Monarch butterflies, hit hard by strong storms at their winter home in Mexico, have dwindled to their lowest population levels in decades as they begin to return to Texas on their springtime flight back to the United States and Canada.

The monarch loss is estimated at 50 to 60 percent and means that the breeding population flying northward is expected to be the smallest since the Mexican overwintering colonies were discovered in 1975, said Chip Taylor, a professor of entomology and director of Monarch Watch at the University of Kansas.

"I think it is very clear that the butterflies lost more than half of the population," Taylor said. "I'm hoping it wasn't as high as 70 or 80 percent. We've never seen it this bad before."

The butterfly colonies in the Mexican state of Michoacan were hit by torrential rainfall and mudslides in early February that also killed at least 40 people and left thousands homeless. Several towns were devastated by flooding.

Researchers put the butterfly population in Mexico at 1.92 hectares, down from the average of 7.44 hectares. The hectare count represents the areas with trees that contain monarchs. There is no consensus on how many monarchs can be in a hectare, but researchers say the number may be as high as 50 million.

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