The graph shows:

• Lipids are the highest in November. This is the month when monarchs arrive at the overwintering sites in Mexico.
• Lipids fall in November, December, January, February and March. These are the months that the monarchs spend in Mexico.

Running out of fat is a common cause of death in Mexico, says Dr. Bill Calvert. "Monarchs that you see littering the ground have usually starved to death."

When the monarchs arrive in Mexico in November they must have enough fat in reserve to survive the winter. Their winter habitat does not have enough food (flowers with nectar) to feed the millions of monarchs that overwinter there.

However, the monarch's winter habitat does meet the monarchs needs in a unique way. Its cool temperatures allow the monarchs to save energy. Monarch butterflies are cold blooded. When temperatures are cool they burn energy (metabolize) slowly.

Journaling Questions

• If your weight were to fall at the same rates as the monarchs do between November and April, how much would you weigh today?
• A monarch tag weighs 10 mg. How many times that weight does the average monarch lose by the end of the overwintering season?
• If it is true that monarchs do not eat while they are in Mexico, then when and where DID they get the food energy that they are burning now?