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Articles : Snowstorm in Mexico

Multiple Authors

Chip Taylor

11 February 1996

On the 30th of December I received an e-mail message from a colleague concerning a news report on NPR (National Public Radio). This report described an unusual snowstorm at the Monarch overwintering sites in the Mexican states of Michoacan and Mexico and included claims made by local authorities that the a large proportion of the overwintering Monarchs were dead or dying as a result of the storm. Subsequent to this account there was a "blizzard" of news accounts, most of which repeated the same information. The following materials constitute a chronology of the best reports posted to our list, Dplex-L (edited for brevity) as well as some of the news accounts. As you go through this archive, you will see that there are several different interpretations of the significance of this event, although all observers seem to agree that continued logging within and near the roosting sites poses the greatest threat to Monarch populations. At this writing (11 Feb), the bottom line has not been written on this story and we expect to add a few more reports from visitors to the roosts. Monarchs should break from the roosts and begin moving north in late February and early March. The first Monarchs should reach Texas in the first week of March. Let's hope they reach Texas in large numbers and that a warm spring will push them north of the fire ant gauntlet which has developed in the southern states.

Posted to Dplex-L by Harold Spanier

1 January 1996

A freak winter storm was reported to have killed millions of Monarch butterflies. I've summarized three news items (from Canada)...

"Environmentalists in Mexico say a rare snowstorm in the western part of the country is killing millions of Monarch butterflies. A spokesman for the group of One Hundred (Mexico's principal environmental organization) says one third of the estimated 12 million Monarchs in the region could be dead by tomorrow. Nearly 18 centimetres of snow are already covering the ground and snow is still falling in five Monarch roost sites in the mountains."
Date: Dec. 30, 1995
Source: CBC AM Radio 21:00hrs

"Mexico: a freak snowstorm is killing millions of Monarch butterflies. An environmental group estimates 12 million butterflies will be dead by tomorrow. Scientists are on the scene, but there is nothing they can do"
Date: Dec. 30 , 1995
Source: CBC Television - Saturday Report

"Millions of Monarch butterflies killed by freak storm in Mexico"
Date:Dec. 31, 1995
Source: CJAD AM Radio 9:00hrs

Date: 01/03/96 Time: 08:46
Snow and Cold Kill Monarch Butterflies in Mexico

MEXICO CITY (AP) Snowfall and a cold snap have killed millions of Monarch butterflies at their wintering grounds in mountainous western Mexico.

A preliminary survey of the butterfly sanctuaries by researchers indicates at least 30 percent of the 50 million to 60 million Monarchs that migrated there from the United States and Canada perished, a leading environmentalist said Tuesday.

``This is just devastating,'' said Homero Aridjis, leader of the Group of 100 environmental lobby. ``The Monarchs dropped off the trees where they were perched and fell into the snow.''

He acknowledged the estimates were preliminary, but said the Monarch deaths could top 20 million from the two-day snowfall that began Saturday and was followed by a cold wave sweeping down from Canada.

High mountains covering some 6,400 square miles in Michoacan state west of Mexico City are a prime wintering ground for the vivid orange-and-black butterfly.

The Monarchs fly up to 3,100 miles south from Canada and the United States every year to winter in Mexico's evergreen forests. In those balmier surroundings, they don't dry out in their state of semi-hibernation. But the location leaves them vulnerable to cold in the higher elevations.

One English-language daily, The News, published a photograph Tuesday showing thousands of Monarchs littering a snowy mountain at a sanctuary called El Rosario, the only one opened to the public.

Reports said more than seven inches of snow fell over the weekend.

It rains often in the fog-shrouded mountains, but heavy snows come only every four to five years. The last big snowfall and cold wave, in February 1992, killed at least 70 percent of the butterflies wintering there, Aridjis said.

The rare winter snows increase pressure on the Monarchs, already hard hit by intensive logging that threatens their habitat.

The deaths of perhaps millions of butterflies will reduce the numbers that return to the United States in the spring.

