Do Monarchs need Mexican forests?

[Paul Cherubini]

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: