Monarch Migration Update: February 16, 1999
Today's Report Includes:
Mexican Monarchs on National Public Radio Next Monday
Tune in next Monday morning, February 22, for a National Geographic "Radio Expedition" to the monarch sanctuaries in Mexico. The program will include an interview with monarch biologist Dr. Lincoln Brower during a recent trip to the Sierra Chincua and Rosario overwintering sites. It is scheduled to be broadcast on NPR's Morning Edition (7-9 am), and after airing will be archived on the WWW at:
Field Notes from Mexico by Dr. Bill Calvert
A strong, cold air mass from the north (called a "norther" ) has blown deep into Mexico, bringing unseasonably cool temperatures. It's downright COLD for this part of the world!
We haven't been to the sanctuaries since cold weather hit on Thursday, so we have yet to see the effect of this storm system. But past experiences indicate that cold weather--accompanied by snow, sleet, hail and high winds--is bad news for butterflies.
Last week, when warm and dry, butterflies at the El Roario and
Sierra Chincua sanctuaries were extremely active, traveling as much as 1 km out from the colonies to drink water
and take nectar. Butterflies numbering in the thousands, and in some cases tens of thousands, were a common sight
at seeps and wet spots where streams cross roads.
How Many Monarchs are in Mexico?
Last week, we asked you to imagine counting all the butterflies in Mexico. Meet Eligio Garcia Serrano who's job it is! Eligio works for the Mexican government's National Institute of Ecology (Intituto Nacional de Ecologia, "INE") and is graciously forwarding news to Journey North this spring. Now how do you suppose these scientists go about estimating the monarch population size?
In last week's update, Bill Calvert gave a clue about WHEN it's best to count butterflies: He said the monarchs cluster tightly together during the coldest months. This is exactly when biologists make their estimates. They travel to all the monarch sites and measure the total surface area that all the clusters of butterflies cover.
Here's another clue from Dr. Calvert: "In 1986, we did a 'mark & recapture' study at one of the sites in January. On the basis of that study we estimated 13,000,000 monarch per hectare. Albeit crude, you can use that figure to estimate the size of the total monarch population for a year."
According to Eligio's measurements, in total this year the monarchs cover less than 6 hectares. Significantly, almost 4/5 of the population is found in only 2 sanctuaries. Here are his measurements for the winter of 1998/1999:
Since monitoring began, the lowest coverage recorded was 3.5 hectares. Here are the records from the past several years. (Get ready: You'll need a little Spanish to do today's Challenge Question!)
How Many Monarchs on a Branch?
1. Address an e-mail message to: firstname.lastname@example.org
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