Peak Season at the Monarch's Winter Sanctuary in Mexico

Monarch Butterflies

Monarch Migration News: February 11, 2016
By Elizabeth Howard

It's peak season in Mexico now. As temperatures rise, the butterflies break out of their clusters and fill the air.

Art Howard, ArtWorks

News: A Critical Time is Passing

It's mid-February now and temperatures at the overwintering sites are starting to rise. Monarchs have survived the coldest part of the winter season.

"The really critical time for the monarchs is January and early February," says Dr. Lincoln Brower. "During that time, severe storms can be lethal when the butterflies are wetted by the storm and then subjected to freezing temperatures."

Conditions have been favorable this winter. Massive mortality from a severe winter storm has not occurred.

Peak Tourist Season
With rising temperatures the butterflies break out of their tight colonies during the day and fill the air. The next 6 weeks are the best time to see the spectacle.

People in the region depend heavily on ecotourism during the brief peak season as Estela Romero describes.

"The whole atmosphere in communities surrounding the Sanctuaries is of joy and smiles in people's faces. We all rush around, just as Monarchs do when the sun shines for them. This is indeed the best time of the year for most families in our region!" More...

Temperatures Rising

Ecotourism Peaks

Temperature and Survival

During the day it's usually warm at the monarch's winter home in Mexico, but at night it's as cold as the inside of your refrigerator. Sometimes it's even cold enough to snow. Why do the butterflies migrate across the continent to spend the winter in a place that is cold? Monarchs need cool temperatures to survive.

It's Cold in Mexico! During the day it's usually warm at the monarch's winter home in Mexico, but at night it's as cold as the inside of your refrigerator. Sometimes it's even cold enough to snow. Why do the butterflies migrate across the continent to spend the winter in a place that is cold? Monarchs need cool temperatures to survive.

“Since monarchs are cold-blooded, they do not use much energy when they are in a cool environment,” says Dr. Karen Oberhauser. Monarchs arrive in Mexico with fat (lipids) stored in their bodies. They eat very little, if anything, during the winter months. Because of the cool temperatures, they burn their food reserves slowly.

Cool Temperatures Help Monarchs Survive “Since monarchs are cold-blooded, they do not use much energy when they are in a cool environment,” says Dr. Karen Oberhauser. Monarchs arrive in Mexico with fat (lipids) stored in their bodies. They eat very little, if anything, during the winter months. Because of the cool temperatures, they burn their food reserves slowly.

Monarchs save energy by living in a cool place, but there are also dangers. If temperatures are too cold, they can freeze to death. Wet, cold monarchs are in particular danger. Ice crystals that form on the butterfly can kill it.

Cold Temperatures Can be Dangerous Monarchs save energy by living in a cool place, but there are also dangers. If temperatures are too cold, they can freeze to death. Wet, cold monarchs are in particular danger. Ice crystals that form on the butterfly can kill it.

Monarchs can't fly unless they can warm their muscles to 55°F. They can't even crawl below 41°F. The monarch pictured here can only crawl. It took one hour for this butterfly to crawl a few feet. Although monarchs can save energy when they are cold, the cold also makes them vulnerable.

Cold Temperatures Can Paralyze Monarchs Monarchs can't fly unless they can warm their muscles to 55°F. They can't even crawl below 41°F. The monarch pictured here can only crawl. It took one hour for this butterfly to crawl a few feet. Although monarchs can save energy when they are cold, the cold also makes them vulnerable.

"January and early February is the coldest time of the season. This is a really critical time for the monarchs," says Dr. Lincoln Brower. "We know temperatures below -8°C will kill about 50% of the monarchs. However, if the butterflies are also WET, it will kill close to 80-90% of the monarchs."

When Dangerously Cold? "January and early February is the coldest time of the season. This is a really critical time for the monarchs," says Dr. Lincoln Brower. "We know temperatures below -8°C will kill about 50% of the monarchs. However, if the butterflies are also WET, it will kill close to 80-90% of the monarchs."

If temperatures are too warm during the winter, the butterflies will burn their stored fat too quickly. Like running out of gas, they won't have enough to survive the winter and migrate north in the spring. Monarchs store lipids in their abdomen. With practice, a person can tell the condition of a monarch.

