Monday was a public holiday in Victoria in honour of the Queen. I’ve often been intrigued by how many birthdays the Queen has in a year, given the numerous dates on which it is celebrated throughout the commonwealth. But it turns out that we were really celebrating the (approximate) birthday of King George III, with the first Monarch’s Birthday celebration held in Australia in 1788. So it seems appropriate to celebrate with a monarch butterfly (Danaus plexippus).
The monarch butterfly is a pretty amazing beast. Native to North America, they migrate from Mexico to southern Canada and back every year, a journey which can take up to four generations. They are following seasonal changes in the abundance of their main food source, milkweed. Typically, it takes three generations to get from Mexico to Canada, with the adults in each generation living for about two months. The fourth “super” generation can live for up to seven months and is capable of making the entire return journey back to Mexico. That’s about 4,000 km – not a bad effort for an insect with a wingspan of ~ 10 cm! Monarchs overwinter in a small area of forest in the Mexican mountains at the Mariposa Monarca Biosphere Reserve, with up to one billion individuals occupying sites that cover less than five hectares within the reserve.
Not much was known about the monarch migration until Fred and Nora Urquhart began researching the monarch butterfly in 1937, recruiting an army of citizen scientists across North America to help them in their quest to find the wintering sites. Individual butterflies were marked with small stickers on their wings and released to continue their journey. Sightings of tagged butterflies were recorded and plotted on a map but it took 38 years before the mysteries of the monarch migration and the location of the wintering sites in Mexico were revealed.
The video below has a nice summary of both the migration and the citizen science movement (and fun things you can do with google earth).
Monarchs are also found in New Zealand (where this photo was taken), Australia and the UK. However, they don’t make the same large-scale migrations (partly because they would totally run out of land, at least in NZ and the UK!).