In this Dec 19, 2016 photo, a monarch butterfly is pictured at the oyamel firs (Abies religiosa) forest, in Ocampo municipality, Michoacan State in Mexico. (ENRIQUE CASTRO / AFP)

EL ROSARIO, Mexico - The population of monarch butterflies that arrived in Mexico’s forests to hibernate this winter fell 26 percent from a year earlier, the country’s Commission for National Protected Areas and the World Wildlife Fund (WWF) said on Thursday.

Millions of orange and black monarch butterflies migrate to Mexico on a 3,220-km journey each year from Canada across North America.

But the butterflies occupied only 2.1 hectares in December 2020, compared with 2.8 hectares the previous winter season, the conservationist group WWF said in a statement.

ALSO READ: Monarch butterfly numbers off for 2nd year in Mexico

People visit the Rosario Sanctuary - the winter home of Monarch butterflies - in the Ocampo municipality, Michoacan state, Mexico, on Feb 3, 2020. (ENRIQUE CASTRO / AFP)

Climate change had a “considerable impact” on the butterflies’ migration pattern, as well as the reduction in their milkweed breeding habitant in the United States, the WWF said.

Mexico’s western state of Michoacan is home to the country’s largest monarch butterfly reserve, typically a major tourist attraction. Visitors to the reserve have plummeted during the pandemic, sanctuary officials said.

In this Dec 19, 2016 photo, monarch butterflies are pictured at the oyamel firs (Abies religiosa) forest, in Ocampo municipality, Michoacan State in Mexico. (ENRIQUE CASTRO / AFP)