Migration strategies

[Anne Kilmer]

>
> I agree with Phil Schappert's definition. I think uni-directional movement,
> without a return trip, can be migration if it fits the definition. However,
> in that case the interesting evolutionary question arises: If migration
> occurs in only one direction, it is 100% fatal as far as the remaining
> portion of the population that did not migrate is concerned. So why would
> the trait of migration remain within the population?
>
 
because you never know ... it just might work. (remember that wonderful
imaginary oasis at the center of Antarctica, where there are songbirds
and flowers.) And besides, there's no point everybody staying in Palm
Beach County and fighting over the limited supply of milkweed.
 
The folks who study migration do not have all the answers. There are
very few of us out there watching the butterflies fly over.
I do not know whether the two cloudless sulphurs a day I see flying
eastwards through my back yard are the same two, who go home by another
path, or whether there is a continual supply of them.
When we see great swarms of butterflies all flying in the same
direction, we can feel fairly sure that this is migration rather than
dispersal.
Sometimes it makes no sense at all. Why do the whites fly *south* in the
springtime in Florida? Or do we see them drifting this way and that way,
and merely define their movement as southish.
Doubtless they've been tagged and studied and somebody knows all about
them. The
Maybe it all goes back to Pangaea, and their drift searches for another
continent, where things are better for butterflies.
 
The big-picture ecologists can probably work out elaborate dance
movements, according to the sprouting and blooming of host plants, the
changes in the weather, stuff like that. But the way we've gummed things
up, provided highways where the butterflies and birds can cross
mountains and their populations can mingle, created water sources in the
desert and so forth, changes are happening at an exponential rate.
Meanwhile, Mother Nature is not idle.
I suspect dispersal is a better word than migration for what most
butterflies do. I imagine southbound flocks of sulphurs and whites would
be a bonanza for southbound waves of migratory birds, and that it works
better to sort of sneak home through the shrubbery, unless you are
spectacularly toxic.
And I've seen a couple of those cloudless sulphurs downtown (perhaps
left from the Butterfly Ballot) but none in my yard yet this spring.
Anne Kilmer
South Florida
 
 
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