We won’t know the acreage they cover until sometime in February, Garland said.

“They let the monarchs settle and then go in and do a careful survey,” Garland said of researchers in the Transvolcanic Mountain Range, about 62 miles north of Mexico City. “It takes quite a while.”

Chip Taylor, director of Monarch Watch, a nonprofit associated with the University of Kansas, predicted on his blog that the overwintering population will increase from 7.25 acres last year to 10 acres or better this winter.

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The Midwestern migrants have been hit hardest by population declines, said Kelly Mooij, New Jersey Audubon vice president of government relations.

“It’s mainly due to habitat loss and pesticides,” she said. Farms that used to have a lot of milkweed scattered among crops now eliminate it all through stronger pesticide use and use of seeds impregnated with pesticides.

Garland is leading a CMBO trip Feb. 23 to March 1 to three monarch butterfly reserves in the Transvolcanic Mountain Range. The trip is full and has a waiting list, he said.

“We are hoping it will be an annual event,” he said.