NEW YORK - It's the first week of spring and monarch butterflies are leaving their winter home in Mexico - beginning a journey that will take them all the way to Canada. The first of the migrating monarchs have just been spotted in south Texas.
Last year, CBS News correspondent Seth Doane reported their population was down 75 percent, But now, they're making a comeback.
Last year, Hundreds of millions of monarch butterflies clustered for warmth in the trees of Mexico. But the butterfly population then was actually at an all-time recorded low - as over-development and illegal logging decimated the forests.
This year, the trees were dripping in butterflies while millions more were filling the skies above. Butterfly colonies cover nearly 10 acres of forest - that's double the area last year.
Conservationist Bill Toone of the EcoLife Foundation says that's good news, but "All that has to be kept in perspective with the fact that last year was the lowest number of butterflies in Mexico since we started recording in 1993."
Why the rebound? The Mexican government has made progress fighting illegal logging, down 97 percent in two years. But weather gets most of the credit. This winter there was no major freeze in central Mexico. A good spring last year in America produced a robust crop of milkweed, the solitary food source for monarch caterpillars.
Monarch experts, gathered last month in Kansas say these butterflies help pollinate of hundreds of plant species.
Lincoln Brower - whom we first met in Mexico - worries about modern farming techniques. "Part of the impact on monarchs now is industrialized agriculture - which is destroying the milkweed food plant habitat - the breeding habitat of the butterfly."
140 million acres of monarch habitat have been lost in the last 16 years in the U.S. That's an area 3 times the size of Illinois - another test of this tiny insect's resilience.
For more info: