http://www.commondreams.org/headlines03/1111-06.htm
Published on Tuesday,
November 11, 2003 by the lndependent/UK
Climate Change Threatens Butterfly's 2,000-Mile
Migration
by Steve Connor
The unique life cycle of the monarch butterfly - which migrates
more than 2,000 miles to its wintering grounds - could come
to an end within 50 years, according to a study published
yesterday.
Each year, monarchs
migrate south to the high mountain forests
of Mexico from their summer breeding sites as far north as the
border between the United States and Canada. Scientists have
discovered that the oyamel fir trees of Mexico on which the
butterflies spend the winter are highly vulnerable to the
changes in climate that meteorologists have forecast for
the next 50 years.
By then, according
to computer predictions made by Karen
Oberhauser of the University of Minnesota and Townsend Peterson
of Kansas University, few of the oyamel forests will be able
to provide the vital protection that the monarchs need to survive
a cold winter. "In fact, when current oyamel distribution
was
included in models to be projected to future climates, none of
the present wintering sites was predicted to be suitable in
50 years' time," the researchers say in the journal Proceedings
of the National Academy of Sciences.
With its bright orange-and-black
markings, the monarch is
one of the most beautiful butterflies. It is also one of
the most intriguing because of its extraordinary migratory
route, which is believed to have evolved since the last Ice Age.
When winter comes to
an end, millions of the monarchs fly
north out of the Mexican mountains to feed and breed on the
spring and summer forest flowers virtually throughout the
entire North American continent. In September, four or five
generations later, the monarchs newly emerged from their
chrysalises as far north as the Great Lakes begin their
long journey to the Mexican mountains, sometimes finding
the same tree used by their great-great-grandparents the
previous winter.
Dr Oberhauser said
that the oyamel fir forests of central
Mexico provided a unique microclimate for the butterflies
that allowed them to spend up to five months in their wintering
grounds.
Although climate change
is not expected to affect significantly
the winter temperature of the oyamel forests, rain and snow
is predicted to increase. This would make it more difficult
for a butterfly that requires dry weather.
Dr Oberhauser added:
"The relationship between winter mortality
and weather conditions suggests climate-change may have important
impacts on monarch butterflies."
It is not just climate
change that could see off the monarch.
"Degradation of the forests in which monarchs overwinter
is a
real and serious threat to their survival." Logging and the
conversion of woodland into farmland, as well as forest fires,
are all putting pressure on the long-term survival of the
monarch. "Our analyses suggest that climate-change effects
may pose an additional long-term risk to monarchs,"
Dr Oberhauser said.
The scientists point
out that the monarch may be expected
to survival climate change better than some animals that
cannot migrate. However, their highly specific requirements
for surviving the winter months make them especially
vulnerable to any changes.
Monarchs also face
threats on their northern breeding grounds,
where milkweed, the plant that larvae feed on exclusively,
is considered a noxious weed and often destroyed.
A series of studies
published last year demonstrated that
monarchs were able to navigate vast distances using an
internal clock.
They use the clock
to calculate the correct direction
in which to travel, with the Sun serving as a compass.
© 2003 Independent
Digital (UK) Ltd
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