While the actual number of the colorful insects varies widely from year to year, it fell by nearly 30 percent over the past winter, according to experts.
They blame the decline on deforestation in Mexico, ongoing drought in Texas and the loss of the milkweed plants the butterflies feed on.
Monarchs go through four generations as they migrate each spring from Mexico’s Michoacan state to Canada and the northeastern United States.
That voyage can be daunting even when weather conditions are favorable and there is ample food.
“Milkweed is the key plant because it's the only plant where the female will lay her eggs,” said Chip Taylor, director of Monarch Watch at the University of Kansas.
He said there needs to be a national effort to save the butterflies, including the creation of “feeding corridors” of milkweed plants, planted in the right-of-ways along major north-south interstate highways.
Photo: Monarch Watch