Do Monarchs need Mexican forests?

[Patrick Foley]

My understanding (only from quotes in the popular press) is that Brower
made his mortality estimates after the those of Solis and others, and
thus obtained higher estimates. Brower also thinks the uncertainty
around Monarch overwintering estimates is enormous.

Again, I would like to see the scientific papers that show how these
estimates are made. I still have little idea how trustworthy any of the
estimates are. Any practicing population biologist would be wary about
an estimate without a standard error. And any scrupulous person would
want to know more before he attacked the honesty of others. The evidence
from the popular press is that Brower made his estimates using some kind
of standard (over several years) approach counting dead butterflies per
quadrat and comparing the dead to population size estimates. This does
not show that his estimates are right, but it does suggest that he is
not just dreaming them up to drum up hysteria in the press.

Brower may well be wrong about his mortality estimates. But the popular
press articles I have seen clearly show that he is uncertain about
Monarch numbers. Paul, are you certain about your numbers? Do you think
anecdotal evidence and carefully chosen photographs are an honest
improvement over Brower's scientific papers?

Patrick Foley
patfoley at csus.edu

Patrick

Paul Cherubini wrote:

> Patrick Foley wrote:
>
> > 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?
>
> Yes, the two groups (American vs Mexican biologists) measured
> mortality at the same locations and the same times, but I don't
> know anything about the techniques they used.
>
> However we can review some basic monarch census data ALL
> the monarch authorities agree on.
>
> 1. In the winter of 2000-2001 the overwintering monarch
> population in Mexico was 28 million butterflies.  In the spring of
> 2001 ALL monarch authorities agree the size of the migration
> that arrived in Texas from Mexico was very small. Mike Quinn
> described it as "barely perceptible" to a Fort Worth, Texas
> newspaper reporter.
>
> 2. Just 9-10 months later, in the winter of 2001-2002 the
> the overwintering monarch population in Mexico was 110 million
> butterflies - 3.93 times as large as the overwintering population
> in 2000-2001 (and about 40% above the long term average
> of about 76 million butterflies).
>
> Now if Lincoln Brower is right and 75% of these 110 million
> monarchs perished in the January freeze then only 27.5 million
> monarchs would have survived.  And it would follow that the
> size of the spring migration that arrived in Texas this past
> March and April should be near the "barely perceptible" levels
> that were observed last year.
>
> Now if the Mexican biologists are right and only 30% of these
> 110 million monarchs perished in the January freeze then
> 77 million monarchs would have survived.  And it would follow
> that the size of the spring migration that arrived in Texas
> this past March and April should be about 2.75 times as
> large as the numbers that were observed last year in March
> - April.
>
> Well, ALL Texas monarch authorities agree there are alot more
> monarchs in Texas and neighboring states this spring compared
> to last year. (And to my knowledge not a single monarch
> authority has put out a press release announcing this fantastically
> good news).
>
> Here are just two examples:


 
 ------------------------------------------------------------ 

   For subscription and related information about LEPS-L visit:

   http://www.peabody.yale.edu/other/lepsl