Marvelous Migrating Monarchs
By Sue Corcoran
H
ow to track a butterfly? Even as a child
Fred Urquhart puzzled over this. They are
too small to band and too fast to follow.
Young Fred, like other curious observers,
could only guess where butterflies went when he didn’t see
them. Then in the 1930s Fred, who had become a biology
professor at the University of Toronto, began to experiment
with tagging monarch butterflies (Danaus plexippus). Hoping
to learn where these beautiful insects go when they leave
Canada toward the end of summer, he found tiny tags applied
to the wings did not interfere with their flight. Forty years
and thousands of tags later one bearing a small white disc was
reported high in the mountains of a remote area of Mexico
hibernating amidst millions of monarchs. This stunning
discovery was the cover story in the August 1976 issue of
National Geographic magazine
The monarch, king of butterflies, is aptly named because
of its size. With a wingspan approaching four inches it is the
largest of North American butterflies and the only one to take
part in a yearly migration that can total 3,000 miles. They do
this flying approximately 100 miles a day at sustained speeds
estimated at around 18 miles an hour, their wings beating five
to 10 times each second.
Scientists have observed precipitous declines in monarch
populations since the 1990s. The National Wildlife Federation
estimates the drop at an alarming 90 percent. Others put it
even higher. They attribute this to habitat loss and herbicide
use, both of which affect the availability of native milkweed
(genus Asclepias). Monarch larvae feed only on milkweed, and
they eat large quantities of it. The tiny caterpillar will increase
its size over 2,000 times before entering the pupa state.
Milkweed fuels this growth while its toxic properties provide
protection from predators. No milkweed, no monarchs.
We have known for many years that west coast monarchs
winter in Southern California, and there has been general
agreement that all monarchs east of the Rocky Mountains
winter in Mexico or South America. Recently scientists
noticed a sub-group in the Northeast that may not winter
in Mexico. The hypothesis is that they may, like many of us,
hunker down along the coast from South Carolina to Florida
or perhaps venture on to the Caribbean or possibly Cuba.
50
Photo by Sue Corcoran