The year 1999 was the worst in nearly three decades for butterfly populations in the Sacramento Valley and nearby foothills, said UC Davis ecologist Arthur Shapiro. Weather was probably partly to blame, with a freeze during Christmas week 1998 (which would have reduced the survival of overwintering eggs, caterpillars, pupae and adults), and a cool spring and summer, Shapiro said. "Still, I'm frankly flabbergasted at this year. I expected a lot of species would get off to a slow start but would catch up, but it just didn't happen." He said there was no indication that human activities were to blame. Periodic low numbers of some butterfly species aren't particularly worrisome; his 28 years of records show that population peaks and valleys are typical. And in the Sierra Nevada above 5,000 feet, butterfly numbers were normal or even better than average. In his biweekly surveys of butterfly habitats in the valley, Shapiro found very few or no individuals of 14 of the region's 55 resident species. Some of those most affected are among the most common in the region, such as orange sulphur butterflies, which commonly feed on alfalfa plants and collect on automobile radiators; fiery and field skippers, the little golden butterflies often seen feeding on lantana and marigold flowers; pygmy blue butterflies, which usually appear in alkaline marshes by the thousands; and the buckeye, normally one of the most common butterflies of gardens and urban vacant lots. Also missing: the popular black-and-orange monarch butterflies. "I've been getting a lot of calls about this because schoolteachers who usually raise them in classrooms couldn't find any larvae on wild milkweed plants. Neither could I." At one California coastal grove where the valley's monarchs overwinter, the butterflies are down from an average of 60,000 to about 14,000. In recent days, as a result of the valley's very dry and sunny December, orange sulphur butterflies have started to emerge again in alfalfa fields -- a phenomenon typically seen only in drought years, Shapiro said.