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Monarchs Are Not on the Road to Recovery

By Bill Freese, Science Policy Analyst, Center for Food Safety

March 30, 2016
Center for Food Safety

Endangered Species Act protection essential to monarchs’ survival

Much as we’d like to believe this year’s upswing in monarch population numbers is the start of a recovery, it’s most likely a passing fluctuation due to unusually favorable weather conditions.  The long-term outlook remains bleak, as indicated by a recent study that predicts an 11 to 57% chance of extinction for the monarch migration over the next two decades.  Efforts to restore habitat are welcome, but they haven’t begun to reach the scale necessary for a true recovery.  The still small size of the monarch population makes it more vulnerable to severe weather events, such as the unusual winter storm in early March that has killed a substantial though yet unknown number of overwintering monarchs in Mexico.

In 2014, monarch advocates led by Center for Food Safety filed a petition to list the monarch as “threatened” under the Endangered Species Act (ESA).  The U.S. Fish and Wildlife Service (FWS) agreed in December 2014 that ESA protection may be warranted, but then failed to make a final decision by the ESA-prescribed 12-month deadline.  Accordingly, advocates were compelled recently to seek a court-imposed deadline for the Service to make its determination.  Protection under the ESA is essential to ensure the monarch’s survival.

Monarch lovers across North America know that this is the season for counting their favorite insect.  Come winter, monarchs east of the Rockies gather together in oyamel fir forests in the mountains west of Mexico City.  Impossible to count when flitting about in the summer, monarch numbers can be estimated quite well based on the area of forest they occupy in winter.

The latest count came out less than a month ago.  Monarch overwintering habitat (and hence numbers) more than tripled over last year, from just over one to four hectares (2.8 to 10 acres).  Based on this upswing, NPR declared “Monarch butterflies are on the rebound,” while others claimed that a “recovery” or “big comeback” is underway.  The monarch population has reportedly “soared,” generating “enormous enthusiasm” and providing cause for “celebration.”

To be fair, these articles do sound notes of caution.  But the overall impression is one of unbridled optimism and success.  As much as we welcome the news of a larger monarch population this year, it is far too soon to declare that monarchs are on the road to recovery.  A recent event and a just-released scientific paper confirm our skepticism.

Scientists with the U.S. Geological Survey teamed up with monarch experts to assess the extinction risk for monarchs.  Over the next twenty years, they predict an 11% to 57% chance that monarchs as a migratory species east of the Rockies will go extinct.  The precipitating event, they explain, could be “catastrophic mortality while overwintering in Mexico.”  As if on cue to dramatize the lesson of this study, on March 8th the monarch colonies in Mexico were hit by an unusual winter storm.  Heavy rain, snow, high winds and low temperatures have combined to kill off a substantial number of overwintering monarchs.  It’s too soon to know how many died.  Estimates range from several million to 35% of the population, equivalent to many tens of millions.

So before we begin celebrating, let’s consider two key questions.  How significant is this year’s count?  Does it have anything to do with habitat restoration efforts?

The trend counts more than annual counts

The graph shown below puts the 2016 upturn in context.  It shows that huge annual fluctuations are the norm, and that a good season or two means very little.  In fact, there have been virtually the same number of year-to-year upswings (11) as downturns (10).  Despite this, monarchs have declined steeply over 22 years, and the four years with the fewest monarchs ever recorded have all occurred since 2009.  The graph’s red curve is one way to portray the decline, called exponential regression.  It represents the statistically significant trend-line that best fits the annual count data – the most balanced way to smooth out year-to-year fluctuations.  By eliminating this “noise,” the regression gives us a truer picture of what’s happening to monarchs over the long term.  Based on it, monarchs have declined on average 9.2% a year, or by 87% since 1995.  And that’s even after one accounts for this year’s much-heralded upturn.  Still feel like celebrating?

Source data:, last visited 3/11/16.  The years on the x-axis (e.g. 1995) represent the overwintering season that begins with that year (e.g. 1995/1996).  The red curve is an exponential regression: A = 13.668 x EXP(-0.096 x Y), where A = the area along the regression curve and Y = year (1994 = 1, 1995 = 2, etc.).

