Monarch Butterfly Migration Update: February 23, 2000
Today's Report Includes:
Field Notes from the Mexican Monarch Sanctuaries
Students Visit the Sierra Chincua With Dr. Calvert
"It's hard to imagine how many butterflies this truly is! To put the number into perspective, convert butterflies to people. Imagine giving one butterfly to every person in your state or province--and then in neighboring states/provinces--until all the butterflies are gone.
Shivering Butterflies Litter the Ground
"You'll often hear people say the butterflies are trying to get warm enough to fly, but it may be that shivering helps them to crawl off the ground when they are too cold to fly. (Monarchs can crawl at temperatures as low as 5 degrees C. The monarch's flight threshold is about 13 degrees C, and in order to fly WELL, with lots of control, they need to attain thoracic temperatures pretty close to the temperatures that warm blooded mammals run - the upper 20s or even 30s. They can manage to get themselves airborne and glide--and occasionally flap with some control--at temperatures much lower than that, but they cannot fly well at temperatures in the teens.)
"Keep in mind that the temperature can sometimes drop to zero or even a few degrees below zero in the sanctuaries. Monarchs are paralyzed by temperatures this cold! When we were at the sanctuary this week it was during the peak warmth of the day. However, we did see some monarchs shivering that were down on the ground drinking water.
Why Do Monarchs Shiver?
My impression from observations is that the sunflecks (small circumscribed areas where solar radiation is entering gaps in the canopy and striking the ground) move around the forest each day and probably cover virtually all locations. So if it is sunny the day after a butterfly is grounded, a sunfleck will find its position sometime during the next day, and warm the butterfly enough to move out of its predicament. If there is a period of cloudy weather it's a different story, and the risk period could be much longer. If buried by snow, monarchs might stay on the ground under the snow for more than a week. But they are not at much risk buried under the snow, except perhaps by being stepped on."
Dr. Bill Calvert
Reporting from Angangeuo, Michoacan, Mexico
Eligio Garcia's Monitoring Data From Sierra Chincua
Once again, Eligio reports that the butterfly colony is continuing to move. This week, the main aggregation
is at 3,140 m altitude and only occupies 85 trees.
How Much Land Do Butterflies Need?
The area occupied by a colony at any moment is very small. As you know, this winter only 350 trees were filled with butterflies in the Sierra Chincua at any one time. However, work by Eligio and other biologists shows how important it is to monitor the monarchs over time. From Eligio's thesis: "If we consider all the land the colony occupies--from the time the butterflies arrive in November until their departure in March--it has been estimated that a colony will utilize 60 hectares." Bill Calvert says above that there are 400 trees per hectare, so the 350 trees at Chincu are roughly 1 hectare. This means the colony uses 60 times more land during the season that it does at any one time during the season!
Life in Sanctuary Region
Making Tortillas With Maria Luisa
Maria Luisa is a grandmother who lives in Los Remedios ejido. This ejido owns some of the most important land in the Sierra Chincua sanctuary. We hope these first-person accounts will portray the personal side of monarch conservation, as seen through the eyes of the children and families who live in the region. Watch for a new story each week, in both English and Spanish.
How to Respond to Today's Monarch Challenge Questions|
IMPORTANT: Please answer ONLY ONE
1. Address an e-mail message to: email@example.com