There is a ray of hope for the vanishing Western monarch butterflies. The number wintering along California’s central coast is bouncing back after the population, whose presence is often a good indicator of ecosystem health, reached an all-time low last year. Experts pin their decline on climate change, habitat destruction and lack of food due to drought. An annual winter count last year recorded fewer than 2,000 butterflies, a massive decline from the tens of thousands tallied in recent years and the millions that clustered in trees from Northern California’s Mendocino County to Baja California, Mexico in the south in the 1980s. Now, their roosting sites are concentrated mostly on California’s central coast. …The Western monarch butterfly population has declined by more than 99% since the 1980s because of the destruction of their milkweed habitat along their migratory route as housing expands into their territory and use of pesticides and herbicides increases.