Michoacán, Mexico - Every winter, millions of monarch butterflies from the eastern part of North America migrate south to a forest in the middle of Mexico, where they drip from pine trees and coat mountain sides from November to late March.

The forest, which was first discovered in the 1970s, is officially called the Monarch Butterfly Biosphere Reserve, and has been a protected site in Mexico since 1980. But ever since then - and likely before - the forest has remained threatened by illegal logging.

On Tuesday, Mexican authorities took steps towards fighting that threat, in the form of the closure of seven sawmills that had been operating illegally in the reserve, according to the Associated Press.

The closures come around two months ahead of the butterflies' arrival and amid a wider crackdown on illegal logging in the area.

The total preserve is some 215 square miles, or about the size of Chicago. But a smaller, core area of the zone is where officials have focused their efforts, almost cutting in half the amount of illegal logging there from 2015 to 2016, according to the AP.

All of which is good news for the monarchs, who need all the help they can get. Although the number of Monarch butterflies that reached wintering grounds in Mexico rebounded 69% last year, their populations have been on the decline since 1996, when the Monarchs covered more than 44.5 acres (18 hectares) in the mountains west of Mexico City.

In addition to deforestation in Mexico's Butterfly Reserve, the monarch's existence is threatened by pesticides, commercial farming, global warming and other environmental issues, and scientists still aren't quite sure how - or if - they can be saved.