I. Introduction:
Monarch butterflies by the hundreds were in the field before me. It was a sight that was simply beautiful and breathtaking. Why were they all here though? Did they come here to die together? The purpose was a mystery to me. The answer was even more magical than I could have imagined. They were heading home to ..:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />Central Mexico where they spend the winters. This was a mass migration in progress. Wikipedia lists the Monarch butterfly's scientific name as Danaus plexippus, which in Greek literally means "sleepy transformation" (Wikipedia 2007). According to the article "Monarch Butterflies" on the World Wildlife Organization web site, the name, which evokes the species' ability to hibernate and metamorphism, actually inspired by a Greek myth called Danaus. His daughters flee Libya for Greece in order to avoid marrying their cousins (WWO 2007). The long, migratory journey of the Monarch butterflies is reminiscent of their flight. Where were they going? Why were they going? There are many theories about the journey taken by monarchs but there is no complete answer as mysteries remain. Their future is also in question.
II. The Cycle of Life:
"A flight of butterflies" by Jonathan Weiner talks about how the Monarch butterflies have a complete life cycle that takes them through a complete metamorphosis. This metamorphosis involves four different cycles or stages which are egg stage, larva/caterpillar stage, pupa, and adult stage. The adult monarch lives only a short time ranging from four to five weeks (Weiner 57). The U.S. Dept. of Agriculture's Forest Service web site makes clear the monarchs that leave in the fall are not the same monarchs that left Mexico last spring or even the ones that were around in the middle of the summer. This migrating generation which is sometimes called the "Methuselah generation" is headed back to Mexico is some 3 or more generations removed from the ones that began the journey from the overwintering site in the spring (USDA.FS 2007). Taking a moment or two to let this sink in, one truly begins to understand the amazing journey back to Mexico. The monarchs that leave in the fall have never been where they are going and there is no leader to show them the way. This is a journey that may be as far as 3,000 miles according to the U.S. Dept. of Agriculture's Forest Service web site (USDA.FS 2007).
In "Migration of the Masses" Dalrymple and Gottfried discuss how the monarch butterfly adapts to survive. Nature or evolution has helped them make there journey by adapting their life cycle. The last generation born is different than the others over the summer. This last generation is in a reproductive dormancy that will aid the journey south. It will help the monarch conserve energy that is needed for the flight. Not only are they in a different sexual state but their life span has increased greatly as well. The migrating butterflies live seven or eight months. They make the journey and then "hibernate" at the overwintering site. Then when spring returns they finish their sexual growth, mating takes place, and new generations begin the flight northward with adults again only living four to five weeks (Dalrymple and Gottfried 1995).
The northward monarchs in the spring lay eggs that become grow to adults and the progression northward continues its progress until fall comes again (USDA.FS 2007). Normally three or four more generations will have evolved again before the migrating southward starts again. This also helps to build the population for the long journey that awaits this insect in the fall. It is the only insect that migrates this far and losses of population need to be replenished each year.
III. Masses on the move
As many as 300 million monarchs will make their way to the overwintering in Central Mexico in the Transvolcanic Plateau. The migration starts in August and continues through November and even December (Rankin 46). There are an unknown number of losses along the way from dangers in such a long journey. Storms, predators such as birds, and even humans (vehicles are not butterfly friendly) take their toll on the migrating monarchs (Hanson, To, Nguyen 1). If that is not enough they face more danger in Mexico where weather can play a larger role in killing thousands more monarchs through strong storms, temperature, and even snow may be present as they complete their journey. Those that make the journey are tired and ready to hibernate in the fickle conditions of the Transvolcanic Plateau.
They feed heavily on the nectars of flowers to sustain their daily journeys. "There does not appear to be a social grouping in the migration and monarchs may fly alone for up to six hours a day. They do not fly at night as they stop to rest in suitable trees (Dalrymple and Gottfried 36)." They have been measured at some 12 miles per hour and average 50-100 miles per day but the longest recorded one day total is an amazing 265 miles(USDA.FS 2007). The migration can take up to two months to complete (USDA.FS 2007).
