Monarch Butterfly Migration News

Monarch Butterflies

Conserving Energy
February 23, 2017 by Elizabeth Howard

Monarchs can survive all winter with little or no food. How? The cool forest is the secret.

Monarchs burn less energy when temperatures are cool.
Image Estela Romero, Journey North

News from Mexico
After this week's trips to the sanctuaries, Estela Romero reported that mating is still nowhere to be seen but should begin any day. Tourists are visiting from around the world and are delighted by the butterflies' performance and splendor. She remains concerned about this winter's unusually warm temperatures.

"Temperatures have been TOO HIGH for this time of year. Everyone around in town is commenting since we know it is not normal. Even in January some bright sunny days were reaching up to 22°C. How can the monarchs stand it? Let's hope it is more bearable for them in the forests."

Abnormally warm temperatures can present a problem: If it's too warm during the winter, the butterflies can burn their stored fat too quickly.

Lipids Falling
The graph shows how lipid levels change during the five months the monarchs are in Mexico. Their fat reserves should be about half gone by now. Have this winter's warm temperatures caused the butterflies to burn lipids more quickly? Running out of fat is a concern. Monarchs need enough fuel to survive the winter and to migrate north in the spring.

The secret behind the monarch's survival without food is the cool habitat it chooses in Mexico. "Cool temperatures in the forest slow down the monarchs' metabolism so they can stay alive longer," says Dr. Karen Oberhauser.

Monarch butterfly at sanctuary in Mexico.

Letter from Estela

Monarch butterflies survive winter in Mexico in the cool forest sanctuary.

Lipids Falling

Monarch butterfly at sanctuary in Mexico in snow.

Cool Forest Habitat

Surviving the Winter on Stored Energy

When butterflies arrive in Mexico, some are fat and others are thin. Look at each butterfly's abdomen, where its fat is stored. Which butterfly do you think is more likely to survive the winter? Running out of fat is a concern. Monarchs must survive on the food they ate before they went to Mexico.

Fat is Fit When butterflies arrive in Mexico, some are fat and others are thin. Look at each butterfly's abdomen, where its fat is stored. Which do you think is more likely to survive the winter? Running out of fat is a concern. Monarchs must survive on the food they ate before they went to Mexico.

When a monarch caterpillar eats milkweed, some food energy is stored as fat. A monarch caterpillar that finds plenty of milkweed becomes a big, healthy butterfly with a reserve of fat. This fat reserve will help a monarch survive the winter.

Voracious Eating as a Caterpillar When a monarch caterpillar eats milkweed, some food energy is stored as fat. A monarch caterpillar that finds plenty of milkweed becomes a big, healthy butterfly with a reserve of fat. This fat reserve will help a monarch survive the winter.

Adult monarch butterflies drink nectar from flowers. Extra food energy is stored as fat in the monarch's abdomen. Monarchs eat hungrily in the fall before—and during—their migration.

Voracious Eating as an Adult Adult monarch butterflies drink nectar from flowers. Extra food energy is stored as fat in the monarch's abdomen. Monarchs eat hungrily in the fall before—and during—their migration.

The secret behind the monarch's survival without food is the cool habitat it chooses in Mexico. "Cool temperatures in the forest slow down the monarchs' metabolism so they can stay alive longer," says Dr. Karen Oberhauser.

How do Cool Temperatures Help? The secret behind the monarch's survival without food is the cool habitat it chooses in Mexico. "Cool temperatures in the forest slow down the monarchs' metabolism so they can stay alive longer," says Dr. Karen Oberhauser.

This graph shows how much fat (lipid mass) the typical monarch has in each month of the year. Look how fat reserves change during the five months the monarchs are in Mexico.

Fat Reserves Month-by-Month This graph shows how much fat (lipid mass) the typical monarch has in each month of the year. Look how fat reserves change during the five months the monarchs are in Mexico.

There can be 50 million monarchs sharing a single hectare. Imagine how many flowers the monarchs would need. "There are some flowers near the colonies, but nowhere near enough for all of the butterflies," says Dr. Oberhauser. This is why stored fat is essential to survival.

So Many Butterflies, So Few Flowers There can be 50 million monarchs sharing a single hectare. Imagine how many flowers the monarchs would need. "There are some flowers near the colonies, but nowhere near enough for all of the butterflies," says Dr. Oberhauser. This is why stored fat is essential to survival.

Monarchs do need water to survive the winter. On warm days, the butterflies fly out of the colonies by the millions to drink. At first, scientists didn't realize water was so important. Now they know that protecting the watershed of the forest is an important conservation need.

What About Water? Monarchs do need water to survive the winter. On warm days, the butterflies fly out of the colonies by the millions to drink. At first, scientists didn't realize water was so important. Now they know that protecting the watershed of the forest is an important conservation need.

In order to survive the winter, monarchs must obtain energy from milkweed and flowers before they reach Mexico. Next they need the cool temperatures of the Mexican forest to conserve energy. Monarchs need high quality habitat in both places for winter survival.

The Habitat Connection In order to survive the winter, monarchs must obtain energy from milkweed and flowers before they reach Mexico. Next they need the cool temperatures of the Mexican forest to conserve energy. Monarchs need high quality habitat in both places for winter survival.

Companion Resources

Driving Question

Monarchs can survive five months of winter in Mexico with little or no food. How does the forest habitat make this possible?

Report Your Sightings


Report all monarchs you see — adults, eggs, larvae.

What to Report	Winter Adults report \| map \| list	Winter Eggs report \| map \| list

Winter Larvae report \| map \| list	Milkweed report \| map \| list	Other Observations report \| map \| list

Next March 2, 2017