Migration
Unlike other butterflies, monarchs cannot survive the cold winters of the Northern climates; so each year, millions of specially adapted butterflies set off on what is known as one of the greatest feats in the animal world. The annual migration of monarchs sees them travel up to 4,800 km along the California-Mexico coast. The monarch butterfly is the only known butterfly species to travel a two-way migration, as birds do, and is the longest annual migration made by any insect (Schmidt-Koenig, 1979).
The migratory generation:
During the summer breeding season, monarch butterflies live for 2 – 5 weeks, during which they mate and lay eggs. The last generation of the year do not become reproductive, instead they remain in a state of ‘reproductive diapause’. This is the generation that migrate south for the winter. The butterflies in this generation can live as long as 9 months (Walton et al. 2005).
Unlike other butterflies, monarchs cannot survive the cold winters of the Northern climates; so each year, millions of specially adapted butterflies set off on what is known as one of the greatest feats in the animal world. The annual migration of monarchs sees them travel up to 4,800 km along the California-Mexico coast. The monarch butterfly is the only known butterfly species to travel a two-way migration, as birds do, and is the longest annual migration made by any insect (Schmidt-Koenig, 1979).
The migratory generation:
During the summer breeding season, monarch butterflies live for 2 – 5 weeks, during which they mate and lay eggs. The last generation of the year do not become reproductive, instead they remain in a state of ‘reproductive diapause’. This is the generation that migrate south for the winter. The butterflies in this generation can live as long as 9 months (Walton et al. 2005).
![Picture](/uploads/2/2/3/1/22319976/9455122.png?540)
Beginning in August, as the temperatures begin to drop and the daylight hours begin to decrease, the migratory generation in southern Canada and eastern North America begin their journey (Figure 1). The western population migrate to numerous overwintering areas along the California coast, with the most famous being the Pacific Grove on the Monterey Peninsula (Resh & Carde, 2009). The eastern population migrate to central Mexico where over 12 overwintering sites have been identified, all of which are above 3,200 m altitude. Scientists have estimated that over 40 million monarchs per hectare can be found in some overwintering sites. Their extraordinary behaviour as they densely aggregate on Monterey pines, cypress and eucalyptus branches is well studied and photographed (Urquhart & Urquhart, 1978).
The butterflies remain huddled together for warmth in dense clusters on tree branches and trunks, periodically flying to water sources (Figure 2). They remain in this hibernation state from mid-October through to March, until the temperatures warm and the daylight hours lengthen. The migratory generation of monarchs then finish development, breed and lay up to 400 eggs before they die (Resh & Carde, 2009). The newly emerged monarchs begin the journey back north, but unlike the generation before them who made a one-generation journey south, it will take three to four generations to reach their northern breeding range (Urquhart & Urquhart, 1978). Two or three summer generations repopulate North America, before a new ‘super generation’ is born the following year.
The butterflies remain huddled together for warmth in dense clusters on tree branches and trunks, periodically flying to water sources (Figure 2). They remain in this hibernation state from mid-October through to March, until the temperatures warm and the daylight hours lengthen. The migratory generation of monarchs then finish development, breed and lay up to 400 eggs before they die (Resh & Carde, 2009). The newly emerged monarchs begin the journey back north, but unlike the generation before them who made a one-generation journey south, it will take three to four generations to reach their northern breeding range (Urquhart & Urquhart, 1978). Two or three summer generations repopulate North America, before a new ‘super generation’ is born the following year.
![Picture](/uploads/2/2/3/1/22319976/9493686.jpg?310)