Butterflies in California – 05/04/2006

  • November 23, 2013 at 11:43 pm #1205


    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
    habitat loss.

    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
    individual butterflies.

    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
    affected others.

    Butterfly Species Hit the Hardest:
    Sooty Wing
    Large Marble
    Mourning Cloak
    Lorquin’s Admiral
    Small Checkered Skipper
    Sandhill Skipper
    Field Skipper
    Eastern Tailed Blue
    Silvery Blue
    Migratory Painted Lady

    Source: UC Davis.

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