Mexican human rights activists are raising alarms after the disappearance of a well-known conservationist in western Michoacan state.

Homero Gómez González, who has spent years protecting the monarch butterflies who migrate to Mexico each winter, was last seen on Jan. 13, according to the state’s human rights commission.

Although the circumstances of his disappearance remain unclear, commission official Mayte Cardona told Reuters her organization has asked the attorney general’s office to investigate whether it is tied to his conservation work.

“He was probably hurting the [business] interests of people illegally logging in the area,” Cardona told the news agency.

Parts of the forest where the monarchs winter in Michoacan have been damaged by illegal loggers in recent years, displacing butterflies. But Gómez González and other conservationists have helped restore much of the natural environment. In 2018, World Wildlife Fund reported that forest degradation in the region had decreased dramatically, but warned illegal logging was on the rise.

Gómez González, a former commissioner of the town of Rosario, manages the local butterfly reserve. In an article published this month, he told The Washington Post that the protection of the species is steeped in local traditions. The people of Michoacan have long welcomed the remarkable annual migration of the insects who travel thousands of miles from the United States and Canada to Mexico to escape the winter weather.

“Our grandparents told us, ‘Take care of them. They’re angels,’” he said.

Gómez González’s Twitter feed is full of photos and footage of the insects. In some videos, he stands amid swarms of swirling butterflies as they land on his face and shoulders.

He tweeted several times the same day the human rights commission said he was last seen. One post shows a group of smiling tour guides, dressed in matching blue jackets, standing at the entrance to a butterfly sanctuary. Another shows groups of butterflies fluttering in the forest.

More than 61,000 people have disappeared in Mexico, authorities reported this month, a dramatic increase from earlier government estimates. More than 97 percent of the disappearances have been reported since 2006, when Mexican authorities ramped up their crackdown on drug traffickers and cartels.

Environmental activists are often targeted in Mexico and elsewhere in Latin America. In 2017, gunmen killed indigenous Mexican activist Isidro Baldenegro López, who had been honored with the prestigious Goldman Environmental Prize in 2005 for his work protecting forests from logging.

Baldenegro López was the second Goldman recipient to be killed in less than a year, following the 2016 killing of Berta Cáceres, a Honduran activist who protested against a controversial dam.

Amnesty International said in October it had recorded the killings of 12 activists defending Mexico’s land, territory and environment in the first nine months of 2019 alone.

They included Samir Flores Soberanes, who was shot to death in the state of Morelos last February. The motive behind his killing was unclear, but thousands of people protested his death in Mexico City, amid suspicions it was linked to his work protesting a controversial pipeline project. The state’s attorney general opened an investigation into his killing last June, Amnesty reported.