This summer we had the opportunity to study the monarch butterfly and its larval host plant Showy Milkweed in the South Okanagan and Similkameen valleys. Monarchs regularly show up in our area but have not been common since the early 1990s.
Monarchs cannot survive the cold winter temperatures in Canada, and all but a few southern parts of the United States. In North America east of the Rocky Mountains monarchs from as far north as southern Canada overwinter in high volcanic mountains southwest of Mexico City. Conventional wisdom held that our Western monarchs spent the winter at sites along the California coast. But in fact we can’t be sure if our monarchs this fall will end up in Mexico or California.
Whatever their destination, this is a formidable undertaking for a small creature that must deal with controlling its energy supply by nectaring to supplement the fat body which is its in-flight fuel tank, adjust its abdominal weight with water ballast to maintain a centre of mass optimal for gliding and soaring, find thermals and updrafts, compensate for detours and crosswinds, and find hospitable rest stops along the way and all without the Internet, Google maps, or a GPS.
We captured a female monarch in Cawston on Aug. 5 and Eva constructed a cage and filled it with Showy Milkweed, the only plant that monarch caterpillars will consume. Three days later Eva had 83 eggs and after weeks of labour and love by Sept. 25 she had released 53 beautiful monarch butterflies tagged with labels supplied by professor David James from Washington State University.
This is the first release of tagged monarchs from wild B.C. stock to be released and if they make to wherever their destination is and are seen it will be a significant contribution to our understanding of where our monarchs survive the winter months. Our thanks to the B.C. Ministry of Environment, and the B.C. Conservation Foundation for providing funding for this work.
The South Okanagan Naturalist Club meets on the fourth Thursday of the month at 7 p.m. in the basement of the Penticton United Church on the corner of Main and Eckhardt. Visitors are welcome.
Dennis St. John and Eva Antonijevic are biologists and members of the South Okanagan Naturalist Club.