How Cold Are the Overwintering Sites in Mexico?
On average, overnight low temperatures hover just above freezing while the monarchs are in Mexico. These temperatures are similar to those in your refrigerator! The forest shelters monarchs by keeping a very delicate balance: If temperatures were too cold, the butterflies would freeze to death; if temperatures were too warm, they would burn their stored fat too quickly.
With regard to temperature, "The really critical time for the monarchs is January and early February when it's the coldest time of the season," says Dr. Brower. "We know temperatures below -8 degrees C will kill about 50% of the monarchs. If the butterflies are WET, it will kill close to 80-90% of the monarchs."
Thinking More About the Graph
- To get
comfortable with the concept of "average low temperature,"
record your own low temperature each night for a few days, then calculate
the average.
- How many degrees did your temperatures fluctuate above and below the average?
- Dr. Brower says "-8 degrees C will kill about 50% of the monarchs." Look back at the graph. Draw your temperature fluctations beside the values shown. Did your average temperatures fluctate enough to be of concern?
- Write the temperature for each month on the graph in degrees Fahrenheit. Then edit the scale to Fahrenheit. (Here is a conversion scale to help you.)
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