, a project she has been involved in for nearly 12 years.
Through the project, a team of two people monitors two fields located about a mile before the lighthouse on Peninsula Point each Wednesday.
"This year seems to be better than last year as far as the number of eggs and larva (caterpillars) are concerned," she said. "We are finding more larva and eggs even though it seems there are not as many monarchs flying around."
When monitoring larvae, volunteers use a random compass point in the field and walk a shoulder width path counting milkweed plants and checking for eggs and larva. The data collected each week is sent to the University of Minnesota along with data collected from other monitoring sites around the United States. Monarchs are monitored from the end of May to the end of September.
Stonington is unique due to its large concentration of monarchs, said Jamison.
"When the monarchs from here are ready to migrate south they are faced with a barrier of Lake Michigan," she said. "Since they do not like to fly over large bodies of water they will follow the shoreline until they get to the tip of the Stonington Peninsula. From there they will fly the short distance over the lake. Peninsula Point also has many cedar trees which shelter the resting monarchs from the wind."
Jamison also highlighted four factors, which seem to affect the monarch population. The first is attributed to their winter habitats in Mexico, which are in danger from the logging industry there. Though the Mexican government has tried to prevent logging in the monarchs' habitat areas, illegal logging still occurs.
Another factor is the drought in Texas, where monarchs have less nectar to fuel up on due to drought conditions when passing through the state.
Farming in the Midwest has also played a role.
"Eliminating the wild growth around fields and using herbicides to kill areas of growth around fields has eliminated many milkweed plants," said Jamison, noting that milkweed plants are the only food source for the larva of monarch butterflies.
This ties into a fourth factor, the cutting down of median strips along highways as well as wild growth on the sides of highways, which eliminates milkweed plants.
Because of this, Jamison urges people locally to plant milkweed in their yards and on their property or to talk to highway departments about leaving large areas of milkweed untouched on highways. Flower gardens are also helpful for adult monarchs as they provide nectar, which is their primary food source.
Elsewhere, Orley Taylor, the founder and director of Monarch Watch, said the monarch population has been on the decline for about 10 years. But he said it reached an all-time low this past winter.
"There's a great deal of concern that the monarch migration is on the verge of collapse," he said.
He said much of the land in the central plains states where milkweed once prospered has been repurposed for corn crops. According to U.S. Department of Agriculture statistics, nearly 23.7 million acres of grassland, wetlands and shrub lands were converted to agriculture in this area between 2008 and 2011.
The monarch is one of a few migratory butterflies. It travels up to 4,000 miles to Mexico every fall. The butterflies that return to Michigan are the offspring of monarchs that lay eggs in Texas and Oklahoma before dying off.