How many millions of monarch butterflies are in a monarch colony? Scientists can only estimate. They say a monarch colony contains between 10 and 50 million monarchs per hectare of forest. (One hectare is 2.47 acres, about the size of two and a half football fields.)

Every winter scientists visit the 12 monarch sanctuaries and measure
the total area of forest covered by monarchs. This winter, the monarch colonies cover a total of 1.19 hectares of forest. How many millions of monarch butterflies are in Mexico this winter?

A monarch colony covers the trees in the El Rosario monarch sanctuary.

• A monarch colony is a large cluster of butterflies.
• A monarch sanctuary refers to the whole forest within which the colony moves.

• If there are 10 million monarchs per hectare there would be ____________ million monarch butterflies wintering in Mexico this year.

• If there are 50 million monarchs per hectare there would be ____________ million monarch butterflies wintering in Mexico this year.

• Based on these estimates, there are between _________________ and _________________ monarch butterflies wintering in Mexico this year.

Why Do Scientists Estimate?
Read the story about an event that caused scientists to raise their estimate from 10 to 50 million monarchs per hectare. Write and share your thoughts to these Reflection Questions:

• Why do scientists have to estimate the number of monarchs in Mexico?
• Why do scientists often say that they don't really know how many monarch butterflies are in a monarch colony?