Illegal loggers have chopped their way deep into unique forest reserves in a mountain range in central Mexico where millions of monarch butterflies from eastern North America roost for the winter, according to researchers who posted satellite photographs of the area on a NASA Web site Wednesday evening.

Forests of oyamel fir trees in Michoacán and Mexico States have for thousands of years been a winter haven for the resplendent orange and black butterflies, the most famous “charismatic megafauna” of the insect world, said Lincoln P. Brower, a professor emeritus of biology at Sweet Briar College in Virginia, who has studied the butterflies and their shrinking winter habitat for decades.

The images, posted online at earthobservatory.nasa.gov, show fresh clear-cutting in an area that held large butterfly colonies last year, as seen in aerial surveys, said Daniel Slayback, a geographer based at the NASA Goddard Space Flight Center in Greenbelt, Md., who has been tracking the butterfly wintering grounds with Dr. Brower. The images were taken by the commercial Ikonos satellite for the Monarch Butterfly Sanctuary Foundation, a group with which