The 2015-16 monarch butterfly population estimates were released today by our partners in Mexico. Numbers reflect a 255% increase in the area occupied by monarchs in the overwintering habitat since last year. Overwintering monarch butterflies occupied approximately 10 acres of habitat in Mexico this year compared to last year’s estimate of 2.8 acres. This is great news but more work is needed to restore the eastern population of monarchs.
After a phenomenal two month long migration from the United States and southern Canada, the North American monarch butterfly reaches Mexico, where it spends the winter months. There, monarchs cluster together in small areas of habitat, and each winter the population is estimated by the total area they occupy in the overwintering grounds.
Long story short, monarchs are still struggling but as we work with Mexico and Canada, we are making a difference to restore their habitat. In recent years, monarchs have decreased by 90% since peak populations in the mid-90s. Loss of milkweed and prairie habitat in the United States, along with loss of habitat in the overwintering grounds have contributed to the decline of this incredible insect.
Mexico established the Monarch Butterfly Biosphere Reserve in 1980 to protect the monarch’s mountainous home. Just over 60 miles from Mexico City, the 138,000 acre reserve is sectioned off into several sanctuaries that provide winter refuge to the millions of monarchs who migrate to Mexico each fall. From roughly late October through February, monarchs live in the forested mountains of Mexico, where temperatures are mild enough for survival. This habitat is only found on 12 mountaintops on the planet, and is essential to the persistence of the monarch and its migration.
The monarchs cluster in Mexico’s rare oyamel fir forests, occasionally taking shelter in pines and other trees. The oyamel trees provide much needed refuge and protect the butterflies from extreme temperatures, rain, snow and predators.
While in Mexico, monarchs go through four stages: arrival, the establishment of overwintering colonies, colony movement and finally, spring dispersal. After arrival, monarchs will fly around during the day and seek out the best location for colony establishment. As temperatures drop, monarch movement decreases, and the butterflies form large, dense clusters on oyamel branches, coloring the forest orange.
By mid-December, monarchs have settled into their overwintering homes. The butterflies roost on tree trunks and tree branches. In fact, monarchs cluster in such great numbers that the oyamel fir branches give way to the weight and begin to bend. Overwintering population counts are completed at this time, as it’s the coldest time of the year, and the monarchs are gathered together, in several predictable areas, with little movement.
Since the winter of 2004-05, the World Wildlife Fund and the Mexican National Commission of Protected Natural Areas have measured the number of monarch butterflies at the overwintering grounds. To provide some context, in the winter of 2013-14, experts reported the lowest monarch population on record with an occupied 1.66 acres of overwintering habitat. In 1996-97, monarch populations peaked with estimates reporting more than one billion monarchs occupying 44.5 acres of habitat.
The final stage usually begins in mid-February as temperatures rise. Monarchs will disperse from their overwintering habitat, and descend down the mountains in search of water and warmer temperatures before they begin their spring migration in March.
How can you help monarchs as they prepare to migrate North this spring? Plant native milkweed and native wildflowers, avoid tropical milkweed and delay mowing during times of peak monarch activity in your area. Everyone and every little bit of habitat can help. The more monarchs we have, the better they can withstand extreme weather and climate events.
Learn more about monarch conservation: http://www.fws.gov/midwest/monarch/
Learn more about how monarch populations are estimated: http://www.learner.org/jnorth/monarch/spring2016/05/monarch-butterfly-population-size.html#slideshow