Monarch Butterfly Migration

That most regal of butterflies, the monarch, is a common sight this time of year in the southern Appalachians and down through other southeastern states to Texas. They are heading south, to Mexico. Those of us along their migration route may see hundreds gliding silently overhead on any day between mid-September and mid-October.

It is nearly unimaginable that a creature so small, so fragile, should be able to fly to Mexico, but millions do. One monarch was tagged near Toronto, Canada, and was found, some weeks later, at a winter roost in Mexico. How long would it take you, a thousand times larger than a butterfly, to travel that same distance under your own power?

Monarchs accomplish this impressive feat by “fueling up” on the nectar of flowers.  Just a little sugary sap sends them on their way. Once they reach their destinations, they may not eat again until the next spring, and rely on a store of fat to sustain them. While the adults eat nectar from a variety of flowers, the caterpillars only eat milkweed. Milkweed grows naturally throughout much of North America, and planting milkweed is a way to increase Monarch numbers. It is best just to plant the milkweed and wait for Monarchs to show up rather than trying to raise them artificially, as this article from the New York Times explains.

Their wintering locations are unique habitats. Monarchs in the eastern part of North America winter in the mountains of Mexico. There the perfect combination of moist and cool, but not freezing conditions, allows the monarchs to slow their metabolism and survive without eating. They neither dry-out nor freeze. They usually huddle together in huge groups of hundreds of butterflies, and I’ve even seen them cluster together high in the tulip trees of the Southern Appalachian mountains on a cool migration evening.

Monarch numbers in their overwintering grounds have declined dramatically since 1990. The all-time low was in 2013, with both 2012 and 2014 also alarmingly low. The good news is that numbers started to inch back up in 2015 and 2016, but there is real concern that this year, after a slew of hurricanes, the numbers might drop again.

If you get a chance to look closely at a monarch, you can tell whether it is male or female. The sexes are patterned differently from each other, but the differences are subtle. The black veins on the hind wings of male butterflies are thinner than the veins of females. The male also has a black spot in the center of each hind-wing.

One of the best places to observe monarch migration is the Cherry Cove overlook on the Blue Ridge Parkway near mile marker 416.

To stand in the midst of a monarch migration, as they suddenly appear over the trees to the north, glide by within a few feet, then drop off the ridge to the treetops in the south, is an immersion into the natural world.

It’s worth the effort.

Male monarch butterfly. Note spots on thin veins of hindwing. Image may not be used without permission.

Leaf Color Change

Leaves have started to change here in the Southern Appalachians and I've had lots of questions about them, so here is an excerpt from Mountain Nature:

Leaves are green because they contain chlorophyll, which reflects green light while absorbing red and blue. We see the color of light that is reflected, not absorbed, by the leaf. By reflecting green light, however, the plant misses the valuable energy in that particular wavelength. They therefore trap as much as possible with additional, accessory pigments in the leaves, which capture some of the energy that chlorophyll misses and then transfer that energy to chlorophyll.

During spring and summer, the green of chlorophyll masks the colors of the accessory pigments, which include carotenoids and anthocyanin. The carotenoids are a group of closely related, common pigments that are present in most leaves (and carrots). They absorb green and blue light, reflecting orange and yellow. Anthocyanin also absorbs green and blue, but it reflects red. Thus, the carotenoids appear yellow or orange and anthocyanin red or purple.

On a fall day, the hills are alive with these vibrant colors. In the fall, so many leaves become various shades of yellow and red because the chlorophyll in those leaves breaks down, but the accessory pigments remain or are synthesized. As the days shorten, deciduous plants decrease the production of chlorophyll and it quickly disappears from their leaves. Since the accessory pigments are more stable, they persist and delight our eyes. In some cases, plants even produce more accessory pigments, especially anthocyanin. Once the green of chlorophyll is gone, these other colors shine through. 

Beautiful color appears every year at about the same time because the shortening days of fall signal the trees to begin the process of chlorophyll loss, but some years are more colorful than others. Good growing conditions during the summer (warm and wet) ensure that every leaf is packed with pigments and every tree is loaded with leaves, setting the stage for a spectacular show. During the peak period of leaf change, which is usually mid-October for the Southern Appalachians, several converging conditions produce a short, but extremely colorful season. A cold snap intensifies the color because cold temperatures break down chlorophyll quickly, thereby revealing the accessory pigments. Dry weather also intensifies the color because anthocyanin, present in sap, becomes more concentrated as the water in sap evaporates away. Excess water dilutes the sugary sap, as anyone knows who has tasted a watery, wet-weather cantaloupe. Finally, since sunlight also destroys chlorophyll, sunny weather intensifies the color. The best color show, therefore, occurs during a fall season that is dry, sunny, and cool at night. When these conditions are met, a short but spectacular show results, and it is the timing of the cold snap that determines when the show begins.

It is time to get outside and enjoy these brisk and colorful fall days. Enjoy!

Red maple leaves reabsorbing chlorophyll. Image may not be used without permission.