The flight of the monarch butterflies

Fri, 09/15/2017 - 11:15am
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The flight of the monarch butterflies

By Kim Gaffett

Monarch butterfly: a stained glass window onto the world.

Its beauty is mesmerizing, but we cannot see through it to comprehend its life forces.

Egg, caterpillar, chrysalis, butterfly; I wish wonder was enough to sustain this life form. 

Around the Island there have been lots of reports of Monarch butterfly sightings; but is it more than usual? Yes! According to Monarch Watch*, 2017 is on track to be the best year for monarchs since 2012 — in all regions of the United States.

Monarch butterflies make truly phenomenal spring and fall migrations. After overwintering in Mexico (or California, or in a small population in Florida), the adult butterfly wakens from its torpor and mates, thus starting the next generation of butterflies to travel north. If weather is good, and food sources available, this next generation will move into the southern United States, breed and send the next generation on its way northward. This pattern of northern movement and creating successive generations continues until the whole U.S. and southern Canada are aflutter with monarch butterflies by late summer. And then, in September at Block Island’s latitude, the last generation of the season will be cued by cooling temperatures, and shortening daylight, to build up fat reserves in their abdomens and migrate to their overwintering site in Mexico. It is nothing short of miraculous that this creature, weighing less than one gram, will fly thousands of miles to the overwintering site of its ancestor, having never been there before. 

Lest we get too excited about this year’s increase in numbers, monarch populations, and the associated phenomenal migration, are still in a declining trend.

A standard measurement tool of the monarch population is the size of the area of forests in Mexico occupied by roosting, overwintering butterflies — clustered together in a form of hibernation. Unfortunately, the size of these areas is trending downward. The overwintering populations in Mexico covered: 18.19 hectares in 1996-97, 6.87 hectares in 2006-07, and, 2.91 hectares in 2016-17. This represents about an 80 percent decrease in overwintering monarch butterflies over the last twenty years.

There are several significant threats challenging the sustainability of monarch butterflies. Destruction of their habitat in the northern summer regions by development of roads, building construction and agricultural expansion is one. Another is the constantly decreasing availability of the host plan, milkweed. Decline of milkweed plants results when they are removed from the landscape by development, or killed by herbicides used by gardeners, landscapers, and farmers. Loss of habitat is also a major problem for overwintering monarchs. One part of the monarch butterfly population overwinters along the southern California coast, thus competing with humans for the same area. However, the majority of the monarch population overwinters in the forests of the Transvolcanic mountains of south-central Mexico. Unfortunately this area is an important logging area for local land owners. The effect of even small amounts of logging can be devastating to monarch populations that are highly concentrated in relatively small areas. (Approximately 100 million butterflies attempt migration each fall, the majority of which concentrate in fourteen (or fewer) roosting sites in Mexico.)

Beyond the facts of a monarch butterfly, is the simple beauty: its egg is like a tiny pearl, its caterpillar an undulous yellow, and green, and black, and white joyous-to-behold pupa; its chrysalis is an organic drop of jade piped with gold, and the butterfly is one of earth’s mightiest stained glass windows.

Enjoy these fluttering beings this fall, who knows what next year’s population will be like. And, be watchful; this may be a year where great aggregations of monarchs on the southeast side of pine trees can be seen in the late afternoon/early evening. They congregate and settle to roost for the night, before fluttering off with the morning’s warming sun to continue their flights southward. 

*Monarch Watch is a non-profit organization based at the University of Kansas. It supports education, research, and conservation for monarch butterflies. Much of the information provided in this column has been gleaned from the Monarch Watch website (monarchwatch.org). Monarch Watch also leads a Monarch tagging program, which the Block Island School second grade has participated in for many years, with the assistance of second grade teachers, Barby Michel, Stacy Henshaw, the Ocean View Foundation, and, now, The Nature Conservancy.

Kim Gaffett is the Ocean View Foundation Naturalist at The Nature Conservancy.