But the delicate-looking butterfly is a hardy and fertile breed, and if conditions are right, they could replenish their numbers once they reach breeding grounds along the U.S. Gulf Coast and flow back across the United States into Canada.

There were conflicting reports Tuesday on the extent of the damage to the Monarch colonies.

``Some of them have died but it's only 8 percent maximum,'' said Homero Gomez, an agricultural engineer interviewed by the Mexican news network Televisa as he cupped a live Monarch in his hands.

He told Televisa that many of the Monarchs had withstood the cold by finding refuge in the thick forest.

``The Monarch protects itself,'' said Gomez in the footage, which showed Monarchs on snow-covered hillsides and tall evergreen forests shrouded in fog.

Lincoln Brower, a butterfly expert and professor of zoology at the University of Florida in Gainesville, said he will go next week to Michoacan and hoped to gather hard data on the number of deaths.

He said the extent of the damage remained to be seen, but that he could not rule out overlogging of the forests as making the butterflies more vulnerable to cold waves.

``The forest is an umbrella and a blanket and if you start poking holes in it by thinning the forest then you're asking for serious trouble when you do get these storms,'' said Brower, speaking by telephone.

He said hard scientific data is needed before a firm conclusion could be reached.

``For example, 1992 was a year when you had everything working against the butterfly: There were at least two weeks of overcast and wet weather so butterflies had gotten wet. Then it snowed and froze,'' he said.

He added that perhaps 4 million of the 5 million Monarchs in one spot alone had died that year, but that at least 20 percent recovered.

But he said the Monarchs proved to be a ``very resilient butterfly'' that flew back in lower numbers after the 1992 snowstorm and bred well in the Gulf Coast states on the return trip northward.

``Conditions for breeding that spring were good on the Gulf Coast so they managed to kick off a new spring generation,'' Brower said.

``The really bad scenario would be a big hit in Mexico from the weather followed by poor breeding conditions in the United States. Then the population could be knocked way back.''

Brower said there is no indication the Monarch population has declined over the decades but he predicted the whole migration could collapse in the next century perhaps even 10 years down the road if logging continued at its current rate.

``The wintering sites in Mexico are the Achilles' heel of the Monarchs because so few are left and they are really under pressure from the loggers,'' he said.

APNP-01-03-96 0844EST

The New York Times International

3 January 1996

Monarch Butterflies Killed by Snow in Mexican Winter Home

MEXICO CITY, Jan. 2 - The Monarch butterfly may look fragile, but underneath those fine orange-and-black wings is one tough customer. Every year Monarchs brave gales and downpours to waft from their summer haunts in Canada all the way across the United States to a winter refuge in central Mexico.

But Monarchs are not made to survive freezing snow. And on Dec. 30, in a rare cold spell, almost 12 inches of snow fell in the fir-topped mountain reserves where tens of millions of Monarch butterflies were clustered for their winter sojourn.

Mexican Government environment officials estimate that the freeze killed up to 15 percent of the Monarch population. But Homero Aridjis, a leading Mexican environmentalist, said the death rate could be as high as 35 per cent of the colony.

The new Monarch freeze is especially serious because it comes in the wake of an adverse migratory season for butterflies moving north from Mexico. There was a chilly spring and a dry, baking summer in the eastern United States, and American butterfly watchers noticed a thinning in the Monarch flocks.

"A combination of things this past year did not favor their reproduction," said Orley Taylor, an entomology professor at the University of Kansas and founder of a group called Monarch Watch whose volunteers around the United States track the butterfly's migrations. "The problem with natural history is that a couple of disasters one after the other can suddenly become devastating to a whole population."

In an astonishing migratory pilgrimage, Monarch butterflies that summer across Canada, Maine and the Great Lakes states all concentrate during the winter months in one region west of Mexico City, which straddles the states of Michoacán and Mexico. In 1986 the Mexican Government created five nature reserves in the area, on mountaintops at altitudes of about 11,000 feet covered with fir trees the Monarchs prefer.

