Monarchs Continue to Arrive, Filling Out the Colony

The Cerro Pelón Chronicles: A Butterflies & Their People Project November 21–27

El Llano de Tres Gobernadores, Cerro Pelon Sanctuary, State of Mexico on November 25, 2017 at 10:51 am.

Migrating monarchs are still in the process of reaching their overwintering sites in Mexico. People in the villages surrounding the Cerro Pelón Sanctuary reported seeing them flying overhead throughout the week. Meanwhile on Cerro Pelón, CEPANAF Ranger Pato Moreno and the Butterflies & Their People arborists reported that their colonies grew visibly denser.

The week started off chilly. November 21 was cloudy and the arborists observed minimal flight activity. The next day was sunny but cool and the monarchs mostly stayed in their trees again. On November 23 it was sunny until noon, when clouds rolled in and all monarch flight activity ceased.

The blur of mating monarchs captured at 1:19 pm on November 24, 2017 in the Cerro Pelon Sanctuary. The wing of a dead monarch appears on the forest floor beneath them.

On November 24, temperatures had dropped enough that the arborists observed the first frost of the season, covering the meadow known as El Llano de Tres Gobernadores. Despite initially cool temperatures, the arborists documented a pair of monarchs leaving their reproductive diapause behind to mate.

November 25 also started out as a chilly day, but when the sun came out, the arborists were treated to the most active day of the season yet, as monarchs filled the meadow in great numbers.

Click here for video of November 25th Butterfly Storm in El Llano

The monarchs offset this physical exertion by nectaring. Many monarchs availed themselves of the salvia mexicana that’s currently in bloom at this elevation (3000–3,400 m) at this time of year. Lupine has started to emerge, but no monarchs were sighted feeding on its still immature blossoms.

Monarchs nectaring on salvia mexicana. Cerro Pelon, November 25, 2017 at 11:51 am.

Levels of monarch activity closely correlate to the temperature. If their body temperature is less than 13°C (55°F), they cannot fly. On November 25, temperatures inside their main roost were 10°C (50°F) at 10:30 am and 13.6°C (56.48°F) at noon, when their flying frenzy peaked in the meadow below, where undoubtedly temperatures were warmer. Temperatures fell to 12.5°C (54.5°F) by 2 pm and hit 9° C (48°F) at 5 pm. By late afternoon, all the monarchs were once again tucked away in the trees above.

As of Friday, the trees in the main monarch colony above El Llano started to appear more densely covered with monarchs. The smaller colony that had formed above this main grouping started thinning out, as more butterflies were drawn to the main colony below. However, the handful of trees in the colony on the other side of the mountain, in an area called Carditos, also started to appear fuller.

Main colony on Cerro Pelon at 1:53 pm on November 26, 2017.

According to conventional wisdom, the “peak” for monarch viewing falls in late February and early March. The sanctuaries are flooded with visitors during these few weeks.

What people don’t realize is that the warmer temperatures brought on by climate change are upending any and all conventions when it comes to monarch behavior.

The trickle of visitors who made their way to the sanctuaries in November have been greeted by impressive displays of monarch activity: they have seen flying, nectaring, puddling and even mating, in addition to the majestic sight of the clusters themselves. While these tourists are uniformly delighted by the sight of millions of frolicking monarchs, we’re left wondering about the long-term effects this increased activity will have on the viability of the migration.

Observations and images for this series were provided by the The Butterflies & Their People arborists, a forest protection and monitoring project made possible by our partnership with the Monarch Butterfly Fund.

Stay tuned for more updates on the monarch butterflies and monarch conservation efforts in Mexico. Here’s what’s been going on so far:

Week One: They’re Here!

Week Two: Colony Formation

Week Three: Colony Formation Continues

Week Four: A Spectacular Start

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