November 23, 2013 at 11:43 pm #1205MikeKeymaster
Where Have All the Butterflies Gone?
By Jane Kay
San Francisco Chronicle
Tuesday 09 May 2006
Last year, surprisingly large numbers of painted ladies migrated
through Northern California – this year, few have shown up.
Wild fluctuations in California’s winter and spring weather have
hurt fragile butterfly populations, causing numbers to fall to the
lowest in more than three decades and increasing the concerns of
scientists about long-term declines linked to climate change and
UC Davis Professor Arthur Shapiro, considered one of the most
prominent butterfly trackers in North America, said Monday he has found
fewer butterflies this year than at anytime since he came to California
35 years ago.
“We have a severe depression of butterfly numbers at the lower
elevations in Northern California, particularly in the Central Valley.
We don’t know if local populations are extinct or have dropped to low
levels that we’re unlikely to detect,” he said.
Shapiro, an entomologist and professor of evolution and ecology,
monitors 10 locations from Suisun Marsh to the Sierra Nevada and
maintains one of the two largest butterfly databases in the world. The
other is the British Butterfly Monitoring Scheme.
At most of the study sites, he has seen half or less than half the
number of species typically present at this time in an average year.
Near Vacaville at Gates Canyon in April 2005, he found 21 species and
378 individual butterflies. But last month he counted 10 species and 43
Many species already appear to be suffering from a serious
long-term decline because of several factors, including changes in
climate and loss of habitat, he said.
“This short-term anomaly has really kicked the populations while
they’re down and may have accelerated their decline,” said Shapiro.
Species hit hard this year include the sooty wing, the large
marble, the mourning cloak, Lorquin’s admiral, the small checkered
skipper, the sandhill skipper, the field skipper, the buckeye, the
eastern tailed blue, the silvery blue and the migratory painted lady.
This is what Shapiro thinks is happening with many species:
The temperature in the state didn’t drop enough to give the
butterflies a certain amount of chilling, the cue to end their winter
dormancy, be it in the form of larvae, pupae, egg or adult. They
remained dormant and died because they couldn’t take advantage of the
food available during the one week of very warm weather in February in
the Bay Area and Central Valley. The few that might have emerged in
March probably died in the cold, wet conditions.
Jessica Hellmann, an assistant professor of entomology at the
University of Notre Dame who researches butterflies throughout North
America, has reviewed Shapiro’s data and said it is critical in
determining long-term changes in butterfly populations.
“We have similar observations for 2006 in California,” Hellman
said. “It is only because Art has 35 years of data that we can say 2006
is bad and is worse than it’s been in a long time.
“Without long-term records, we can’t quantify the growing influence
of humans on biological diversity.”
Hellmann and other scientists have published studies on checkerspot
butterflies, showing, among other findings, that extinctions of two
local populations were hastened by increasing variability in rain, a
phenomenon predicted by global warming models.
Last year, the orange-and-black painted lady stunned Northern
Californians by turning up in a migration of millions, if not billions.
But this year, only a few painted ladies are known to have arrived, and
earlier than normal, according to UC Davis scientists.
Painted ladies typically breed once in the late winter in the
Mojave Desert, then in the Bay Area and the Central Valley and then in
the Pacific Northwest, all in a year’s time as the generations move
This year they appeared to have given up trying to breed in the
southern deserts because of the unusually dry weather that didn’t
produce the plants that the butterflies needed in their caterpillar
stage, scientists believe. They flew to Northern California earlier
than usual and tried to breed with no apparent success, Shapiro said.
He doesn’t know yet whether they reached the Pacific Northwest.
“There doesn’t appear to be any organized migration on the west
side of Sierra,” he said, adding that he has seen only one painted lady
this year in the Sacramento-Davis area and has received reports of only
three others in the area. But he cautioned that just because they’re
not here doesn’t mean there aren’t painted ladies elsewhere. This
particular species typically expands in some areas while contracting in
others, he said.
Six feet of snow still blankets parts of the Sierra, so Shapiro
hasn’t been able to count butterflies on the 7,000-foot Donner Summit
or the 9,000-foot Castle Peak north of Donner Summit. Over the years,
he has found the greatest number of butterfly species – 115 – at Donner
This year’s anomalous late arrival of butterflies goes against the
longer-term trend. Many species this year are running four to six weeks
later than normal instead of the three weeks earlier that his long-term
data show, he said.
Based on his long-term database, the analysis of 23 species over 31
years found that many of the butterflies are coming out earlier in the
spring than in the past. Shapiro and one of his students, Matt
Forister, correlated the earlier appearance with trends in the weather
data in the Sacramento-Davis area.
For those species that had a statistically significant earlier
appearance, the average shift was 24 days earlier. Any shift can
disrupt the butterflies’ survival. There’s a synchronicity in nature,
and many butterflies need to have certain plants available during a
certain time in their life cycle.
Shapiro said that for many years he “pooh-poohed the evidence that
butterfly populations were going downhill. But all that changed in
1999, when a whole bunch of low-elevation species showed an
unmistakable drop-off, and the decline has continued.”
But he remains optimistic that the butterflies will survive.
“Butterflies have been around for 40 or 50 million years,” he said, “so
they’ve been through it before.”
The Painted Lady
Painted ladies breed on desert annuals in Death Valley, then
migrate north to breed again in the Bay Area and Central Valley.
This year, the dry desert produced few plants, and the butterflies
apparently stopped breeding. Only a few have been seen in Northern
Hardest Hit Species of Butterflies
Scientists blame the state’s wild weather in 2006 for the worst
year for butterflies in 35 years. UC Davis scientists are seeing half
or less than half the number of species present at this time in an
average year and far fewer individuals. The mild winter disrupted the
lifecycles of some species, and the resulting change in the food supply
Butterfly Species Hit the Hardest:
Small Checkered Skipper
Eastern Tailed Blue
Migratory Painted Lady
Source: UC Davis.
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