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Deposing a Monarch from his Throne in the Sky
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By
Stephen Aitken |
05/05/2004 |
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The Monarch Butterfly is recognized by the black and orange markings that pattern its 8cm wingspan
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One
of the world's most spectacular biological events, the migration and the
over-wintering behavior of the Monarch Butterfly, Danaus plexippus, is
under serious threat. The black and orange markings that pattern the Monarch's 8
cm wingspan are recognized the world over and no other butterfly is known to
migrate distances up to 3,000 miles and over-winter in clusters with millions of
individuals. The conservation of the Monarch migratory phenomenon has become a
tri-national issue between Canada, Mexico and the USA. Though endemic to North
and Central America, the Monarch has recently expanded its range to include most
of Europe and Asia, thus its status has become an issue of international
importance.
The
Migration Phenomenon
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Monarch butterflies migrate distances up to 3000 miles over five subsequent generations
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There
are two distinct migratory populations of Monarchs, one west of the Rocky
Mountains and the other to the east. The former population over-winters in the
Eucalyptus groves of coastal California, while the latter migration is much more
spectacular in terms of density and length, spanning three nations.
Individual
butterflies migrate up to 50 miles per day and the entire migration to their
ancestral wintering grounds can be as far as 3,000 miles. Several
characteristics make this migration a highly unique phenomenon. One is that the
round trip is completed by as many as five generations before they return to
eastern Canada. Another is the intense clustering that takes place in the
over-wintering sites in the Oyamel Fir forests west of Mexico City. A living
carpet of insects sweeps over the trees, rocks and bushes and often tree
branches break under the collective weight of these 0.5-gram insects. There is
no host plant in this area of Mexico and the Monarchs leave their roosts only to
sip water from icy streams nearby. When the sun warms the resting butterflies,
they start to flutter, rising to a crescendo and ending in a deafening roar. In
the month of March, they start on their migration north, which is accomplished
in steps by up to five subsequent generations. A Canadian entomologist, Fred
Urquhart, discovered the spectacular over-wintering sites in 1976 and brought
them to the attention of the world through an article in National Geographic
Magazine1.
The
Habitats
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Tree branches often break under the collective weight of these 0.5-gram insects
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North
America - The Monarch
habitat all along the migratory path through the US and Canada is dependent upon
resident populations of milkweed (Asclepias) upon which the caterpillars
feed. In eastern Canada, the primary larval host is Common Milkweed (A.
syriaca), which accounts for 95% of the milkweed found there, while in
western Canada it is Showy Milkweed (A. speciosa).
Wildflowers
provide a nectar source for the adult butterflies, particularly during the fall
migration. At this time, sugars from the nectar are converted to the fat that is
essential for the Monarch to complete its migration and over-winter
successfully. Nectar sources also include Goldenrods (Solidago), Asters (Aster)
and Purple Loosestrife (Lythrum salicaria).
Recently
abandoned farmland in eastern Canada has created suitable areas for Monarch
breeding, since the host plant thrives in this type of habitat. As a result,
there has been a shift in the overall range of Monarchs into eastern Canada.
However, over the next several decades this habitat will decline as the farmland
gives way to the growth of trees and shrubs. The migration is vulnerable to the
loss of milkweed and nectar sources through landscaping, the growth of
succession forests as well as larval and adult butterfly mortality due to the
use of agricultural pesticides.
Mexico
- Forested ridge-tops west of Mexico City,
populated by Oyamel Fir trees (Abies religiosa), become the refuge for
over 100 million Monarchs, escaping the cold winter weather of Canada and the
northern USA.
Life
Cycle
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The caterpillar initially feeds upon its lost shell and later upon its milkweed host
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The
Monarch has four life stages: egg, larva (caterpillar), pupa (chrysalis) and
adult (butterfly). After a 5 to 10 day incubation period (depending upon the
temperature), the egg hatches into a caterpillar that initially feeds upon its
lost shell and later upon its milkweed (Asclepias) host. When the pupa is
formed, it hangs under a leaf for several weeks with the developing butterfly
inside. Finally, with the legs positioned downwards, the butterfly splits the
chrysalis and pumps fluid into its wings to harden them. The Monarch Butterfly
is ready for the world.
In
its summer territory, the Monarch mates three to seven times and the adult lives
2 to 6 weeks. When the days start to shorten, the hatching of non-reproductive
butterflies (in breeding diapause) is triggered, and these become the migratory
individuals that travel south to the over-wintering sites (though not all
Monarchs are migratory as Florida has resident populations).
