How Many Millions of Monarchs? Every winter, scientists visit Mexico's 12 traditional sanctuaries and measure the area of forest covered by monarchs. Scientists measure area because estimates of individual butterflies in a colony vary too widely to be reliable. Such estimates range from 10 to 50 million monarchs per hectare. In winter 2018/2019, the colonies covered an area of 6.05 hectares (as of December, 2018). Using data from this winter, you can see how imprecise estimates of individual butterflies are. A colony in El Rosario sanctuary. A monarch colony is a large cluster of butterflies. A monarch sanctuary refers to the whole forest within which the colony moves. Try This! Monarch Math Estimate the number of butterflies in 6.05 hectares of forest. If there are 10 million monarchs per hectare there would be ____________ million monarch butterflies wintering in Mexico.   If there are 50 million monarchs per hectare there would be ____________ million monarch butterflies wintering in Mexico. Based on these estimates, there are between _________________ and _________________ monarch butterflies wintering in Mexico.