Monarch butterflies embark on a marvelous migratory phenomenon. In North America each autumn more than 250 million Monarchs leave the United States and Canada journeying south for up to 2,500 miles to their overwintering roosts in the mountain fir forests of west Mexico City.
Monarch butterflies are known as ‘indicator species’ as they are easy to see and also not afraid of humans. They are considered today’s ‘canaries of the coal mines’. Monarch numbers have been steadily declining – Populations of this once-common iconic black and orange butterfly have plummeted by approximately 90 percent in just the last two decades. The threats to the species are the loss of habitat in the United States–both the lack of availability of milkweed, the only host food plant for monarch caterpillars, as well as nectar plants needed by adults–through land conversion of habitat for agriculture, removal of native plants and the use of pesticides, and loss of habitat in Mexico from illegal logging around the monarchs’ overwintering habitat.
The new population numbers underscore the need to continue conservation measures to reverse this trend. This winter season (2016-2017), there were approximately 2.9 hectares of forest occupied with dense monarchs (somewhere in the neighborhood of 145,000 million overwintering butterflies). This estimate is down some 27% compared to last year.
Monarchs have been tagged in North America since the 1930s. In America the majority of the tags recovered these days are obtained in Mexico. Early each year Monarch Watch personnel visit the overwintering sites, particularly El Rosario and Sierra Chincua, where they buy tags from the guides and Mexican people. The ratio of untagged to tagged Monarchs is quite high and it takes most residents several hours to find each tag among the butterflies, visiting sites along streams or on the trails and under the Monarch-covered trees. The researchers pay 50 pesos (about $7-8) for each tag – reasonable compensation for the time and energy spent locating each tag.
In 2013 BBEMA embarked on the first Monarch tagging and breeding program on Prince Edward Island. Yearly we begin tagging Monarchs on Aug 18th – with a concentrated effort to have all tagged butterflies released by September 20th – a good rule of thumb: when the wild asters, especially goldenrod are in bloom, the monarchs are migrating. With the information from our tagging program we are better prepared to partner with local landowners and scientists to measure changes to our environment and promote conservation initiatives for Monarchs and local pollinators.