That's a turnaround from last spring, when millions of painted lady butterflies migrated through the Central Valley. But other species have seen steep declines in recent years and could disappear from the region altogether.
"It has been the worst spring for butterflies of my 35 in California," Shapiro said. "There will probably be long-term repercussions, especially for species already in serious decline."
Shapiro said that at most of his study sites, he is seeing half or less than half the number of species present at this time in an average year, and far fewer individual butterflies than usual. For example, at Gates Canyon near Vacaville he counted 10 species and 43 individuals on April 18, 2006. At the same site on April 19, 2005, he counted 21 species and 378 butterflies.
This winter's weather conditions may have a lot to do with the drop in numbers. The early winter was mild, with not enough cold to end the winter dormancy or "diapause" of most butterflies, so they did not emerge to take advantage of early warm weather in February. Then March turned cold and wet, wiping out the breeding of species that had emerged.
While northern California was soaked, the southwest desert has had a very dry "La Nina" winter, leaving little food for the caterpillars of the painted lady. Shapiro said that, as in previous dry winters, the painted lady butterflies had given up on trying to breed in the desert and headed north; a handful were seen in Davis on Feb. 11. Shapiro and his students have seen only one painted lady in the area in recent weeks, when the migration would normally occur.
Apart from this year's weather, several species of California butterflies, including the large marble, sooty wing, Lorquin's admiral an
Contact: Andy Fell
University of California - Davis