Dots on Monarch Butterflies

We went to a lecture given by a Cal Poly grad student. She is studying and tagging Monarchs in our area and we went with her one morning as she did a count. Look close and you will see two butterflies in this picture with yellow dots. The yellow tags tell us at what location it was tagged and has other information. There are about half a dozen clustering sites around here with Pismo Beach being the largest. I would love to go with them to do some tagging. It is done in the early morning, the colder the better. There are very long handled butterfly nets and brown paper bags involved.

The students are gathering information on how the individuals in a cluster move about and how far they might go to nectar. We see many Monarchs in our back yard but have so far not found a cluster site on our property. They do love to nectar on our Lantana and I am watching for those tags. If I saw a yellow tagged butterfly in our yard that would mean it had traveled about four miles from the site where it was tagged. We did find a small cluster site about a mile from us that the students had not known about.

The Western Monarchs travel from Washington, Oregon and Nevada and arrive in our area around early October. Some clusters go south as far as San Diego. They do not go down into Mexico. Those are the Eastern Monarchs. The Western Monarchs are here until February or March and then they mate before they start their journey back to the north. It takes them about three generations, each living around 6-8 weeks to get back. They lay their eggs on Milkweed with the first eggs being laid in the central California valley and the Sierra foothills. Then the new generation travels north staying on the western side of the Rockies. An abundance of Milkweed seems to help trigger the laying of more eggs and a new generation to continue on to their summer sites. It is interesting to note that the migration south in the fall is made by one generation and they live for about 6 months. The same butterflies make that whole long trip... they must catch a tail wind!

Monarch numbers are declining. There are good years and bad but over all the numbers are going down. They seem to prefer Eucalyptus trees for clustering in our area, although Pines or Cypress are used too. The Eucalyptus trees bloom in January and February and provide nectar as well as a roosting place. Many people are cutting down the Eucalyptus trees around here. Has that contributed to the decline of the Monarchs? They are not native trees and many groups would like to remove them all.

But that is another story for another time.