Picture a fir tree 50 feet tall and covered with a million motionless butterflies, one on top of the other, resembling clumps of dead leaves hanging from dozens of sagging branches. For 30,000 years, scientists say, tens of millions of monarch butterflies have flown south for the winter in a migration that resembles that of birds. It's one of nature's unique and spectacular performances.
Some monarchs travel as far as 4,000 miles round trip, all the way from eastern Canada to an isolated ridge in Mexico's Transvolcanic mountain range.
After 30 years of searching for it, American scientists found the monarch's winter destination in 1976 - with the help of a local shepherd.
Only monarchs from east of the Rockies (about 100 million of them) go for the extended Mexican holiday, staying from November until mid-March. About 10 million Western monarchs prefer to hang out at about 50 sites along California's coast.
Last winter, 50,000 visitors came to the remote Mexican ridge here outside Angangueo to see the butterfly-clad trees. On sunny days there's an extra bonus. The sun warms the insects until they take flight, filling the sky with fluttering orange wings.
Since 1985, six of the Mexican site's more than 30 butterfly colonies have been protected in a preserve called El Refugio de la Mariposa Monarca (Refuge of the Monarch Butterfly).
It isn't easy to get to see the butterflies at rest. The Monarch Refuge is near the town of Angangueo, one of the oldest gold- and silver-mining towns on the continent, and a four-hour drive northwest from Mexico City.
Allow another hour for the steep, unpaved, and very eroded road from Angangueo to the refuge. Arranging a ride on a local, open-air cattle truck is the best way to attempt it. A regular car might not get through.
You can also get a ride at any Angangueo hotel. Price is negotiable, generally under $5 per person.
Two of the preserve's roosts are open to the public - for an entrance fee of less than $1 - while the others are reserved for research. A new visitors center with a small museum was completed in 1986. Nearby, a one-mile trail leads you on a short but steep walk to the monarchs' doorstep.
Although the monarch site is at a tropical latitude, it's also at 10,000 feet. Both rain and snow are possible, and so are sunny, 70-degree temperatures. Dressing in layers and taking a hat is recommended.
Bring both low ASA film (ASA 64 or 100) for sunny days and higher-speed film (ASA 400) in case it's overcast.
Zoom or telephoto lens (80 mm and above) will enable you to get close-ups of butterfly clusters on the trees, and a flash will help overcome shadows of the forest.
In August 1986, 50,000 forested acres, including 12,000 acres of monarch preserve and the rest a buffer zone, became the country's first official wildlife sanctuary.
The government's action came in response to warnings from scientists and conservation groups, such as the World Wildlife Fund and Mexico's Monarca AC. They held that uncontrolled tourism and logging operations threatened to destroy the area's precious habitat and the unique migration site.
While the problems aren't yet entirely solved, this measure has brought renewed hope.
By March, the warming spring temperatures gently recharge the well-rested monarchs. Each day more leave the ridge, following their internal compasses north.
Finally, by mid-month the fir trees are empty again, as the last of the butterflies ride their thermals back home.
If you go
Two hotels in the area are recommended. Hotel Albergue Don Bruno is new, and it has a beautifully landscaped inner courtyard in addition to 21 comfortable and clean rooms at about $15 a night. There's also a good restaurant with local specialties. (Address: Morelos No. 92, Angangueo, Michoac'an, Mexico.)
Hotel Spa San Jos'e Purua - in a quiet, scenic setting - is about a 2-hour drive south of the preserve. It's also less than 10 miles from Zit'acuaro, a town just south of Angangueo.
The hotel's facilities include tennis, horseback riding, disco, and thermal baths. Room rates (with meals) start at about $20. (Address: Reforma y Esq. Calle Colon 27, Mexico 1, D.F.)
Turistoria in Mexico City, offers Saturday-Sunday excursions to the monarch site during much of the winter. Write them at S.A. de C.V., Insurgentes Centro No. 114-209, Mexico D.F., Mexico; or call 592-8137 and 703-1544.
Similar trips are offered by Holbrook Travel Inc. of Gainesville, Fla., 3540 NW 13th St., Gainesville, FL 32609, (800) 451-7111, and Betchart Expeditions Inc., 10485 Phar Lap Dr., Cupertino, CA 95014, (408) 245-9517.