Why do monarch populations fluctuate so much?  We don’t know all the reasons, but weather is an important factor.  Dr. Chip Taylor of Monarch Watch notes that later-than-normal spring arrival of monarchs in Texas, likely weather-related, has been associated with population upturns in 1996, 2005, 2010, and 2015 as well.  Weather extremes can have the opposite effect.  A single winter storm in Mexico in 2002 destroyed up to half a billion monarchs, over three times the entire current population.  And as noted above, a storm in early March killed a substantial number of monarchs, though it’s too soon to tell how many.  High temperatures and drought in the U.S. breeding grounds can also knock back the population. 

Why are monarchs in long-term decline?  Extreme weather comes and goes, but habitat loss puts unremitting downward pressure on the population, limits the size of any rebound, and is difficult to reverse.  Summer habitat is particularly important: milkweed family plants for food and breeding purposes, and nectar-producing plants to feed adults.  Common milkweed has been decimated in Midwestern cropland by widespread use of the herbicide glyphosate on genetically engineered corn and soybeans.  Monarch habitat is also lost to urban sprawl and other development.  Illegal logging in Mexico has been slowed, but continues to degrade the monarch’s overwintering grounds.

If changeable weather conditions generate the wild annual fluctuations, habitat loss is the major factor behind the long-term decline.  Climate change, disease, predators, and other pesticides are additional threats.

Is habitat restoration behind the 2016 upturn?

The media seem convinced that milkweed plantings begun by government agencies last year are contributing to the monarch’s “recovery,” but this is almost certainly not the case.  The major reason is that milkweeds thus far restored are an infinitesimal fraction of those lost over the past two decades.  The U.S. Fish and Wildlife Service announced that it restored 0.25 million acres of milkweed last year.  This might sound like a lot, but it’s just 0.15% (just 15 one-hundredths of 1%!) of the estimated 167 million acres of monarch habitat lost over the past two decades.  Besides restoring lost habitat, we must also make good the ongoing loss of milkweed to development, which has claimed 1.4 million acres per year since 1982, some portion of which once harbored milkweed. 

Annual fluctuations no excuse for denying monarchs legal protection

In 2014, Center for Food Safety (CFS) and allies, including renowned monarch scientist Lincoln Brower, petitioned the U.S. Fish and Wildlife Service (FWS) to protect monarchs as a threatened species under the Endangered Species Act (ESA).  In December 2014, FWS determined that protection may be warranted, triggering a public comment period and an official review that by law was to be completed within 12 months.  The Service just missed the statutory deadline for making a final determination, compelling monarch advocates to seek a court-imposed deadline for the Service to issue a decision.  ESA protection would entail a strong, legally enforceable monarch recovery plan, including protected habitat, and is essential to ensure the butterfly’s survival.  Annual fluctuations such as this year’s uptick in monarch numbers must not be used as a pretext for the Service to deny monarchs the strong legal protection required for a true recovery.

What a credible monarch recovery plan must include 

The Midwest has lost about one billion milkweed plants this century, a decline of 64%, most of it from cropland sprayed with glyphosate.  Milkweed growing amidst corn and soybeans produces nearly four times more monarchs, plant for plant, than milkweeds growing elsewhere.  This is why widespread restoration of milkweeds to crop fields provides the best monarch bang for the milkweed buck.  Programs to incentivize farmers to integrate prairie strips that include milkweed in their fields would be the best way to accomplish this.  Because prairie strips also inhibit soil erosion and agrichemical runoff, they constitute a win-win-win solution for monarchs, farmers and the environment.  Restraints on intensive use of herbicides with genetically engineered crops would likely also be required.  While USDA has tiny programs in place to promote pollinator habitat that can include milkweed, much more needs to be done.

Summing up

One year’s upturn in monarch numbers does not a recovery make.  Of much more importance is the long-term trend, which still shows steep decline.  Efforts to increase monarch habitat – while admirable – have thus far restored only a tiny fraction of the milkweeds lost over the past two decades.  Vigorous restoration of milkweed to cropland in ways that benefit farmers and the environment as well as monarchs is an indispensible part of any credible monarch recovery effort.  The best prospects for implementing this and other effective measures to ensure the butterfly’s survival is listing the monarch as a threatened species under the Endangered Species Act.

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