Vanessa at night - migrations

[Paul Cherubini]

Ken Philip wrote:

Regarding my posting about the _Eurema lisa_ flight to Bermuda, Paul
Cherubini commented:

> Maybe the butterflies had been clinging by the thousands to nearby ships
> crossing the Atlantic and then left as Bermuda came into sight.

Let me add a bit to my quote from Scudder:

"...early one October morning several persons living on the northern side
of the main island of Bermuda perceived what they thought was a cloud
coming from the northwest, which turned out to be an immense concourse
of small yellow butterflies, which flitted about all the open grassy patches
and cultivated grounds in a lazy manner..."

We're not talking about _thousands_ here, but a much larger number. Either
there was a _gigantic_ fleet of ships out there, or Paul has seriously
dulled Occam's razor!
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OK Ken lets take a mathematical approach to the problem like Prof.
Bruce Walsh would.  Let's ask how many butterflies could conceivably
cling to the deck of an 1880's era ship?

According to my brief research, ocean freighters of that era typically
measured very roughly 400 feet x 60 feet = 24,000 square feet =
.55 acres = .222 hectares.   

Now at the monarch overwintering sites in Mexico there are
10,000,000 monarchs per 1 hectare so this works out to
2,220,000 monarchs per .222 hectares.

Now obviously there would be nowhere near the same surface area on
the deck of a ship as compared to a fir forest for the butterflies to
cling to, but even if the surface area was just 5% of what the forest
provides, that would still equal enough space for 111,111 monarchs!

Paul Cherubini

 
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