This morning, in spite of rising temperatures, Government forest rangers and biologists who toured part of the reserves said there were snow banks densely littered with thousands upon thousands of frozen Monarchs, with many butterflies buried under the snow. According to a 1994 census, at least 60 million Monarchs live in the reserves.

A similar snowstorm in 1992 killed as many as 80 percent of the butterflies in some spots in the reserves, said one Monarch expert, Lincoln Brower, a zoologist at the University of Florida at Gainesville. The kiss of life caused an ebb in the Monarch migrations to the northeastern United States the next spring. Still, the Monarchs bounced back in 1993, Professor Brower said.

But butterfly scientists are concerned that the slow logging of the fir trees in the Mexican reserves, despite Government prohibitions, is leaving the Monarchs more vulnerable to severe storms and cold. Local farmers who make a meager living by selling lumber and firewood have continued to quietly cut the trees.

Professor Brower said his studies showed that rain-dampened butterflies were much more likely to die in freezing weather than dry ones. Also, the Monarchs tend to live in dense layers on top of one another on trees, and the butterflies at the bottom of the pile are more likely to survive than those on top. The loss of trees and their canopies make it more likely that the butterflies will be exposed to rain and snow.

"The more these forests are degraded, the more holes there are in their blanket," Professor Bower said.

Monarch Watch

4 January 1996

E-mail response to Riverside School, Greenwich, CT

Good Morning: Yes, there have been many winter kills at the roosting sites in Mexico in the past. Usually these killing snowstorms occur later in the winter and in 1992 there was a storm that killed approximately 70% of the Monarchs at one of the roosts. According to Bill Calvert, who has spent part of many winter seasons at the roost sites, a much more severe storm occurred in 1981. There was almost twice as much snow (13 inches) yet many of the butterflies buried in the snow survived because of the insulating effects of the snow cover. The temperatures which occur after the storms are apparently more important than the snow itself. Temperatures of -5 degrees C will kill the adult Monarchs in a relatively short time but they evidently can survive temperatures near freezing for many hours and perhaps even days. We still don't know the proportion of butterflies that died from this storm. The preliminary report was only an estimate and may have been exaggerated. Let's hope so.

Posted to Dplex-L by Monarch Watch

9 January 1996

The effects of the recent snowstorm in Mexico on the Monarch populations at the roost sites have been of some concern. The first reports suggested that mortality could be as high as 35% and this was followed by a number of other estimates that ranged from 3-15%. It has been difficult to evaluate these reports because it has not been clear whether those making the estimates were experienced Monarch observers and/or had actually made estimates based on some numerical assessment. Two messages were received today from Don Davis of Toronto and these messages contain new estimates from two long term Monarch observers, Jurgen Hoth and Lincoln Brower.

First message
Today, I received a telephone message and fax communication from Jurgen Hoth, Senior Program Officer at the World Wildlife Fund office at Oaxaca, Mexico. Based on past experience and current reports, he estimates that the mortality percentage from the recent snow storm falls in the vicinity of 5 - 7 %, and will be marginal on the overwintering population and migratory phenomenon. The Mexican Ministry of Ecology mortality estimates are also in the vicinity of 5- 7%.

In coming to this conclusion, Jurgen considered many factors, including the length of the storm and temperature factors. The storm only lasted 2 days. However, the rain before and after the storm may have heightened the impact. Lowest temperatures reached were reported to be -4 C. Under lab conditions, lethal temperatures were reached at -8 C. when dry and -3.3 C when wet (Calvert et al., 1989).

In 1981, a storm lasted 10 days, reaching temperatures of -5 C, and killed approximately 10% of the population in one colony site (Calvert et al. 1983).

Second message
Dr. Lincoln Brower was interviewed last night on the Canadian version of The Discovery Channel. He stated that his students in Mexico estimate the mortality rate at El Rosario to be in the vicinity of 10 - 20%.

He also noted that a number of apparently dead Monarchs had revived themselves (probably after warming up a bit) and were attempting to get back up onto vegetation.

