Seen any butterflies flutter by? Weird weather this year produced enough extra vegetation and flower nectar to support uncommonly large numbers of several butterfly species in Northern California, says UC Davis ecologist Arthur Shapiro. In his daily surveys of butterfly habitats from Donner Pass to Suisun Marsh, Shapiro is finding an abundance of sad duskywing butterflies; fiery, field and eufala skippers; Lorquin's admirals; and the widely recognized monarchs. "This is one of the three biggest years for monarchs in the past 26 years," Shapiro says. "They're at about twice their average numbers." The very dry late winter and spring and cool, relatively wet summer are probably responsible. Noticeably absent are checkered white, pygmy blue and California tortoiseshell butterflies. But Shapiro says low numbers of some species aren't particularly worrisome; his lengthy records show that periodic population peaks and valleys are typical. September and October are the best months for butterfly-watching in Northern California. As days get shorter and nights grow cooler, butterfly activity will decline; autumn's approach is already evident in the westward flights of monarchs heading for coastal winter quarters.