Journey North Monarch Butterfly Spring 2003

Field Notes from Mexico
by Dr. Bill Calvert

March 17, 2003

It remains unseasonably cold in the mountains, and the butterflies still linger in their overwintering haunts. Cool sunny weather and lots of activity: A blizzard with butterfly snow being driven horizontally, or even upward. A ticker-tape parade where the particles are multicolored orange, black, and white. The shadows of the butterflies move continuously across the ground before you.

The colonies don’t look any smaller, and it’s hard to notice that the butterflies are leaving. But during the next two weeks, all that are here presently, tens of millions, will be leaving. They’ll be totally gone in two weeks.

Evidence now that some butterflies have started the northward trek are the tens of thousands of butterflies mobbing the senecios and eupatoriums (say, “u pa tor ee ums”) along the roads from Angangueo to El Rosario. At night these butterflies do not return to the colony, but rather form transient roosts on trees and in the arroyos at evening sunlight. Most of the butterflies mobbing the flowers are males. Why do you suppose males are taking nectar this time of the year? (Answer: They need more energy than the females, in order to carry the females during mating, and also to form the spermatophores.)

At El Rosario, the butterflies are still in the same position as last week, just below the Llano de Conejo and the Arroyo San Antonio and, ironically, over the hill from the elaborate cement stairway built for tourists to access them. Another small group is much lower in the same arroyo, but upward (about a 15 minute walk from the point where the forest ends and the field begins).

At Chincua the situation is much as it was the two previous weeks: Lose bough and trunk clusters are located in the Baranca Honda at a place known as “Tepusan,” named for the giant tepusan tree located nearby. This group is one kilometer from the canyon mouth. We do not know if another group is formed near the canyon mouth, poised to exit when conditions are correct, but based on past experience it seems likely.

Jim Edson and I will drive from here to Austin, Texas. Along the route north of the colonies we expect to see many, many monarchs passing by. We intend to leave on Sunday, March 23. We are going to cross-cross the area that we think the monarchs are going to be migrating through. Depending on the winds, they’ll be flying either low down, high up, or perhaps both. We’ll look at milkweeds for egg loads, eggs and larvae, and we’re going to be looking for flying adults.

We’ll travel from Michoacan to Hidalgo, then Querétaro, San Luis Potosi, Tamaulipas, and Nuevo Leon. We’ll go through cities like Tequisquiapan, Jalpan, Rio Verde, Ciudad Valles, Cuidad Mante, Cuidad Victoria and then we’ll probably go up to Monterry and then over to Loredo. It’s 900 miles to Austin, and we’ll probably put on about 1,200-1,500 miles.

The last part of the trip will be along the eastern face of the Sierra Madre Oriental, and we may dart west into the mountains if we have the opportunity and the time, to see what’s going on. Most of the terrain will be inner montane valleys and edge of mountains. On the coastal plain it will be warm, with daytime temperatures in the 70’s and 80’s. We’ll try to call in from the road next week, and tell you what we see.