Hence, it will be difficult to assess the real damage.

The New York Times Op - Ed

26 January 1996

Twilight of the Monarchs
By Homero Aridjis and Lincoln P. Brower

Homero Aridjis is president of the Group of 100, a Mexican environmental organization.
Lincoln P. Brower is a professor of zoology at the University of Florida.

As many as 30 million Monarch butterflies - perhaps 30 percent of the North American Monarch population - died after a snowstorm hit their sanctuaries in Mexico on Dec. 30. But storms are not the real threat to the Monarchs, which have wintered in the cold Mexican mountaintops for more than 10,000 years.

As is true for so much of besieged nature, the real dangers the butterflies face are man-made, in this case the destruction of the Oyamel fir forests in Mexico's central highlands.

About 90 percent of the world's Monarchs live east of the Rockies. Each fall, they migrate 2,000 miles from as far away as southern Canada to their winter quarters in the Oyamel forests - relict ecosystems of the Pleistocene era two miles above sea level. The Monarchs swirl down from the sky, festooning the boughs and trunks of the trees with layer upon layer of delicate wings, patterned in white, orange and black.

By early April, the eight-month-old butterflies migrate 800 miles back to the southern United States, where each female lays about 400 eggs on milkweed plants and then dies. The eggs turn into caterpillars, the caterpillars into jade-colored chrysalids etched with golden crowns. When they hatch, this spring generation travels 1,000 miles north to Canada. Over the summer, two or three more generations of butterflies are produced, and the great-grandchildren of those that flew north return to Mexico to repeat the cycle.

But the monarch's existence is threatened by the cutting of the remaining Oyamel forests. When intact, a forest serves as an umbrella and blanket, protecting the butterflies from freezing rains. The logging creates gaps that allow rain and snow to fall through the forest canopy and onto the butterfly clusters. As the weather clears, the life-sustaining heat radiated from the butterflies' bodies leaks out through these holes in the blanket of trees and the Monarchs freeze to death.

Nearly two decades of conservation efforts by private organizations in Mexico, Canada and the United States - as well as a 1986 order by then President Miguel de la Madrid to protect five wintering enclaves - have done little to stop the destruction. The Mexican Government continues to permit logging in protected and unprotected areas. Illegal commercial cutting is rampant. Local peasants harvest trees for fuel and building materials, and cattle trample and eat the fir seedlings.

It is not too late to undo the damage. The Mexican Government and international conservation groups together should buy or lease the forests from the peasant communities, which are now allowed under Mexican law to sell their communal lands. This must be done quickly: Loggers are lobbying the Government to open up about 25 percent of the protected areas. The land could be bought for about $60 million, a small price in light of what is at stake, environmentally and economically.

Whereas logging is a one-shot deal, the local people could benefit indefinitely if they had help to create high-qulaity ecotourism ventures. To plan and pay for such projects, Mexico and private environmental groups and foundations need help from the United States and Canada. The three countries should be partners on environmental issues that affect all of them, in keeping with the side agreements to the North American Free Trade Agreement.

Can trilateral cooperation save the Oyamel sanctuaries? Or will North America let the forests fall and these majestic butterflies disappear?

Posted to Dplex-L by Monarch Watch

4 February 1996

Although there have been numerous accounts in the press about the devastating effects of the December snow storm, three recent visitors to the El Rosario roost, Jane Ruffin, Harold Spanier and Brian Visser, report that the number of live Monarchs at this roost are extraordinary. The numbers of dead butterflies on the forest floor beneath roost do not seem to be excessive and guards at El Rosario are quoted as saying there are more Monarchs at this site than last year. If true, this is surprising since the Monarch population originating from the northeastern US and CA was extremely low last fall. Also, Bill Calvert reported that the numbers of Monarchs at El Rosario were larger than normal in 94-95.

