> We acres of milkweed but no Monarchs this year. I think Monsanto has
> killed them all.
The overall trend line would be affected by that, but from one year to
the next, it really is a very very small incremental change. A major
population crash like this would be caused by a localized or regional
event that catches them while they are concentrated in a tight area.
Last winter, the population in Mexico was severely down (somewhere
around 50% from normal). And this year it only got worse. Most people
are looking at the drought in Texas as being the primary culprit.
Just to illustrate how vulnerable they are, during migration and
wintering over, the are known for their concentrations in trees. One
single tree could theoretically hold every successfully migrated
Monarch from an entire state. ONE!
When we lived in Newton, IA, it was pretty fascinating how a couple of
migratory birds would use our town for their stopping over point. They
would follow the highway south and then used I-80 as their stopping
point. Nothing too unusual there. But what was unusual was that they
concentrated in our subdivision and ONLY in our subdivision. One block
east of our house? Nothing. Other side of I-80? Nothing. Three blocks
north? Nothing. Other side of Highway 14? Nothing. Every year, the
same thing. The noise was so great that it actually blocked the
highway sound. There were so many birds in the trees that the branches
sagged. Each tree held thousands of birds. Year after year, the same
thing happened. The long time locals said that prior to I-80, they
would continue south another 20 miles to the banks of the Des Moines
river. Once I-80 was built, they started using Newton as a stop point
and used the orchards SW of town for their trees. The orchards are no
longer there, but a subdivision is. I saw them rise en mass once and
thought it looked a bit apocalyptic. I was thinking that this was in
the core of their central flyway and represented a significant
percentage of all of them. One localized disaster and it would have a
measurable impression on the entire population. They'd be there for
only a few days, waiting for the stragglers to show up and rest. Once
everybody was there, a mass ascension would occur and they would be
gone. One day, my wife called me up and said "what's that sound?" A
shrill drone just echoed through the house and I could even hear it on
the phone.
AG
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