"dire straits faced by most of our butterfly fauna"

Paul Cherubini monarch at saber.net
Sun Apr 29 04:06:14 EDT 2007

Dr. Arthur M. Shapiro, professor of Evolution and Ecology at UC Davis,
is in the news this Spring again with yet another doomsday newspaper
article in regards to butterfly abundance and diversity in the southern 
Sacramento Valley of California:
This time Shapiro fully authored the article so there can be no doubt
about what he said or meant.

Professor Shapiro's article is abundantly laced with worrisome, 
emotion stirring terminology and phases like: "serious trouble", "most 
alarming trend", "last year was catastrophic","dire straits", "grim 
outcome", "obviously in trouble", "most likely villain",
"is the crisis over? Hardly.", "highway to Hell." See below. 

Drought not all bad for butterflies
Article Created: 04/29/2007 09:46:18 AM PDT

Butterflies in our part of California have had some tough times lately.
Most people say there aren't as many butterflies now as there were
when they were kids. Because I've been monitoring butterflies on a
biweekly basis at up to 10 sites in this part of California since 1972,
I was in a position to say whether or not that was true. And by and
large, it wasn't. I used to argue that butterflies are just more
conspicuous to kids than to adults, and it was all just a matter of
perception. Until 1999, that is.

In 1999, more than a dozen species in our area showed a sharp
downturn. I began to sit up and take notice. Was something actually
going on? In a word, yes.The North American Butterfly Association
sponsors a Fourth of July butterfly count modeled on the Audubon
Christmas Bird Count. This is a free-form, rather unconstrained
activity, and it's questionable what, if anything, the data it generates
 can tell us about trends in butterfly numbers or diversity. But since
 the '70s I had been doing my own count right here in Davis, and
it was completely standardized in methodology - so it was potentially
informative. The question was, what if anything can one day's
sampling a year tell us?

Several years ago a group of us set out to explore that question,
using a variety of statistical tools. One of them was a diversity
measure called "Fisher's alpha," brought to our attention by
Professor Michael Rosenzweig of the University of Arizona.
There were no grossly obvious trends in the data set, but when
it was analyzed using Fisher's alpha, a grim outcome resulted.
The analysis told us we were already experiencing a decline
 ("subclinical," in epidemiological parlance), and it was likely
to accelerate to the point where it would become obvious.
Well, in 1999 it did. But in retrospect, we can see signs of it
already in 1998.

Most of the species that went downhill in 1999 recovered to
some degree in subsequent years, but not completely, and
some began drifting downward again. The most alarming
trend was the loss of common, weedy species - the antithesis
of the stereotypical endangered super-specialist. The Large
Marble butterfly disappeared from one after another of my
long-term sites, despite the fact that it breeds on weedy
mustards and wild radish, which are not exactly in short
supply. The Common Sootywing breeds on amaranth
pigweeds and garden cockscomb and was in every weedy
 yard and vacant lot in Yolo County (it doesn't occur in

It disappeared from all my sites but one. Some of the other
species obviously in trouble, while not weedy, had been
superabundant not so long ago and hardly seemed good
candidates for extinction. The Willow Hairstreak used to
swarm by literal millions along Putah Creek on the Valley
floor. Now it was gone - completely gone.

Meanwhile, several billion migrating Painted Ladies originating
 in the waterlogged deserts of Southern California filled our
 skies in the spring of 2005, masking from the general public
the dire straits faced by most of our butterfly fauna.

When we did statistical analyses comparing butterfly trends to
climatological data, we got no consistent patterns. Some
climatic variables were better correlated with the trends than
others, but their relative importance was inconsistent from
place to place as well as from species to species. At any rate,
correlation does not prove causation. "Green" folks were
quick to suggest agrochemicals or genetically-engineered
crops were behind the declines, but they did not "fit" the
picture well.

For example, despite all the hoopla about BT corn pollen
being toxic to Monarch butterfly larvae, not only had there
never been any convincing evidence of impacts in the field,
but there wasn't any BT corn here anyway and besides,
the pollination season didn't mesh with the life cycles of
most of the declining species.

The most likely villain seemed to be the changing pattern of
land use in our region, and especially the loss of connectivity
among habitat patches. That's what we're working on now.

Meanwhile, the weather in late winter and spring 2006 was just
about the worst possible for butterflies in the Central Valley - cool,
 cloudy and very wet. Areas of the Yolo Bypass and the
American River floodplain remained under water into June! Last
year was catastrophic for many butterflies, and for the species
already in decline it appeared to be the coup de grace. It looked
like a substantial number of species had been lost, perhaps even
regionally. In 2006 there weren't even any significant numbers
of Painted Ladies; it was a very dry year in the desert.

Well, it's been a dry year here in water year 2006-07. So dry, in
fact, that the Yolo Bypass never filled up with water. Even the
vernal pools never filled up with water. Drought may be bad for
Painted Ladies in the desert. But the winter of 2006-07 brought
a miraculous rebirth to our moribund butterfly fauna! Species
that seemingly had disappeared were back, sometimes in quite
respectable numbers. Some things, including the Large Marble,
 were seen at some localities for the first time in five or six years.
The Purplish Copper, which had been on the skids, had a very
good summer in the Yolo Bypass in 2006. It normally would
have been largely or completely drowned out over winter.

It wasn't, and the first adults came out extremely early. And then
 on April 10 I counted 39 of them in my study site, which is more
 than I had seen at all my sites put together in most of the last
several years! Similarly, the Pygmy Blue, which is normally
eradicated by flooding in the Suisun Marsh every winter, flew
all winter and resumed breeding in March for the second time
in 35 years!

So is the crisis over? Hardly. My "take" on this is as follows:
butterfly populations normally suffer heavy mortality over winter,
probably due to a mixture of drowning, freezing, and bacterial
and fungal diseases favored by mild and wet conditions near
the ground. This droughty winter providentially reduced this
mortality to the point where populations that had declined to
the point of invisibility became visible again. But the underlying
mechanisms of decline, whatever they are, are still in place.
What is happening right now might just be a detour on the
highway to Hell. But the message for butterfly lovers is "Enjoy
it while it's here!"

Paul Cherubini
El Dorado, Calif.


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