Friday, March 16, 2012
Monarch Butterflies Mexico Migration Dropped This Year by Mark Stevenson
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.