The number of Monarch butterflies wintering in Mexico dropped 28
percent this year, according to a report released Thursday, a decline
some experts attribute to droughts in parts of the United States and
Canada where the butterflies breed and begin their long migration south.
Others say damage to wintering grounds in central Mexico's mountains
remains a factor in the decline, citing deforestation of the fir and
pine forests they favor.
The numbers of butterflies spending the winter in Mexico have varied wildly in recent years.
Concern rose two years ago, when their numbers dropped by 75 percent
in the wintering grounds, the lowest level since comparable
record-keeping began in 1993. They partially recovered last year, when
the number of butterflies nearly doubled from that record low point.
"Fluctuations in insect populations are normal. In the case of the
Monarch, we have shown that these fluctuations are mainly due to climate
conditions," said Omar Vidal, head of World Wildlife Fund in Mexico,
adding that "during 2011, the abnormal patterns of drought and rainfall
in breeding grounds in Canada and the United States ... could have
caused high mortality rates and a lack of plants" on which the
butterflies feed.
But others were more worried.
Lincoln P. Brower, an expert on monarch butterflies and zoology
professor at the University of Florida said this year's number is the
third lowest since systematic monitoring began, adding "the current data
indicate a continuation of the downward trend."
Brower said the climate argument "ignores the fact that severe
degradation of the Oyamel (fir) forest ecosystem has been and still is
occurring."
Vidal said a survey indicated that only about an acre (half-hectare)
of trees were lost to deforestation last year, down two-thirds from the
preceding year.
Illegal tree-cutting destroyed about 3.7 acres (1.5 hectares) in 2010,
itself a decrease of 97 percent from 2009. At its peak in 2005, logging
devastated as many as 1,140 acres (461 hectares) annually in the
reserve.
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