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Flying With the Butterflies
by Carol Cullar

February 27, 2003

Here's an actual photo of the front edge of the Valle de Bravo flow, which
demonstrates
the use of the warmth of the highway and the lowness of the butterflies' flight, using
the lift created by
"ground effect."
Carol Cullar

Just returned from an 8 day trip to the preserves around Zitacuaro! Wanted to assure everyone that the monarchs are alive and well and headed our way in just a few more days!

We visited 4 preserves: El Rosario, Chincua, Capulin, and Valle de Bravo. For the last two days we were accompanied by Eligio Garcia Serrano and experienced on two occasions (at Capulin and Valle del Bravo) rivers of monarchs flowing down off the mountains using the highway itself as a conduit to facilitate their flight.

Eligio said that in his ten years collecting data and monitoring the monarchs, he had never before had the opportunity to observe such a movement!

The flow at Capulin was 90' wide, and we monitored the central flow in a rectangle 15' x 30' and had a continuous rate of 40-45 PER SECOND. We broke the 90' flow into 15' segments (except for the center segment of 30'): the flow dropped off in a bell curve and timed estimates from the edges were between 0-20 individuals. Between 15' and 30' and 60' and 75' the estimates were between 10 and 20 individuals. In those areas we took an average with 10 on both edges, 15 in the midsections, and 42 for the center average. This resulted in an extrapolation of 5,520 per minute, 331,200 per hour, and for 5 hours of the flow from 10 a. m. to 3 p.m. a populaton of 1,656,000 which were moving at 20 to 25 mph.

The stark numbers in no way enable me to describe what it was like to stand in the road and be surrounded with their orange fluttering filling the air, to feel the wind of their passage and, even in my hearing empaired state, to hear the passage of their wings!

We went back the very next day and observed no monarchs flowing down from Capulin. When we arrived at Valle de Bravo there was a similar, but much smaller population using the road under the aegis of heavily armed state police, who enforced a slow crawl of the traffic through their ranks. We rolled down our car windows and, sticking our arms out the window "flew along" with the migration!

Carol Cullar, Executive Director
Rio Bravo Nature Center Foundation, Inc.
Eagle Pass, TX


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