The monarchs are believed to use a combination of things to get them where they need to go such as the Earth's magnetic field, the sun, and physical land forms (Hardman 3). They are able to orientate their direction by the location of the sun throughout the day and throughout their journey.
Researchers have even found small pieces of magnetite inside of the monarch's body. This naturally occurring magnet used to be called lodestone and was used in early compasses (Hardman 3). It is believed this small piece of iron that is affected by the Earth's magnetic field is a big piece in the migration of the monarchs (Etheredge 85). They are able to follow the magnetic field. This does not answer all of the questions though on how they travel.
Once the monarchs reach the mountains of Mexico they turn left and follow the mountains. This is crucial as the mountains lead to adequate supplies of food and water before eventually leading to their overwintering sites (Hardman 3). If they did not turn precisely towards their over wintering site as they enter Mexico they would fly directly into the Pacific Ocean, away from the shelter and food to survive the winter. The Sun helps guide them as does the Earth's magnetic field but how do they know to turn at that precise spot? It is believed they switch their navigational tools and now follow land forms such as the mountains (Hardman 3).
It is this unique combination that makes the migration possible for the monarch to reach the sites where it can survive the winter and keep the species going for generations to come.
V. Home and Their Future:
The long journey south ends at the wintering sites located in Mexico's high altitude fir forests of the Transvolcanic Range. "In this 20-by-40-mile strip of mountains, hundreds of millions of monarch butterflies find refuge in a dozen patches of forest at elevations of around 10,000 feet (Rankin 46)." This range is unique and yet the possibility exists that it could be gone as Mexico tries to balance the needs of the monarch with the needs of the farmers who desire the Oyamel fir trees. Only two of eleven known roosting sites are well protected today (USDA.FS 2007).
The battle to protect their home in the Oyamel forest is complicated as it puts human needs versus the monarch's needs. It is a battle the monarch's are not capable of fighting and yet is one they can not lose. The battle truly comes down to money and the farmers need for additional income (Brower et al. 346). In "Quantitative Changes in Forest Quality in a Principal Overwintering Area of the Monarch Butterfly in Mexico, 1971-1999" discusses how the Oyamel trees are valuable and harvesting them provides needed income. The current battle is trying to convince the farmers that there is another way to make money and leave the monarch habitat in place. The idea is to convert some of the farming areas into tourist locations. If the farmers can be convinced to see money by protecting the monarchs then the battle to protect the monarchs becomes easier. Currently, despite regulations and laws to protect the monarchs the forest is slowly disappearing (Brower et al. 346). Money wins the battle even if slowly.
As Hanson, To, and Nguyen make clear in their piece, "The migratory behavior of the monarch butterfly", the problems facing the monarchs are not limited to Mexico and their overwintering sites (Hanson, To, Nguyen 1). In Canada, on the other end of their northern range, has declared milkweed a noxious weed and it is illegal to grow it. If it is found in either public or government land it is destroyed. Monarchs only feed and lay their eggs on the milkweed. The Canadian Government has recently begun to make some butterfly reserves where milkweed is allowed (USDA.FS 2007).
In the United States milkweed is considered a nuisance and often is destroyed. Farmers kill it with pesticides and land that used to be left to wild flowers is often now replaced with grasses to look more appealing. The monarchs are facing a tough battle (USDA.FS 2007).
A reason for the battle is the fact that monarchs and their unique nature has only recently come to light. "Lepidopterists have been watching throngs of fluttering monarchs since at least the 1850's, but not until 1930 were scientists able to conclude with certainty that monarchs migrate south for winter and north in early spring (Rankin 46)." "Much of what biologists know is brand new (Rankin 46)." It was only in 1976 that Lincoln Brower even found the monarchs winter sites (Rankin 46).
