Snowstorm in Mexico


(This column was first published in the February 25, 2002 Buffalo News.)


We expect snow in Buffalo. Aside from the late December and early February storms, however, we have had very little this season. That certainly does not, of course, mean that we are out of the woods. Lake Erie remains open and March and April snow events are not unusual.


But snowstorms in Mexico?


Indeed, the Mexican Transvolcanic Mountains west of Mexico City do receive occasional snowfalls and their storms especially threaten the monarch butterflies from the eastern United States and Canada that have migrated south for the winter. Millions of them gather on those mountain slopes in the Oyamel fir forests. Visitors tell of forests colored orange with butterflies and background noise created by the fluttering of thousands of wings.


On March 2-3, 2001 a snow and ice storm killed modest numbers of monarchs at the main El Rosario and Sierra Chincua sites but devastated some of the smaller colonies a few miles away. An earlier cold snap had killed hundreds of thousands of monarchs at the San Andreas site. Originally thought to be the result of intentional spraying by loggers, it turned out that those too were victims of severe weather.


Unfortunately those storms of the 2000-2001 winter merely set the stage for an episode that took place this January.


Mid-winter in central Mexico is usually very dry but on January 11 a massive moisture-bearing weather system developed. Rain began falling the next morning and by the 13th four inches had been recorded in towns near the butterfly colonies. The rain then turned to snow and by that night two to four inches had fallen on the mountain forests.


The weather system moved on but that brought no relief to the butterflies. Temperatures the following three nights fell deep into the 20s.


The forests offer some protection from low temperatures to the monarchs but one site, El Rosario, is near cleared land and it was particularly affected.


By January 16, Lincoln Brower, who monitors the monarchs, reported that half of the El Rosario population had already fallen from the trees and others continued to drop. They covered the ground four to six inches deep, the majority of them dead or dying. Brower estimated monarch mortality at El Rosario and Sierra Chincua to be almost 80%. Although he was only able to monitor sites where about two-thirds of the butterflies winter, the massive character of the storm suggests that other sites suffered similarly.


Overall these figures suggest that more than 80 million monarchs died in this episode. (Numbers that large are hard to imagine. Hendrik Hertzberg developed an intereesting 1970 book entitled "One Million" to help us do so. It simply contained 200 pages with 5,000 dots filling each page. Arithmetic indicates that 80 million would call for 80 of those books or 16,000 pages.)


That's the bad news. No good news can balance that devastation, but it does offer some hope.


Monarchs have rebounded from massive losses in the past. Indeed, their 2000-2001 wintering population had reached an all-time low of just over 28 million, but after a remarkably good breeding year in 2001, about 100 million butterflies returned to the Mexican sites last fall.


Two things are evident from these figures. If the January storm had hit last year when the population was so low, it would have been even more catastrophic. And, although predictions for this year's breeding season are not as rosy, we can hope for another rebound in numbers.


And one other positive item: Our Agriculture Department has found that Bt corn is having no negative effect on monarch populations after all.-- Gerry Rising