Do Monarchs need Mexican forests?

Patrick Foley patfoley at
Fri Apr 19 01:29:58 EDT 2002

Paul and others,

Two points about Paul's latest attacks on Lincoln Brower:

1) Brower et al 2002 April Conservation Biology cite the following papers (and
others) which they believe demonstrate that Monarchs do get protection from

Anderson, J. B. and L. P. Brower 1996. Freeze protection of overwintering monarch
butterflies in Mexico: critical role of the forest as a blanket and an umbrella.
Ecological Entomology 21: 107-116.

Brower, L P 1996. Forest thinning increases monarch butterfly mortality by altering
the microclimate of the overwintering sites in Mexico p 33-44 IN S S Ae, T
Hirowatari, M. Ishii and L P Brower (eds.) Proceedings of the international
symposium on butterfly conservation, 1994. The Lepidopterological Society of Japan,

It appears to me that Brower is doing research, reporting that research in journals
and undergoing the scrutiny of reviewers. If you think he is wrong, why not do some
research and publish it. More physiological abd behavioral research would be
welcomed by everyone. This appears to be a scientific disagreement (not a lobbying
issue) so let us settle the science.

2) As a population biologist I am very interested in the statistical techniques
used to estimate Monarch overwintering mortality. What techniques did Brower use to
get 74% mortality. What techniques did the others use to get 33-47% mortality? What
were the standard errors of these estimates? Did they refer to the same locations
at the same times? If you know the answers, we could all benefit. This appears to
be a scientific disagreement (not an attempt to frighten butterfly-fanciers), so
let us settle the science.

Patrick Foley
patfoley at

Paul Cherubini wrote:

> Chuch Vaughn wrote:
> > Any scientist who engages in "crisis" reporting has crossed the
> > line from scientist to activist.
> Chuck, on the Ecolog-l  a few weeks ago C.D.Basset made a similar
> comment:
> "When a "scientist" distorts or misuses his or her data, they are no
> longer acting as scientists but as political operatives. It is appalling
> to hear "scientists" consider when it is okay to distort data!
> Chuck, I now wish to examine once again what happened with the monarchs
> in Mexico this past winter - this time in a show and tell kind of way that
> demonstrates how the facts about what really happened have never
> been revealed to the public:
> First there were Elizabeth Howard's reports on Feb.7 & 14 on the
> Journey North website announcing that Lincoln Brower had
> determined that over 75% of the entire overwintering population
> in Mexico was wiped out.
> Howard also
> explained that while scientists had not yet visited certain outlying
> colony sites, mortality rates were feared to be similar because
> "their forest habitat is less pristine"
> In addition, Elizabeth Howard wrote about how the "storm illustrates
> the danger of heavy deforestation" and "because
> of heavy deforestation, scientists fear the remaining forest may no
> longer provide the protective microclimate needed to keep the
> butterflies suffieciently dry and warm."
> Likewise Lincoln Brower told the World Wildlife Fund "the forest
> canopy was too thin to protect the delicate monarchs from the rain and
> cold weather last month"
> I noted to myself that conspicuously absent from these sensational
> reports was hard evidence - actual pictures of the thinned forests
> that were supposidly no longer capable of keeping the butterflies
> sufficiently warm and dry.
> So I visited the sites and took myy own pictures. Mexican biologist
> Eligio Garcia led a group of us to the "monarch cemetery" at the Sierra
> Chincua colony where Brower said 74% of the monarchs had died.
> Instead of finding a thinned, "degraded" forest, I found this:
> I found the butterflies littered the ground below a very tall and
> dense forest - the same exact forest Brower had said "was
> too thin to protect the delicate monarchs from the rain and
> cold weather."
> Next, I wondered if the scientific literature supported the
> notion that an "intact" forest was capable of keeping the butterflies
> "sufficiently warm and dry."
> I found exactly the opposite.  In 1983 Dr. Bill Calvert coauthored a
> a paper with Lincoln Brower in Biotropica in which they described
> their  experiences while camped out with the monarchs for several
> days during a major snowstorm in Jan. 1981 at the Chincua colony
> in a forest they consider "intact".  Some key points they made
> were:
> "In general, butterflies in branch clusters are less shielded from the
> wind and soaking action of precipitation than those in trunk clusters
> and are therefore more likely to be wetted by precipitation. Indeed
> some branches that came down contained butterflies that were
> soaked with water."
> "it is clear from this study that forest cover is not sufficient to
> protect all butterflies within a colony from occassional winter
> storms"
> Next, I wondered if there was any field evidence to support
> Elizabeth Howard's (Journey North) speculation that there had
> been heavy mortality at some of the  outlying monarch colonies
> - the ones she claimed had "a less pristine forest."
> Here again, contrary to the scientists' predictions, reports began
> coming in about how two outlying colonies (Piedra Herrada & Cerro
> Pelow) were not hardly damaged by the Jan. 2002 storm.
> Here's are two of these reports from Dr.Bill Calvert
> and one from Dr. Robert Cook, a Wildlife Biologist for the National
> Park Service:
> "While the reports of the high mortality at El Rosario and Sierra
> Chincua are certainly cause for grave concern, I wanted to let you
> know that this extreme mortality event may not have affected all
> overwintering sites. We saw no evidence of die-off, there was only
> what I would consider "background mortality", evident in the relatively
> small numbers of dead butterflies we saw on the ground."
> Lastly, I wondered if the Mexican monarch scientists agreed with
> Dr. Brower's and Journey North's claims that "over 75% of the entire
> overwintering population in Mexico " had been killed.
> I found out the Mexican scientists (Eligio Garcia and Dr. Roberto
> Solis) felt Brower had vastly exaggerated the mortality estimates.
> Their findings were that 33-47% of the monarchs at the Chincua and
> El Rosario colonies perished in the January storm, not 74-80% as
> reported by Brower.
> In Summary, what actually happened was this:
> 1. There was heavy, though not truly catastrophic mortality at the large
>     Chincua and El Rosario colonies.  Heavy mortality occurred at Chincua
>     despite the fact that it was located in an especially dense, intact forest.
> 2. There was light mortality at some outlying colonies even though
>     these forests were claimed by Journey North to be "less pristine"
> 3.  If the mortality estimates of the Mexican scientist's are correct,
>      only about 30% of the entire overwintering population perished
>     in the January storm, not "over 75%" as reported by Lincoln
>     Brower and Journey North.  The strong monarch migration that
>     has occurred in Texas this spring suggests the mortality estimates
>     made by the Mexican scientists were more accurate.
> The American public will never have the opportunity to know these
> findings because the American monarch scientists and Journey North
> are unwilling to put out mass press releases or even web site information
> retracting much of what they had said earlier and unwilling to provide
> reporters with photos showing how contrary to their expectations,
> there was heavy mortality in some dense forests and light mortality in
> some "less pristine" forests.
> Paul cherubini
> Placerville, Calif.
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