In January of 1992, which is usually the middle of the winter dry season, a weather pattern attributed to "El Nino" created a two week period of cold, wet conditions in the roosting areas, followed by freezes and even snowfall, Lincoln Brower and Bill Calvert estimated mortality to be 70% at several roosts. According to Bill Calvert, mortality at the roost sites is normally 15-20%, so a 70% loss was very alarming. This loss, coupled with usual threats to the integrity of the roosting sites, such as deforestation, once again drew considerable media attention to the problems of Monarch conservation. 4. If there were 20,000 monarch butterflies in this roosting area how many would have been lost (70%)?