He and his colleagues climbed to 9,000 feet, where they entered chill, foggy Oyamel fir forest. "We walked in along this trail that went down along a ridge for a mile, and we didn't know exactly where the butterflies were," Brower recalls. Then, abruptly, the deep greens of the firs were lost in a dazzling cataract of orange, and Brower realized he was looking at a wall of butterflies. "I couldn't believe the density and numbers," he says. "The next day it warmed up, and when the sun came up, the butterflies were flying all over the place. It was like walking into the Charles Cathedral and seeing light coming through the stained glass-windows. This was the eight wonder of the World." (Rankin 46)
VI. Conclusion:
Hanson, To, and Nguyen quote Feltwell from his book "The Natural History of Butterflies. Facts on File. Inc." published in 1986 that, "No other animal is more typical of a healthy environment, nor more susceptible to change, than a butterfly" (Hanson, To, Nguyen 1). These beautiful butterflies that make a miraculous journey are vulnerable to nature but their biggest threat is human nature. We must decide before they are gone if we can truly afford to lose them forever. Despite our ever changing World of concrete and technology they have survived and that is admirable. However, they cannot survive the loss of habitat and money should not be allowed to be the reason.
Works Cited
1. Brower, Lincoln. "Quantitative Changes in Forest Quality in a Principal Overwintering Are of the Monarch Butterfly in Mexico, 1971-1999".
_Conservation Biology_ 16.2 (2002) 346-59. _Academic Search Primer_.
EBSCOhost. SMCC Library, S.Portland, ME. 11 October 2007
< http://web.ebscohost.com/ehost/detail?vid=7&hid=15&sid=4d6135db-c69a-4aab-ad2c-ab82e62ed816%40sessionmgr3>.
2. Dalrymple, Marcus. "Migration of the masses".
_Geographical_ 16.3 (1995) 36-39. _Academic Search Primer_.
EBSCOhost. SMCC Library , S.Portland, ME.
11 October 2007 .
3. Hardman, Chris Mackey. "Magnetic Migration".
_Americas_ 50.6 (1998) 3. _Academic Search Primer_.
EBSCOhost. SMCC Library. S.Portland,ME. 11 October 2007
< http://web.ebscohost.com/ehost/detail?vid=10&hid=15&sid=4d6135db-c69a-4aab-ad2c-ab82e62ed816%40sessionmgr3>.
4. Rankin, Bill. "On the track of the monarch butterfly".
_National Wildlife_ 35.3 (1997) 46-52. _Academic Search Primer_.
EBSCOhost. SMCC Library. S.Portland, ME.
11 October 2007.
5. Etheredge, Jason. "Magnetic Personalities".
_Economist_ 353.8147 (1999) 85. _Academic Search Primer_.
EBSCOhost. SMCC Library. S.Portland, ME. 11 October 2007.
6. "Monarch Butterflies." _World Wildlife Organization_. 15 October 2007.
7. "Monarch Butterfly." _Wikipedia._ 27 November 2007. Wikimedia Foundation. 28 November 2007.< http://en.wikipedia.org/wiki/Monarch_butterfly>.
8. Hanson, Karen, Nicki Nguyen, and Hein To. "The Migratory behavior of the Monarch Butterfly." _Butterfly Website_ 30 October 2007
9. United States Department of Agriculture:Forest Service. "Monarch Butterfly North America's Migrating Insect." 27 August 2007. _Washington: U.S. Dept. of Agriculture:Forest Service_. 29 November 2007.
< http://www.fs.fed.us/monarchbutterfly/>.
10. ..> --> D(["mb","..u003cdiv style..u003d.."direction:ltr.."..>..u003cspan class..u003dsg..>..u003cbr /..>..u003cbr /..>--..u003cbr /..>New Online Store!!! Visit it today. Lloyd..'s Journey prints, calendars,..u003cbr /..>tiles, cards, and more!!!..u003cbr /..>..u003cbr /..>..u003ca onclick..u003d.."return top.js.OpenExtLink(window,event,this).." href..u003d.."http://www.cafepress.com/lloydsjourney.." target..u003d_blank..>http://www.cafepress.com..u003cwbr /..>/lloydsjourney..u003c/a..>..u003cbr /..>..u003c/span..>..u003c/div..>",0] ); D(["ce"]); //--> ..> Weiner, Jonathan. "A FLIGHT OF BUTTERFLIES." _Sciences_ 23.3 (May 1983): 57. _Academic Search Premier_. EBSCO. SMCC Library, South Portland, ME. 30 November 2007. .
0 comments:
Post a Comment