Monarch butterflies recover from killer freeze
Date: 14-Mar-03
Country: MEXICO
Author: Karina Balderas
Tens of millions of black and orange Monarchs neared the end of their winter sojourn in the mountains of central Mexico this week to the relief of biologists who feared their numbers would be seriously depleted this year.
"We were waiting anxiously because we didn't know whether the butterfly phenomenon would be repeated after such a big kill," said biologist Marco Antonio Bernal, director of the Monarch Butterfly Biosphere Reserve in Michoacan state.
"We were astonished to see that, with good conditions in the United States and Canada, they could recover their population density and come to Mexico," he said.
Believed to be guided by the sun or the earth's magnetic field, Monarch communities fly several thousand miles from Canada and the northern United States to Mexico every year, arriving in October and November.
Monarchs spend winter in the pine-clad mountains of Michoacan state and the state of Mexico and fly to Canada in the spring.
Butterflies die during migration but also mate, making it possible for their descendants to complete the journey.
The migration fascinates scientists, who did not realize where the insects went every year until the mid-1970s.
"It is the only insect capable of making such a long journey, that's why it is called the Monarch," said Mexican biologist Alejandra Hinojosa.
Officials said some 83 million butterflies returned to Mexico this season to occupy 8.3 hectares of a 56,000-hectare reserve, 155 miles (250 km) from Mexico City.
Last year, reserve officials put the population at 93 million occupying 9.3 hectares, of which an estimated 65 million died when temperatures fell unexpectedly in January, 2002.
The cold snap led scientists to question whether the number of butterflies making the annual trek is actually much higher than previously thought. One scientific count estimated 270 million dead, or double the high end of previous estimates of the annual Mexico migration.
Floating like leaves amid the Oyamel fir trees, the butterflies engage in a final ritual before leaving Mexico: an airborne mating dance. By the end of March the forest will be virtually empty of them as they head north.
