MEXICO CITY — The number of Monarch butterflies wintering in Mexico has plunged this year to its lowest level since studies began in 1993, and experts say the insect's annual migration from the United States and Canada could disappear.

A report released Wednesday by the World Wildlife Fund, Mexico's Environment Department and the Natural Protected Areas Commission blames the dramatic decline on the butterflies' loss of habitat due to illegal logging in Mexico's mountaintop forests and the massive displacement of the milkweed plant it feeds on in the U.S.

The black-and-orange butterflies now cover an area of only 1.65 acres (0.67 hectares) in the pine and fir forests west of Mexico City, compared to 2.93 acres (1.19 hectares) last year. They covered more than 44.5 acres (18 hectares) in 1995.