<P> During the migration, the eastern and western populations tend to group together during the migration and then at the overwintering sites . These roosts form along the migration routes, and scientists have used these roost locations to map out the flyways of the entire population . Prior to the discovery of the overwintering sites in Mexico, Fred Urquhart observed roosting behavior in south - migrating butterflies in Mexico and Michoacan . He documented 1500 monarchs roosting at lighthouse point Florida . In California, monarchs have been observed roosting in a wide variety of locations: Fremont, Natural Bridges Beach, golf courses, suburban areas . California roosts differ from those in Mexico . Roosts are observed in inland areas and on non-native tree species . </P> <P> Overwintering sites in California, Northwestern Mexico, Arizona, the Gulf Coast, central Mexico and Florida share the same habitat characteristics: a moderating climatic conditions (thermally stable and frost free), are relatively humid, allow access to drinking water and have the availability of trees on which to roost and avoid predation . California has more than 200 overwintering sites . Overwintering sites have also been observed in coastal South Carolina along with ovipositing females . On the US East Coast, they have overwintered as far north as Lago Mar, Virginia Beach, Virginia . </P> <P> At least twenty colonies exist in Mexico . </P> <P> California overwintering sites exist in areas that are developed and are not considered especially forest - like . These sites have been referred to as having a uniform vegetation population of either Monterey pine or eucalyptus trees and are sometimes present in urban areas . Over wintering sites are dynamic in that tagged butterflies are observed in different roosts throughout the winter . Monarchs overwintering along the Gulf Coast and in Florida do not enter diapause and breed year - round . </P>

Where do monarch butterflies migrate to and from