LOURDES GARCIA-NAVARRO, HOST:

And now an environmental story with good news. After years of decline, monarch butterflies appear to be on the rebound. These butterflies migrate some 2,500 miles from Canada to forests in Mexico every year. It's an arduous journey, and they've been hit hard by the use of herbicides and habitat loss along the way. But this year, the World Wildlife Fund reports that the monarch butterflies that are wintering in Mexico are covering a much greater area than last year. Jorge Rickards is field programs director with WWF Mexico, and he joins us via Skype from Mexico City.

Hello.

JORGE RICKARDS: Hello.

GARCIA-NAVARRO: So this is the second year that the numbers are up. What kind of numbers are we talking about?

RICKARDS: We are reporting four hectares of overwintering colonies. That's 9.1 acres. That is the area that they occupy, so that is indeed very good news compared to last year where we only had a little bit over one hectare.

GARCIA-NAVARRO: You've been out in the field with them. Just describe for our listeners what - if they haven't been able to see them, what these monarch butterflies look like when they come to stay in Mexico.

RICKARDS: Once they arrive to Michoacan - which is the name of the state where the forests are and the state of Mexico - they congregate on fir trees.

GARCIA-NAVARRO: High up in the mountains - I mean, it's quite a steep climb to get there.

RICKARDS: That's right. That's over 3,000 meters above sea level, so it is quite high. And they congregate all together and some cover the entire trunk of the fir trees. So it's so incredible to see that - all the butterflies aligned, one next to the other - and we're talking millions of butterflies. And the others hang on the branches to the point in which they actually bend the branches down. And what - they look like groups of grapes. You know how they look. How...

GARCIA-NAVARRO: Yeah. Yes.

RICKARDS: And during - in cold days, they are all dark and - because they're all concentrated - but as the temperature increases as the sun rises, they begin to fly. And that's the most wonderful spectacle because you're surrounded entirely by millions of butterflies.

GARCIA-NAVARRO: And they look like tiny little stained glass windows - orange and black stained glass windows. It's a spectacular sight. Why do you think these numbers are up? What responsible for this surge in the numbers of monarch butterflies?

RICKARDS: Climate is a factor. So climatic conditions might have helped. The higher presence of milkweed along the migratory route on the way back is also a factor that might have helped.

GARCIA-NAVARRO: And that's something, obviously, that the Obama administration set up a program to plant milkweed and to protect the butterflies from herbicide exposure along that migratory route. That was something that was put in place.

RICKARDS: That is right. It's still early to know the exact or direct effect of that. We would still need several years to confirm that trend. And that was also done through citizen science. And researchers in the U.S. have been working with people in monitoring the butterflies and also promoting the plant milkweed.

GARCIA-NAVARRO: Now we're seeing the monarch butterfly rebounding, possibly because of some of the actions that have been taken. What does this tell us about what we can do to save other species at risk?

RICKARDS: It is an example of how we can work together, from the scientific side, to generate very good data and answer the hard questions. As (inaudible) asked - are the things we do really impacting positively? It is also an example of how governments have worked together. When President Obama, Prime Minister Harper and the President Pena Nieto got together a couple of years ago, they signed this agreement. They established a high-level committee that has been working for these years. And we really wish we could have more of those cases. It certainly is an example to follow.

GARCIA-NAVARRO: Just to remind our listeners, though, the numbers are still way down from where they were 20 years ago, so there's still a long way to go.

Jorge Rickards is field programs director from the World Wildlife Fund in Mexico. Thanks so much for speaking with us.

RICKARDS: It's a pleasure. Thank you very much. Transcript provided by NPR, Copyright NPR.