The
Threats
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Monarch chrysalis
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Physical
- The principal threat to
this unique migratory phenomenon is the vulnerability of the over-wintering
sites. This spectacular seasonal event has provided tourist income to local
communities. As many as 300,000 tourists flock every year to the town of
Angangueo, Mexico. However the off-season practices are often environmentally
damaging and threaten the phenomenon itself. The impoverished local communities
harvest trees for construction, fuel and trinkets thus impacting the very
resource that provides the tourist-related income. The forests are getting
thinner and less able to buffer the protected areas from inclement weather, the
results of which became obvious in January 2002 when freezing rain and cold
winds killed up to 270 million Monarchs, approximately 25% of the reserve's
population2. Dead butterflies lay 30 cm deep
on the forest floor like orange and black snowdrifts. The Monarch can survive
under snow for several days but if the temperature stays below 0 ° Celsius for
a prolonged period, the mortality can be severe.
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Monarchs blocking the sun in the skies of Angangueo, Mexico
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Cultural
- The communal land system, organized into ejidos
- plots of land run and inhabitated by the local people though still owned by
the government - grants the poor rural population of Mexico fairly free access
to any and all natural resources. While US laws such as the Endangered Species
Act (ESA) and the Environmental Protection Act (EPA) can be enforced in this
region, the limitation of property rights, particularly the prevention of
logging and harvesting of other natural resources, are usually handled by
economic incentives i.e. the community receives financial compensation from the
government. For an impoverished country like Mexico, these incentives are an
expensive commodity and are very limited in number.
Initiatives
The
Monarch enjoys little protection under national or international regulations
because of its broad distribution and large populations. However the World
Conservation Union (IUCN) lists the over-wintering spectacle as an
"endangered biological phenomenon". The Mexican government made two
presidential decrees in the years 1986 and 2000, protecting forests around the
over-wintering sites. These have proven to be insufficient and at times merely
symbolic. The rate of forest degradation has tripled since the first decree3.
Current protection measures are inadequate in the face of the larger physical
and cultural threats to the Monarch habitat.
The
Zoological Society of San Diego (ZSSD) has been involved in conservation efforts
(habitat preservation) since 1999, working with the Bosque Modelo Mariposa
Monarca (BMMM), a non-government organization (NGO) based in Zitacuaro,
Michoacan, Mexico. They have been working to create income-generating industries
to benefit all of the ejidos, not just those that harbor the Monarchs4.
Conservation
Solutions
The
progress toward protection of the Monarch forests has been slow compared with
the rate of its destruction. Satellite images suggest that forest loss in Mexico
is occurring at a rate of 2.78 million acres per year, second only to Brazil.
The recent freezing incidences, due to the elimination of buffer zones, indicate
that the over-wintering phenomenon will end prior to the loss of the forests on
which the butterflies depend. This would be an international tragedy and the
loss of a truly unique natural phenomenon. A coalition of NGOs is required to
seek protection of the Monarch forest. A "Phenomenon Recovery Team"
should be charged with the initiation of a plan that would have legal powers
similar to the US Endangered Species Act model.
Global
attention is needed to protect the Monarch migration phenomenon, applying
international pressure with international funding to designate the
over-wintering sites as UN Cultural Heritage Sites with special protected
status. Concomitant action must be taken to improve the quality of life for the
communities directly impacted by the management of these sites. Only through
such a series of initiatives by international agencies can we ensure the
survival of the reign of the Monarch. Through international involvement, the
amazing migration of this beautiful species can become a symbol of international
cooperation and harmony. We must work together as one body to save the treasured
gifts of our planet.
* Stephen Aitken
is the International Coordinator of Tropical
Conservancy and the Managing Editor of Biodiversity, Journal of Life on Earth.
Visit the Tropical Conservancy website at: http://www.tc-biodiversity.org.
Your emails will be forwarded to him by
contacting the editor at: ScienceTech@islam-online.net
1.
Urquhart, F. 1976. National Geographic Magazine Vol. 150 No. 2, p.161.
2.
Anderson, J. B. and L.P. Brower 1996. Ecological Entomology 21, 107-116
3.
Bojorquez-Tapia et al. 2002. Conservation Biology 16:2, 346-360.
4.
Toone, W. and T. Hanscom 2003. Conservation of Monarch Butterflies in Central
Mexico: Protection of a biological phenomenon, Biodiversity Journal 4:4,
14-20.
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