migration book review

Paul Cherubini monarch at saber.net
Sat May 12 14:44:26 EDT 2001

Bill Cornelius wrote:
> Hey y'all:  here's a review of a book about monarch migration:
> http://www.globeandmail.ca/gam/Science/20010512/BKBFLY.html

In the review, it says the author, Sue Halpern wrote:

> We don't know how the monarchs know where to go, we
> have no idea how they navigate the annual route along
> identical flight paths, right down to resting on the
> same trees in the same fields year after year. And we don't know how
> they pass on the knowledge of these routes to the future 
> generations that make the return trip.

This book glamourizes the monarch migration instead of giving the public 
all the facts. The facts are that while about 1 in every 70 monarchs tagged 
in the midwestern USA are recaptured at the overwintering sites in Mexico, 
only 1 in 200 monarchs tagged in the eastern Great Lakes area are recaptured 
in Mexico and only 1 in 800 monarchs tagged along the east coast are recaptured
in Mexico.  These data suggests a majority of east coast monarchs never end 
up in Mexico and thus are not displaying "miracle" navigational capabilities.
It is unlikely that east coast monarchs suffer alot more mortality because the 
flight distance (whether straight line, elipitical or great circle) between New Jersey
to central Mexico as compared to Minneapolis and central Mexico is only 
about 20-25% longer.

Also, we know tagged monarchs released at the same location,
date and time disperse in a wide range of directions and end
up at overwintering areas 1,500 miles apart. This map
http://www.saber.net/~monarch/NorthAmerica.jpg for example, shows
what happened to monarchs released in Albuquerque, New Mexico
Silver City, New Mexico, Evanston, Wyoming and western Colorado.

> it [Sue Halpern's book] also focuses attention on environmental issues
> plaguing all three countries: 

> * Toxins from genetically modified food crops are landing on the milkweed 
> plants upon which monarch larvae feed, killing the insects.

> * Intense logging in the Transverse Mountains is destroying monarch habitat.   

> * Mexican farmers are threatening that if these reserves aren't re-opened to
>  logging, Michoacán might become "the next Chiapas."   

> * ecotourism might be trashing the reserves anyway.   

As we saw yesturday, the complete truth is that scientists have found Bt corn actually 
makes good monarch breeding habitat. Scientists have never found dead monarch 
larvae on milkweeds growing in Bt corn fields.  Only a trivial amount of logging in
taking place in the monarch overwintering area in Mexico and nearly all these forests
have been selectively logged for centuries. There isn't a single mountain in Mexico
where the butterfly population has declined since the colonies were discovered in 1975.
The has been no poisoning of the butterflies by loggers or farmers. Ecotourism has
had no significant adverse impact on the butterflies or the environment at the Mexican 
overwintering sites - the tourists are there only for 4 months of the year so the tiny
amount of trampled vegetation has 8 months to recover. Monarchs can overwinter 
successfully in 100% artificial, man made habitats in some of the  
most intensely urbanized areas of North America: 
http://www.saber.net/~monarch/Picture%208.jpeg. In fact, 90%
of California's top 40 largest monarch overwintering sites are located in man made 

Paul Cherubini, Placerville, Calif.


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