The population of monarch butterflies are decreasing in California. This has affected the monarch butterfly grove in Pismo. It’s probably sad to see as the years go by less butterflies are seen here in California. Many people express this feeling especially when going to Pismo specifically to see the butterflies. Monarch butterflies population has decreased by 30% since last year. Whats the cause of this?butterflies face a reduction of breeding habitat in the US due to herbicide application and land use changes as well as forest degradationin wintering sites in Mexico. Extreme weather conditions in all these ecosystems can further their decline.