The Wintering Season Comes to an End
Field Notes from Mexico from Dr. Bill Calvert

March 17, 2005

Dr. Bill Calvert

It’s wet and rainy, peculiar weather for Mexico at this time of year.

Basking Butterflies Fly
On Monday, another group of us, nature lovers and teachers from many states climbed the 781 feet to the Rosario colony to find an ideal mixture of sun and clouds. The sun pulses between the clouds caused profound activity. Butterflies flew everywhere. The return of the clouds briefly increased their tempo as the basking butterflies pushed off into the air to avoid being trapped in exposed positions. (Read about the "cloud effect" for more information about this butterfly behavior.)

The night of Monday/Tuesday it began to rain. The skies opened, and it poured like the beginning of the wet season, maybe as much as two months early. It has been raining and occasionally hailing ever since. We dared not ascent the slippery slopes to the Pelon colony as originally planned. We reasoned that even the sure footed horses, a necessity at Pelon, would have trouble negotiating the steep slopes.

Every Year the Departure is a Little Different
We had heard that a period of intense hot weather last week and over the weekend, had driven the butterflies down slope, or down canyon, at Pelon and Rosario, and especially at Chincua. We also heard that the Herrada colony was no more: Dispersed and headed northward. Every year it’s a little different. Nature provides us with some interesting natural experiments to test our ideas about how things are. I hope we are paying attention.

Are the Monarchs Coming North?
Well yes, they have to be coming north. They are still many millions here, though, and they haven’t moved since Monday I’m sure. But last week they said there were three days of very, very hot weather (I’m not sure which days). And that’s when they left in great numbers and went north.

What Does it Look Like When the Monarchs Leave?
It depends on where you are, really. Where we are, around Angangueo, all you see is they’re descending the little arroyos and so forth, toward Angangueo, from Rosario. They’re just pouring down and into the town and then they keep going over the town and off to the north. (We haven’t seen that this year, but that’s what it looks like in prior years.) Another place that you see them migrating is when they’re leaving Pelon they cross the main highway and they’re headed from south to north. And if you take the trouble to go north of the colonies, north of Chincua, you can see many, many, many in the sky headed north. But from where we are, which is somewhat south of everything, we see very little at this time.