The Naturalist's Corner: A tale of two monarchs
I was on the Blue Ridge Parkway last weekend scouting for an upcoming Alarka Expeditions trip, “Migration Celebration” which will be on Oct. 4. Monarch butterflies will be one of the migrants we will be celebrating. As I was nosing around at my first stop the other day a couple of monarchs drifted by. I stopped and began to watch — there was a steady stream of monarchs cruising by.
The next overlook I stopped at provided more monarchs and piqued my curiosity. According to reports, last winter’s (2018-2019) population of eastern monarchs on wintering grounds in Mexico was the largest in 12 years, approximately 300 million — up from a low of around 33 million in 2013. And it looks like this population has maintained through the summer breeding period but we won’t know for sure until the monarchs are back on their wintering ground and can be censused again.
This little bug is an amazing migrant. When it starts to make landfall in early spring in Texas, Florida and Louisiana it falls into that “normal” butterfly life cycle, the adult mates and dies, most adults last around a month. Caterpillars hatch and pupate, emerge as adults and continue pushing northward. Monarchs make it as far north as Canada by the end of the summer and that’s when things start to change.
The last generation of summer monarchs is not sexually mature when it leaves the chrysalis and, instead of continuing north, it turns and begins its southward trek back to the Sierra Madre Mountains of Mexico. This trip for some monarchs is more than 2,000 miles. One monarch tagged in New York City’s Central Park on August 25, 2005 was recaptured at the El Rosario Monarch sanctuary on Valentines Day, 2006 — a distance of 2,150 miles. Many of the monarchs I observed last week were at ground level, nectaring a little bit, but continuing to move along. But when I glassed the sky above with my binoculars there would also be monarchs wafting along in a southwesterly direction. They have been found migrating at altitudes above 11,000 feet.
There are two populations of monarchs in North America — eastern and western. The eastern population has always been larger and, as mentioned before, has seen an uptick in numbers. Most of the smaller western population (west of the Rockies) overwinters in Southern California. As has been pointed out in this column before, nature is not as tidy as we often try to make it. Recent studies show that some of the western bugs actually make it to Mexico and that some eastern monarchs have been found overwintering in California. Genetic studies have shown no distinction between eastern and western population and they breed freely wherever they overlap.
But while the eastern population has shown some recent population growth, the western population could be approaching extinction threshold. The 2018-2019 overwintering population of western monarchs was estimated to be around 30,000, representing a 99 percent decrease in population since the 1980s.
If you want to experience a little of this eastern monarch resurgence, join Alarka Expeditions and me on Oct. 4. There will be, of course, numerous species of migrating songbirds as well, plus we’ll make it down to Caesars Head State Park to catch some migrating raptors too. For more information visit www.alarkaexpeditions.com/upcoming-events.