Monarch butterflies wintering in Mexico could nearly quadruple in number this year thanks to actions taken by the United States, Mexico and Canada to protect the migratory species, authorities said on Thursday.

After years of sharp decline, the three countries agreed at a summit in February 2014 to form a working group to foster the insect's survival.

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More than a year later, the measures "are having an effect," Mexican Environment Minister Rafael Pacchiano said at a news conference at the Piedra Herrada monarch reserve alongside US Interior Secretary Sally Jewell.

Pacchiano said authorities hope the orange and black butterfly will occupy between three and four hectares (7.4 and 9.9 acres) of the mountain forest, located in central Mexico, this season.

"This is almost four times (the population) that arrived in the previous season," Pacchiano said, before a tour of the mountaintop, where hundreds of butterflies were resting or flying around fir trees.

The insect occupied 1.13 hectares of forest in the past season, better than in 2013-2014, when the population hit an all-time low of 0.67 hectares.

The goal is to reach six hectares by 2020. This compares to a high of nearly 19 hectares in 1996-1997.

Officials measure the size of the population by the area they cover instead of by individual numbers.

The falling population has been blamed on illegal logging in their Mexican wintering grounds and the drop in milkweed on which they feed due to the use of pesticides in the United States.

Pacchiano said Mexican authorities have launched "important" operations to combat illegal logging while Jewell said the United States is working on replanting milkweed in three million hectares of land and designating pesticide-free areas.

TagsInsects, Animal welfare, Conservation, Monarch butterfly, Mexico, Rafael Pacchiano, Monarch Butterfly Mexico