Monarchs Move South
(This column was first published in the November 12, 2001 Buffalo News.)
Most readers are familiar with bird banding, an activity first practiced by the famous artist, John James Audubon. By ringing the legs of a nesting family of phoebes with tiny wires, Audubon was able to prove that the same birds returned the following year. What the 19th century ornithologist started is now practiced by thousands of banders worldwide.
Probably far fewer realize that entomologists mark monarch butterflies to study their migration too -- not, of course, with leg bands but with tiny circular tags on their forewings. For many years this was done almost exclusively by Fred and Norah Urquhart and his University of Toronto students, giving the study of these lovely insects a kind of regional character. More recently, however, records have been kept by the Entomology Department of the University of Kansas in Lawrence.
Although the total number of monarchs marked each year does not approach the number of birds banded, administrators of the "Monarch Watch" program estimate that over 76,000 were marked in 1999, the most recent year for which data is available. Most of those butterflies were tagged by schoolchildren who participate in the project.
Remarkably, over 850 of those marked were recovered. That is a recovery rate of better than one out of 90, which may not seem so great until you realize that about a half-billion monarchs fly south each fall. If you have a calculator handy, you can do the arithmetic -- 500,000,000/76,000 -- to show that only one out of about 6500 butterflies that we see fluttering by toward the south is marked. Finding one seems like looking for a proverbial needle in a haystack.
Why then were so many found? (Those of you who know something about monarch migration should be able to work out the answer. Stop here for a moment to do so before reading on to check your solution.)
A quick look at the records of marked butterflies that are found gives away the answer. Very few of the 1999 returns are from the United States -- only 62 in fact. Almost all of the rest are from a small area in the Transvolcanic Mountains west of Mexico City.
So many millions of monarchs gather there each winter that you cannot see the trees and ground. The covering looks like orange and black kudzu but instead it turns out to be butterflies. More spectacular still: there are so many that you can even hear a general noise made by the fluttering of their delicate wings.
It is there, of course, that scientists and volunteers can find so many of those marked individuals.
The data provide other interesting information as well. I noticed one monarch that was banded near Ithaca, New York and was recaptured in Virginia eight days later. In that time it had traveled 192 miles. If it flew ten hours a day, more arithmetic shows that it maintained an average speed of 2.4 miles per hour, about as fast as I hike -- but rare is the day I can do so for ten hours. How remarkable for such a delicate insect.
To learn more about monarch butterflies you should attend the two Distinguished Lectures at the Buffalo Museum of Science this weekend. Professor Lincoln Brower of Sweet Briar College and the University of Florida will speak Friday at 7:30 p.m. The title of his talk is "The Grand Saga of the Monarch Butterfly: Migration, Overwintering and Conservation Biology". Then the following evening at the same time his topic is "Of Monarchs, Mice and Milkweeds: a Co-evolutionary Arms Race." These lectures will draw upon his over 20 years of field and laboratory research.-- Gerry Rising