Warm Temperatures are Dangerous Too If temperatures are too warm during the winter, the butterflies will burn their stored fat too quickly. Like running out of gas, they won't have enough to survive the winter and migrate north in the spring. Monarchs store lipids in their abdomen. With practice, a person can tell the condition of a monarch.

Outside of the forest, temperatures can rise and fall sharply between day and night. Inside the forest, temperatures don't change as much. Dr. Lincoln Brower says the forest acts like a blanket and an umbrella. It protects the monarchs from cold and moisture. If the forest is cut or thinned monarchs will not have the protection they need.

The Forest Protects the Monarchs Outside of the forest, temperatures can rise and fall sharply between day and night. Inside the forest, temperatures don't change as much. Dr. Lincoln Brower says the forest acts like a blanket and an umbrella. It protects the monarchs from cold and moisture. If the forest is cut or thinned monarchs will not have the protection they need.

On a cool day you can see many ways cold temperatures affect monarch butterflies. For example, cold monarchs are clumsy when they try to fly. They often fall out of the air and land in funny places. This cold monarch landed on a mustache!

Visiting a Colony on a Cool Day On a cool day you can see many ways cold temperatures affect monarch butterflies. For example, cold monarchs are clumsy when they try to fly. They often fall out of the air and land in funny places. This cold monarch landed on a mustache!

On a cool day you often see monarchs on the ground. Strong winds and heavy rain can blow them down from their clusters. If the monarchs are cold, it may take hours — or even days — for them to return to the safety of the cluster. Slowly but surely, the monarchs pictured here are climbing back to the trees after being blown down by a storm.

Crawling to Safety After a Storm On a cool day you often see monarchs on the ground. Strong winds and heavy rain can blow them down from their clusters. If the monarchs are cold, it may take hours — or even days — for them to return to the safety of the cluster. Slowly but surely, the monarchs pictured here are climbing back to the trees after being blown down by a storm.

It even snows occasionally in the colonies in Mexico. "If buried by snow, monarchs might stay on the ground under the snow for more than a week!" says Dr. Bill Calvert. Amazingly, many can survive a snowstorm if they can stay dry.

Surviving a Snowstorm It even snows occasionally in the colonies in Mexico. "If buried by snow, monarchs might stay on the ground under the snow for more than a week!" says Dr. Bill Calvert. Amazingly, many can survive a snowstorm if they can stay dry.

On a cool day in a colony the forest floor is alive with shivering monarchs. The butterflies move their wings so quickly they’re blurry. You can hear the wings fluttering against nearby vegetation. Monarchs shiver to warm their muscles. After shivering, they can crawl and fly at temperatures that would otherwise be too cold.

Shivering to Warm Muscles On a cool day in a colony the forest floor is alive with shivering monarchs. The butterflies move their wings so quickly they’re blurry. You can hear the wings fluttering against nearby vegetation. Monarchs shiver to warm their muscles. After shivering, they can crawl and fly at temperatures that would otherwise be too cold.

On a cool day in a colony, you will always see butterflies climbing. They climb to the top of sticks, twigs, and tiny trees like the one pictured here. Monarchs struggle hard to get off the ground because the forest floor is dangerous. On the ground, they are exposed to predators, dew, colder temperatures and even frost and snow.

Avoiding the Forest Floor On a cool day in a colony, you will always see butterflies climbing. They climb to the top of sticks, twigs, and tiny trees like the one pictured here. Monarchs struggle hard to get off the ground because the forest floor is dangerous. On the ground, they are exposed to predators, dew, colder temperatures and even frost and snow.

Monarchs need cool temperatures to survive, but cool temperatures also present dangers. Shivering, crawling, climbing and flying to safety are adaptive behaviors. The forest microclimate provides the critical temperature balance the monarchs need to survive.

A Delicate Balance Monarchs need cool temperatures to survive, but cool temperatures also present dangers. Shivering, crawling, climbing and flying to safety are adaptive behaviors. The forest microclimate provides the critical temperature balance the monarchs need to survive.

What temperatures do overwintering monarchs need to survive? Explore the risk and benefits of the cold winter temperatures in Mexico's monarch sanctuaries.

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Next Update February 18, 2016