Wave of Butterflies Slows to a Trickle
By Associated Press (Associated Press) - May 13, 2006
FRESNO – The number of butterflies migrating through California has
fallen to nearly a 40-year low as populations already hurt by habitat
loss and climate change encountered a cold, wet spring, researchers
“Some of them were already in decline, but this weather really added
insult to injury, kicking them when they were down,” said Arthur
Shapiro, a UC Davis entomologist.
Shapiro, who over 35 years of tracking the insects has developed one
of the world’s largest butterfly databases, monitors 10 observation
stations from the Bay Area to the eastern slopes of the Sierra Nevada.
About half of the usual species haven’t shown up, while others – such
as the drab-colored sooty wing or the iridescent eastern tailed-blue
- are fluttering in at one-fourth or less of their usual numbers, he
The change was particularly dramatic for the red and black painted
ladies, which last year enjoyed a possibly record-breaking migration
after feeding on vegetation nurtured by abundant rain in Southern
Last spring, millions of them migrated through the state and into
Oregon, passing Shapiro’s Sacramento site at a rate of four per
second. This spring, he had reports of four painted ladies a month in
the same area.
Erratic weather was part of the problem. A mild winter, warm February
and wet March upset the usual cues that tell butterflies when to
emerge from dormancy, Shapiro said.
As difficult as the soggy March was for butterflies, it may be only
one of many factors contributing to their steady decline, researchers
Long-term changes in rain patterns linked to global warming and the
paving over of habitat could be playing a role, said Jessica
Hellmann, an entomologist with the University of Notre Dame who has
examined Shapiro’s data.
“If you whack a population and whack it again and again, it’ll go
extinct in that area,” Hellmann said.