Monarch Butterfly Migration Update: September 3, 2004
Today’s Update Includes
Highlights From the Migration Trail
In the north,
everybody is commenting about the lackluster migration. There have been
no reports of large aggregations or of large numbers in flight. Let’s
see if numbers rise during the next week.
states, monarchs are not typically seen in the summer until late-August.
As if on cue, during the last 10 days we received reports of first monarchs
spontaneously from Arkansas, Oklahoma, North Carolina, South Carolina,
Georgia, Virginia, Kansas and Texas.
How Many Monarchs in Mexico This Winter? Dr. Taylor Predicts
to Dr. Chip Taylor of Monarch Watch, "Late summer reproduction in
the south, especially in Texas, could contribute more butterflies than
normal to the migration due to well-distributed rainfall. Overall, the
wintering population should be in the range of 4-6 hectares."
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This Week’s Migration Focus: The Overnight Roost
Monarch butterflies only migrate during the day. At night, they come down to rest. They spend the night in trees, clustered together in “roosts” or “bivouacs.”
In the morning, the butterflies must warm up before they can fly. Monarchs cannot even crawl when their thoracic temperatures are below 5C (41F). To fly WELL, with lots of control, they need to attain thoracic temperatures in the upper 20’s or even 30’s C. Outdoor temperatures drop as the fall season progresses, so monarchs have a shorter and shorter window of time each day in which they can fly. This is one reason monarchs must leave the north before it gets too cold!
Year after year, people often see monarchs at the same roosts along the migration trail. Where do these roosts tend to form? Do the monarchs find them by scent? Here Dr. Bill Calvert clears up some misconceptions:
Roost: Five Monarchs Instead of Thousands
The graph on the left shows the number of butterflies as of September 1 each year from 2001-2004. Do Mr. Viger’s data correlate with the data Dr. Oberhauser collected this summer in the Upper Midwest? (See graph on the right.)
At any overnight roost, the number of visiting monarchs tends to rise and fall from one night to the next. Take a look at the data Mr. Viger collected during the Fall 2001 season. What relationship do you see between weather and migration? Why do you think monarchs behave this way?
If you discover a monarch roost, how would you count the butterflies? Here is a chance to practice. Scientists often use photographs to estimate numbers, whether they are counting whales or caribou, bats or butterflies. How many monarchs are in these pictures?
Reminder: Symbolic Migration Deadline Oct 15
Only 42 more butterfly-making days before the Symbolic Migration deadline. Don't be late! Butterflies received after the postmarked deadline cannot migrate.
Please Support Monarch Conservation in Mexico!
The forest sanctuaries in Mexico are not adequately protected. Logging and other development threaten the habitat monarchs need to survive the winter. Please send support for the real butterflies with your symbolic monarchs!
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The Next Monarch Migration Update Will Be Posted on September 10, 2004.
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