Posted to Dplex-L by Monarch Watch

6 February 1996

The following messages concern the mortality of Monarchs observed by two Monarch experts, Walter Sakai and David Marriott, at El Rosario. These messages have been edited and only those portions which pertain to the numbers of Monarchs and the mortality at El Rosario have been copied. Disagreement continues on the extent and causes of the mortality but there seems to be universal concern about the tree thinning within roosting sites and the surrounding forests. Thinning the forests increases the degree of reradiation (heat loss) at night, lowering the temperatures around the clustered butterflies. The concern is that decreased temperatures and increased exposure could put the Monarchs at greater risk during snow storms in this region which are often preceded and/or followed by cold rains.

Walter Sakai:

Visited the El Rosario Site on 02 Feb 1996. Monarchs were extremely high up the hill, above the "meadow." Very few were flying about. For those familiar with the site, the clustering was located in the vicinity of "8" on the upper loop trail. Access through the clusters was restricted, so it was difficult to estimate the extent of the colony and its size. There was no sign posted indicating the population size.

Mortality was minimal. I would estimate that there was 2-3X more mortality when I visited the site at about the same time 2 years ago. I looked at "intact" dead Monarchs and estimated that 30-40% of the intact Monarchs were killed by the snow. I defined snow mortality as dead intact Monarchs that showed no indication of predation (no abdomens slit, body intact, etc). Adding that percentage to the wings littering the ground, I would estimate "snow" mortality to be about 15-20% of the dead Monarchs.

Now what that percentage (15-20%) relates to the entire colony is hard to gauge since we were not able to see the entire colony and no estimates were posted. David Marriott talked to some of the Mexicans who said mortality was only 5% of the colony.

Of course, this is one site, estimates are crude, and I have been to the site only a half dozen or so times.

In a second message which mostly repeated the first Walter said: From my vantage point, the colony looked quite large. But I can not make an educated guess as to its size.

David Marriott:

I would like to make some brief comments on Walt's observations. Regarding his statement: " I looked at 'intact' dead Monarchs and estimated that 30-40% of the intact Monarchs were killed by the snow." Walt later points out that, "I would estimate 'snow' mortality to be about 15-20% of the dead Monarchs." Walter's visits to El Rosario include one in 1994, one in 1992, and one (two visits) in 1989. His estimates are profound and misleading.

Local volunteers (ejidos), affiliated with the government of Michoacan, have been calculating the mortality rate at El Rosario by examining dead Monarchs in areas measured by square meters. Their data shows that 95% of Monarchs die by predation (mostly birds) and less than 5% from the snow fall of December 19 to January 19. I can assure all of you that the snow fall had little effect on the mortality of Monarchs at the El Rosario site. I have never seen so few Monarchs dead on the ground, and I visit the site and talk to the natives two or three times a season.

We need to pay more attention to sites that are being destroyed by tree cutting. The El Rosario Site is an example of preservation by profit.

Posted to Dplex-L by Lincoln Brower

7 February 1996

This is just a note for regarding what is happening at the Monarch colonies in Mexico this overwintering season. First, if the El Rosario colony is really larger than usual this year, it may be because more Monarchs are being forced to concentrate in fewer colonies due to degradation of the outlying colonies that are not protected. Secondly, low estimates of dead butterflies on the ground can result from the colonies moving away from where they initially formed in November. When I was at the Sierra Chincua on 11 January 1996, the colony had been badly impacted by the 31 December 1995 storm. Evidence for this was the low density of Monarchs in the colony and the degree to which the butterflies had scattered after recovering from the stormy period. I observed huge flights of butterflies around the western edge of the colony which I interpreted, tentatively, as recovering Monarchs moving into a more sheltered area of the Oyamel forest.

Two of my students are currently estimating the mortality caused by the storms, as well as measuring the sizes of the colonies, and we should have the data by the end of the season in March. So, I urge all of those interested not to jump on the various guesstimates or necessarily believe what you see; things are more dynamic than they might seem...and there appears to be a lot of political pressure on the guards at Rosario to minimize the damage as when they talk about it to the tourists visiting the area. We need scientific objectivity in tracking this situation.

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