Monarch Butterflies Dwindle Due to Harsh Winter Weather

Researchers see precipitous drop in annual migrating popuation.

ByABC News via logo
March 21, 2010, 9:14 AM

March 21, 2010— -- Monarch butterflies normally find sanctuary in the mountains of Mexico, away from the cold winters of North America, but a harsh winter of torrential rain and mudslides has decimated the monarch butterfly population.

"We saw a number of things happen in Mexico this winter that shouldn't be happening but are probably due to climate change in some way," said Chip Taylor, director of Monarch Watch at the University of Kansas.

This year's intense storms may have killed more than half of the butterfly population. Not even sticking close together under tall fir trees as they normally do could protect them from the downpours and freezing temperatures.

"One of the things that's predicted from climate change is you see a lot of moisture coming into central Mexico in the dry season and that moisture came in with a passion this winter, and it was just very destructive," Taylor said. "We had 15 inches of rain over a three-day period, and it was just devastating.

"It was pretty clear that in some locations 80 percent of the butterflies had been lost, in other locations it had been 20 to 30 percent, and in other places it was 50 percent or more loss," he said.

According to Taylor, it's the lowest number of monarchs returning to the United States that he has ever seen.Monarch butterflies in the eastern U.S. follow a remarkable migration pattern as winter nears, traveling thousands of miles down to Mexico using a sort of instinctual GPS system. When the weather warms in March, breeding monarchs head back north to repopulate. By summer the butterflies migrate as far north as Canada.

Around this time each year, sightings of the tell-tale orange-and-black wings are reported from Florida to Texas, but this year there has been about a quarter of the usual sightings in the south.

While researchers suspect climate change and the destruction of their habitat in the U.S. and Mexico as the cause of the population's precipitous drop, it may also be a natural phenomenon.