Meteorologists in the United States over the weekend were puzzled by an enormous cloud that formed and began moving south towards Mexico. As it morphed from shape to shape, the scientists figured out what was going: An enormous cloud of Monarch butterflies were migrating to their winter time home in Mexico.

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In a post on Facebook, the St. Louis arm of US National Weather Service explained in decidedly scientific terms how it came to the conclusion:

“Sometimes our radars pick up more than precipitation. Check out this cool post from our Saint Louis Office!!
Keen observers of our radar data probably noticed some fairly high returns moving south over southern Illinois and central Missouri. High differential reflectivity values as well as low correlation coefficient values indicate these are most likely biological targets. High differential reflectivity indicates these are oblate targets, and low correlation coefficient means the targets are changing shape. We think these targets are Monarch butterflies. A Monarch in flight would look oblate to the radar, and flapping wings would account for the changing shape! NWS St. Louis wishes good luck and a safe journey to these amazing little creatures on their long journey south!”

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The monarch butterfly has also received less enjoyable attention lately for its extremely low population, coming close to extinction due to loss of habitat.

Via CityLab