"The really critical time for the monarchs is January and early February," says Dr. Lincoln Brower. "The lethal combination for the butterflies is to be wetted by a winter storm and then subjected to freezing temperatures."

Conditions have been favorable this winter. No severe winter storms have been reported.

"Monarchs have an excellent chance of getting through the winter in good numbers," says Dr. Chip Taylor.

Delicate Balance
Even though freezing is a risk during the winter, cool temperatures are essential for survival.

“Since monarchs are cold-blooded, they do not use much energy when they are in a cool environment,” says Dr. Karen Oberhauser.

Monarchs come to Mexico with fat stored in their bodies. They eat very little, if anything, during the winter months. Because of the cool temperatures, the monarchs can burn their food reserves slowly.

Microclimate is Key
A healthy forest habitat creates a microclimate that moderates temperature fluctations of surrounding climate. Outside of the forest, the temperatures rise and fall sharply between day and night. Inside the forest, the butterflies are protected from extremes.