Monarch Butterfly Migration Update: March 18, 1997
Dr. Stephan BuchmannAdios Angangueo! The monarchs are clearly on the move according to the two latest reports from Mexico. We hope to have news next week about the progress of the symbolic migration. Meanwhile, more monarch have been sighted in Texas. Here are the reports from Fernando and Benigno, and the location of latest monarch sightings:
* Thanks to Monarch Watch for providing these sightings!
How to REPORT:
Dr. Karen Oberhauser has returned from the Mexican wintering sites and filed a report today. "The trip renewed our sense that the migration of the eastern North American population of monarch butterflies is the most amazing biological phenomenon in the world. Our trip was full of incredible biology, wonderful people, good weather, hard work, and a conviction that it will take many years to fully understand everything we observed." Also conducted research at the time was Dr. Lincoln Brower. This was his 20th trip to the monarch sanctuaries in Mexico! Both scientists worked to answer important questions about monarch biology--and issues related to their conservation. After you read Dr. Oberhauser's report, see if you can answer these Challenge Questions:
Challenge Question #6
Challenge Question #7
To respond to these Challenge Questions, please follow the instructions at the end of this report.
Dr. Brower with butterfly he sent on the symbolic migrationIn our February 25th report we explained that Dr. Brower uses an analogy to describe the monarchs winter habitat: We asked you to consider Challenge Question #3: "How does the pine forest serve as an umbrella and a blanket for the monarchs?"
Lee Taylor and Shannon Mitchell in Bobcaygeon, Ontario (firstname.lastname@example.org) said, "The pine trees serve as an umbrella because they keep rain from pouring down on the butterflies and soaking their wings. They serve as a blanket because they keep the warmth in at night. If they cut the trees down, they put a hole in the blanket and the monarchs will freeze to death."
Students in Kwajalein, Marshall Islands (email@example.com) also figured the monarchs use pine trees as a blanket for insulation and as an umbrella for shelter from weather. In fact, according to Dr. Brower's research, it is the combination of these 2 factors that is especially important. He discovered that wet butterflies freeze much more easily than do dry butterflies. For example, when butterflies were wet and exposed (not protected by the trees) they froze to death when temperatures dropped to -0.5 C. In contrast, when butterflies were dry and insulated by the pine trees they could withstand temperatures as cold as -8 C. The thinner the forest, the more easily cold temperatures affected the safety of the butterflies. This is one of the most important conservation issues for monarchs in Mexico, because the people who own these forests want to use the trees as a source of income. How do you think the controversy can be resolved?
In our last report we asked Challenge Question #4: "How do you think monarchs know when it's time to leave Mexico? (That is, how do you think the butterflies 'tell time'?)"
Students put a lot of thought into this question--and scientists have too! Click Here to see their answers. Students at Fredstrom Elementary in Lincoln, Nebraska explain the sequence of events this way:
"We think that when the days get warmer and longer the butterflies will feel like mating. Once they have mated they will want to come back north to lay eggs. Then they die after they've laid their eggs. Then the cycle begins all over again. Next year they will be migrating back to Mexico. The weather is getting warmer and the sun is out longer, so the days are longer. The flowers start blooming. The monarchs have instincts to leave Mexico and start flying north. The females are mating, then are looking for milkweed. Since they can't fly in cold weather, they must wait until the weather is warmer. They left in the fall because northern winters are too cold." Mrs. Siefert's & Mrs. Thornton's
Just as the students thought, photoperiod and temperature are the two environmental factors which are believed to trigger renewed activity in the colonies, leading up to their migration. As you have read in field reports from Mexico, by late February and early March activity had increased dramatically. Also during this time the butterflies' sexual organs finally matured. (Remember, these organs had been state of arrested development since late last summer.) How this all works is still a mystery. In fact, it is being studied this very moment! As Dr. Oberhauser's report describes, graduate student Liz Goering is currently using monarchs collected in Mexico to study how mating and access to host plants affect the timing of female diapause termination. ("Diapoause" is the non-reproductive, hibernation-like state in which monarchs overwinter.)
By the way, many students said monarchs know when it's time to leave by "instinct". This is of course true. Any behavior that is not learned can only be explained by instinct. Since these monarchs were not alive last spring, their behavior cannot have been learned. Monarchs know when to leave Mexico in the spring because the information is passed from generation to generation through their genes.
Respond to Today's Challenge Questions:
How to Respond to Journey North Monarch Challenge Question # 6
Challenge Question #6
How to Respond to Journey North Monarch Challenge Question # 7
Challenge Question #7
The Next Monarch Migration Update Will be Posted on March 25, 1997.