Monarch Migration Update: March 9, 1999
Today's Report Includes:
How Will They Know When it's Time to Go?
Spring is now advancing rapidly across the monarch's breeding grounds in the north. As you read today's report, think about this:
Winter Monarch Sightings: Map and Data
Field Notes from Mexico by Dr. Calvert
The weather remains cool and dry in the Transvocanic belt of Mexico, with temperatures ranging from low 80's (F) during the days and high 40's (F) at night. Clouds usually build up around the mountains in the afternoons, keeping temperatures from climbing. Notwithstanding the coolness, sometime after Eligio's March 1 measurements, the butterflies at Sierra Chincua moved downslope. They now sit at least 300 meters lower than their position in late February, and are strung out along a side drainage that leads from the Mojonera Alta on the high ridge to the main channel of the Barranca Honda. The Chincua colony is quite narrow, maybe 20 meters wide, and has budded--that is, it is split in places into separate colonies. These bud colonies are separated by less than 50 meters, so they are still more or less together.
At the nearby el Rosario sanctuary, the movement downward is restricted. Because the forest has been cleared for farming, they cannot descend anymore. (Some conservationists are concerned that the important downslope staging areas are not adequately protected.)
The most spectacular behavior occurring during this time in March is "cascading". Literally tens of thousand of butterflies suddenly push off their perches, en masse, and fall downwards. After a fall of 3-5 meters they begin to fly, all in the same direction. The phenomena is absolutely awesome. Butterflies fill the sky at all levels for a period of up to several minutes. Gradually they fly out of the area or land in nearby foliage--with only green spots on the branches where the tens of thousands of butterflies had recently been. Sometimes one cascade will trigger another, resulting in a sequential cascading from numerous branches in the colony.
There are times during the over-wintering period that bird predators can also trigger a cascade in a butterfly colony. But the phenomena that we witness in March is orders of magnitude greater than any cascading associated with the presence of birds. The local people believe it is the noise made by people observing the butterflies that causes cascading. However, no one has shown that monarchs can "hear" airborne sound waves. Monarchs do seem to cascade in response to the presence of people, and this is of concern.
Field Notes from Eligio Garcia
Intituto Nacional de Ecologia
Here are Eligio Garcia's measurements of monarch "coverage" at the Sierra Chincua sanctuary:
"Realizamos un recorrido por Senguio, Campo Hermoso, Maravatio y Dolores y observamos que muchas mariposas ya estan regresando al norte. Tambien observamos que hay muchas mariposas volando en Cierra Chincua y posiblemente la proxima semana ya se halla ido toda de Sierra Chincua, " said Eligio. "I hope not!", added Bill Calvert. (He's leading a teacher tour to Sierra Chincua next week.)
Weather Report from Pedro Ascencio School
How Cold is the Monarch's Mexico?
Discussion of Challenge Question #5
According to data collected by the Pedro Ascencio students during the week of 15 February, wasked which day was the warmest and which night was the coldest? Fourth graders in Mrs. Allen's class in Pueblo, Colorado noted that the warmest day was Thursday at 72 degrees F, and the coldest nights were Monday and Wednesday at 37 degrees F.
Each morning the students are also noting whether there is dew ("rocio"), frost ("helado") or none ("nada") present. Why is this important? This region of Mexico is dry tropical forest. Because the monarchs are here during the dry season, sources of water can be scarce. The monarchs drink dew early in the season (Nov/Dec), but as temperatures drop (Jan/Feb), dew is no longer available and the butterflies must fly to open sources such as streams and seeps to drink. By noting whether dew or frost are present, we know if this important source of water is available to the monarchs that day.
Why More Males Than Females?
Discussion of Challenge Question # 9
Miss Bailey's student at Citrus Elementary School in Vero Beach, FL responded:
"Our class thought about why no female monarch butterfly wings were left near a watering hole by a predator, and wrote their guesses in their butterfly journals. Most thought it had something to do with the level of toxic chemicals (cardenolides) in the monarch's body. Amber Pastir thought, "The females protect themselves very well because they maybe eat a lot more milkweed than the males do. So the females might be more poisonous than the males." Evan Brown agreed, "They eat milkweed and get poison from it." (firstname.lastname@example.org)
Toxic cardenolides are an excellent defense mechanism for monarchs. And female monarchs have a 30% higher concentration of the toxins than do males, on average. (Females probably do not eat more milkweed, but their bodies retain more of the chemicals.)
As we saw last week, monarch predators have different methods of consuming their prey. According to research by Brower and Fink (1981) orioles vomit after eating only small amounts of the toxin, whereas grosbeaks can ingest larger amounts of the toxin without vomiting. The toxin is stored in the monarch's abdomen in the "cuticle". Looking back at the 2 bird's methods of feeding, notice that the grosbeaks consume the entire abdomen whereas the orioles "unzips" the abdomen and avoids eating the cuticle. Although they have more poison, there are advantages to eating females: Females contain 26% more lipids, so if a predator can tolerate the female's poisons it can benefit from her fat.
How Many is 56 million?
Discussion of Challenge Question #6
From Iowa-Grant High School in Livingston, WS (email@example.com) Nicole and Emily discovered they could give 1 butterfly to each person in each of these states!
How to Respond to Today's Monarch Challenge Questions
1. Address an e-mail message to: firstname.lastname@example.org
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