Date: 7/30/17 9:23 pm
From: Jim Anderson <jimnaturalist...>
Subject: [obol] Re: butterflies
Howdy OBLrs

The movement of the California Tortoiseshell butterflies is not (in my
opinion) a "migration" as such, but an "outbreak." I believe it's linked to
population dynamics of some kind, but not thoroughly understood. It
happened in Bend about 30-years ago, and unless research is carried
out annually within the tortoiseshell populations, it's probably difficult
to really put your finger on this or that cause.

Saying that, I also believe it's tied to nature's way of insuring survival
of a species. When weather and food plants are in balance, the butterfly's
larvae get what they need to develop the necessary chemicals
to metamorphose into adults successfully and then lay uncountable millions
of eggs; which in turn hatch and defoliate their food plants--which I have
a hunch is even good for the plants in some way. ,

In addition, while this is going on, the butterfly parasites also go into
supercharge mode and somehow have the ability to lay eggs on the jillions
of caterpillars. During the similar event some 30-years ago west of Bend,
we could actually hear the larvae munching on ceanothus leaves as they
defoliated all the bushes.

What was also unbelievable were the millions of chrysalis hanging on the
bare branches of the ceanothus. If you got close to them and stomped
your foot they would all begin to shake and clang like tiny bells. What a

We took 20 chrysalides home with us to photograph emerging butterflies.
However, if my memory serves me correctly, of the 20 chrysalides, 8 or 9
developed butterflies, but bright green adult wasps emerged from all
the others.

Another facet of an outbreak provides the species enough adults insects in
summer to go far from the "breeding territory" and pioneer new habitat,
further increasing the chances of the species to succeed even further.

During the outbreak some 30-years back I can recall the CA highway
department installing special truck washing equipment near Redding that was
used to wash smashed butterflies out of the radiators to keep
the trucks from overheating.

But now as I ponder on this magnificent phenomenon, on second thought,
perhaps the butterflies are just attempting to beat the hundreds
of thousands of humans predicted to be in Madras for the eclipse of the

Jim Anderson

On Sun, Jul 30, 2017 at 7:56 PM, Nicholas Mrvelj <nickmrvelj...>

> I spent some time in the greater Sunriver area myself this weekend. I can
> confirm seeing extraordinary numbers of California Tortoiseshells. During
> a hike around the Todd Lake area, we counted about 5-8 per second on
> average. All were heading in the same direction, often seeming to be at
> the mercy of the wind. Many perished on the roadways.
> Just south of Sunriver proper I saw 4-5 Common Nighthawks in flight each
> evening.
> Good birding,
> -Nick Mrvelj
> On Sun, Jul 30, 2017 at 6:09 PM Larry McQueen <larmcqueen...> wrote:
>> Ok, this is not about birds, but something to behold in the Cascades
>> right now. *Nymphalis* *californica*, the California Tortoiseshell, is
>> now doing a mass movement. I have been on a family trip this past week,
>> staying at Sunriver. We encountered thousands of these butterflies, first
>> near the top of the McKenzie Pass and again on the Cascades Lakes Highway,
>> south of the 3 Sisters. We found them in great numbers everywhere, all
>> seemingly flying in the same direction, maybe down slope. This had to be a
>> movement of the entire population (at least local), not millions, but
>> billions of this species. Pyle describes this phenomenon in “The
>> Butterflies of Cascadia”, as a release caused by a build-up of numbers over
>> years, and then followed by scarcity for years. I don’t know how well
>> studied this migration is, or where the butterflies end up.
>> This was not a birding trip, but I always love watching the Pygmy
>> Nuthatches. Crossbills were common around Sunriver. There was a single
>> Nighthawk on the entire trip, where there ought to have been many.
>> Larry

Please note my new email address: <jimnaturalist...>

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