Monarch Butterfly Field Notes from Mexico by Dr. Bill Calvert

Field Notes from Mexico by Dr. Bill Calvert

March 3, 2004

Photo: Jim Edson

Dr. Calvert Calling Journey North from Mexico

(Audio File mp3)

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This week we are a group of teachers and ex-teachers, some with spouses, from Georgia, North Carolina and New Jersey.

We visited the butterfly colonies at Rosario and Chincua. We were told that the original size of the Rosario colony was 4.5 hectares, measured by Marco Antonio Bernal (Sanctuary Director) and his crew from SEMARNAP. The current size is about 20 trees, not very completely filled. If the forest density here is 400 trees per hectare, and we assume the same density of occupancy, what is the percent decline at El Rosario?

Chincua still occupies about 1/2 hectare. The outlier groups of small clusters apparent last week in the descent to the colony have disappeared. Presumably they joined the main colony below. The main colony has moved slightly downstream since last week. It appears healthy and robust. Many butterflies saunter out from the colony and drift through the forest, gracing it with their color and brilliance.

Among the spouses this week are two foresters. It was most interesting to see the forest through the eyes of foresters. They found the forest of the Sierra Chincua to be mostly healthy. There are enough gaps to promote regeneration of seedlings. The forest floor was almost devoid of fuel wood, but some was present to provide decaying, organic matter for the soil. Only in a few places were there small stands of dead trees that could provide a fuel ladder to the canopy and provoke a crown fire.

Below the ridge of Chincua there was evidence of a ground fire within the past 5 years. Understory was sparse, and there were hardly any birds. Up on the ridge, the understory was more dense providing seeds and habitat for insects, both supporting a more abundant bird fauna.

The recovery of nectar plants is evident. Both species of Senecio are in bloom, Eupatorium is mobbed with nectaring monarchs, and mass mating has begun. It is spring in Mexico.

Maps and images of monarchs at their winter refuge in Mexico.

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