Colony Formation Continues on Cerro Pelón

The Cerro Pelón Chronicles: A Butterflies & Their People Project

November 8–12, 2017

Citizen scientist observations inform much of what we know about monarch butterflies’ annual 3,500-mile migration from Canada to Mexico. But during the monarchs’ five-month-long stay in Mexico, very little information their timing, location and behavior reaches the public. (I talk about some of the reasons why here.) This series is an effort to fill that gap and connect our on-the-ground citizen science and conservation efforts with monarch lovers everywhere.

In the Cerro Pelon Sanctuary, three forest rangers employed by the State of Mexico (CEPANAF) spend all day every day observing and protecting the monarch colony. Recently they were joined by three Butterflies & Their People arborists, a forest protection and monitoring project made possible by our partnership with the Monarch Butterfly Fund. The arborists took the photos for this piece, while CEPANAF Ranger Pato Moreno recorded these observations about the second week of butterfly season 2017–18. (Click here to read about week one.) -E.S.

Butterflies & Their People arborists Carmelo and Pancho in El Llano de 3 Gobernadores on Cerro Pelon, State of Mexico. This season’s colony is forming up on the mountain behind them. Photo by Pato Moreno.
It was another amazing week with the butterflies on Cerro Pelon. It was cold and clouds covered up the sun by 2 pm every day, sending the temperature plummeting. Cool weather meant that we didn’t see as many monarchs flying about. Some did however leave the colony to seek out the purple blossoms of salvia mexicana, which seems to be their preferred nectar source among the flowers in bloom at this time of year.


Butterflies & Their People arborists are monitoring the nectar sources near the monarch butterfly colony on Cerro Pelon. As climate change pushes average temperatures up, the monarchs have become more active across the season. Last season we witnessed flight activity almost every day: their state of semi-hibernation seems to be a thing of the past. They will need to eat more to compensate.

On Saturday the Butterflies & Their People arborists and I went hiking to another part of the mountain to see another colony we’d heard about. The butterflies were clustered in even more trees than in the colony that has formed above El Llano, but this area isn’t open to the public. I think it’s good that there are some colonies that are always left alone — that way we can make sure there are always butterflies around to make the trip back north.

Secret colony not open to the public on Cerro Pelon. On 11/11/17 monarchs covered an estimated 50 trees.

On our way back to El Llano, we passed by another roost of monarchs, but as soon as they sensed our presence they started flying out of their trees. We kept our distance, so as not to startle them any more than we already had.

Before monarchs form a more permanent roost, they are easily startled. Even though the monarchs start arriving in early November (Oct 27 this year), the butterfly sanctuaries in the State of Mexico and Michoacan aren’t open to the public until the third week of November, so that the monarchs have time to settle in.
It’s been really good to see so many monarchs arriving, and we suspect that there are many more still to come. The sense of peace that nature gives us, especially when its filled with beautiful butterflies, is something that few people get to experience. So even though it can be chilly and sometimes rainy when we’re making our rounds up on the mountain, we feel blessed in our work.

— CEPANAF Forest Ranger Pato Moreno (Translated by Ellen Sharp)

Read more about the progress of the Monarchs in Mexico:

Week One: They’re Here!

Week Two: Colony Formation

Week Four: A Spectacular Start

Cluster, Cerro Pelon, November 9, 2017.

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