Field Notes from Angangueo, Mexico
Contributed by Dr. Bill Calvert
March 14, 2000
With reports we'd been hearing about butterflies arriving the earliest ever in the
southern United States--and speculation about the unusually warm winter driving the butterflies north prematurely--we
were all a little apprehensive about what we'd find in the sanctuaries.
When we passed by the Herrado colony on Sunday the 11th, we saw only a few hundred butterflies descending the mountain
where hundreds of thousands had been seen 3 weeks before. It didn't help either when I called a friend who lives
close and she said, "You've come to see the butterflies? They've all left, haven't they?"
Not withstanding all these negative reports and speculations, in 24 years of Mexican monarch watching, I'd never
seen the colonies break apart substantially before the 20th of March--and indeed had often seen butterflies in
substantial numbers here into early April.
And when we arrived at El Rosario, our worries were totally dispelled. We were greeted by tree, after tree, after
tree, fully laden with dark, clustered butterflies. When the sun appeared, they filled the sky above and between
The colony had descended from its high position near the Llano de los Conejos, down
the Arroyo Rio Grande almost to the forest edge. The butterflies were highly scattered among the trees, and there
were a few trunk clusters. This is the usual situation for this time of year, but not the uusal postion. Normally
they come down above the Ejido Rosario, but this year they had graced Ejido La Salud and presumably enriched their
Several of us had wandered to an area where the trees were heavily laden with butterflies
that were especially close to the ground. We were staring and photographing when a sharp snapping sound rang out.
A branch full of butterflies came down, spilling its colorful cargo all over the ground. They immediately began
to rise by opening and closing their wings. Those on the upper side of the branch began to fly off in uniform motion
and direction. Those on the bottom were trapped by the weight of the branch. Gingerly we lifted the branch and
allowed them to escape. The branch was not small--perhaps 6-7 feet in length, so many thousands had come down with
it. But within one half hour only a handful were left in the spot where the branch had fallen. So it seems falling
with a branch does not seem to harm many of them.
Mating was going on everywhere. Hundreds of attached butterflies peppered the ground beneath the trees occupied
by the butterflies. These numbers represented at least a ten fold increase over what we witnessed 3 weeks before.
As usual, the mated pairs seem to be the largest females and small males.
The receptionist at our hotel told us the monarchs had been descending into Angangueo every day between the 8-12
to March, but had not come down yet that day (March 13th). Walking through the colony later on the 13th, we were
able to speculate why. The ground was peppered with raindrop pockmarks. It seemed reasonable to suppose that a
small thunderstorm had occurred the day before and the weather had turned unseasonably moist and cool. Only a slight
cooling of the air temperature perhaps caused by increased cloudiness will prevent the butterflies from descending.
It seemed this had occurred at both Rosairo and Herrado on the 13th.
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