|
Dear Journey North,
By
1976, Lincoln Brower was very familiar with the monarch butterfly
whereas I knew virtually nothing about it at all. He had already
investigated the chemistry of the creature and had discovered
that protection was conferred upon monarch larvae and adults by
virtue of the larvae eating poisonous milkweeds and incorporated
some of the poison into their own tissues. Many, but not all,
predators that ate them became sick and learned to avoid monarchs
and all butterflies that looked like monarchs. This relationship
became the keystone of a new discipline launched by Brower and
others called ecological chemistry.
At that time I was working in Amherst, Massachusetts on a project
studying tent caterpillars. I knew of Brower's reputation, but
had not met him until after an afternoon seminar when we chanced
to talk of the monarch migration in my home state of Texas. I
hadn't been home in some time and was feeling a little homesick.
I volunteered to make a collection of migrant monarchs in Texas
for his studies. I learned a great deal about monarchs that week,
mainly that they were well ahead of me. I had to go into Mexico
to catch up with them and make the collection.
After
returning to Massachusetts, we began to talk about the article
published in the August National Geographic magazine by Fred Urquhart
about the newly discovered monarch overwintering sites in Mexico.
Brower had written Urquhart asking for the location of the Mexican
colonies so he could use them in his studies. Urquhart refused
to disclose the location of the colonies — even to the scientifically
renowned Brower — citing a need for secrecy to protect them.
We began immediately to dream and scheme about locating the overwintering
colonies ourselves. We found two facts mentioned by Urquhart in
his articles especially interesting. These were the altitude of
the colonies and their location in the state of Michoacan, Mexico.
The state of Michoacan is huge, but it you draw lines around the
3000-meter contour (~10,000 feet), you will find that only a few
massifs extend above this altitude. It was a simple matter to
find a good map showing these contours. It was a bit harder to
mount an expedition to the town of Angangueo smack in the middle
of the highlands of Eastern Michoacan.
With a handpicked group of friends and Mexico experts in a beat-up
borrowed truck, we drove down from Texas, presented our butterfly
sample pressed between plastic sheets to the mayor of Angangueo.
He was astonished that anyone would be interested in such a creature,
but willingly arranged for his nephew to guide us up the mountain
where the monarch wintered in the millions. After a day of hard
trekking at 10,000 feet elevation, we arrived at the colony about
dusk and, after catching our breath, gaped at the astonishing
spectacle of millions of monarchs gracing a mountain glade in
the mist of a tall cypress forest.
In spite of the speed in which we found what became known as the
Chincua colony, it was a wonder that we had found it at all. The
map published in the August National Geographic Magazine shows
the sites to the hundreds of miles north of where
they actually are. One of the articles mentions their location
in the Sierra Madre mountains, whereas the butterfly colonies
are located in the Transvolcanic Belt. National Geographic makes
excellent maps. We used one of theirs to locate the massifs described
by Urquhart. Yet the map in the article was way off. Could they
have been trying to confuse us? Maybe - we will probably never
know.
The first-discovered colony was located in a cypress forest. This
turned out to be uncommon. The cypress forests share a high altitude
habitat with firs (known locally as Oyamels), a few pines and
some oaks. The dominant species is Oyamel. Most of the high massifs
that we outlined on the National Geographic map had Oyamel forest.
The distribution of Oyamels in Mexico is extremely limited. They
are thought to be remnants of forests that were much more extensive
when the climate was colder and wetter. The forest retreated up
the mountainsides to retain the cool, moist climate to which the
trees are adapted. The Oyamel forests are confined to the high
massifs, and the high massifs are few and far between. It is likely
that the monarchs seek out these high mountain habitats for the
same reason the Oyamel forest ended up there--it's cool and relatively
moist up there at a time when the rest of that part of Mexico
is parching in the dry season.
Dr.
William Calvert
|
