Sunday, October 21, 2018

Nature: Monarch butterfly numbers increasing by droves

A monarch taps nectar from a swamp milkweed/Jim McCormac

October 21, 2018

NATURE
Jim McCormac

On Sept. 15, 2013, my Nature column covered monarch butterflies. The message was gloomy. Following is an excerpt:

“Far fewer Monarchs are making this journey (to Mexican wintering grounds). Only 20 years ago, their ranks blanketed 45 acres of Mexican fir forest. Last winter, the butterflies occupied less than three acres. Many people have commented on their absence this fall. Some authorities estimate that Monarch numbers declined by 60 percent over the past two years.”

Then, monarchs appeared to be in dire straits, and a prime factor in the butterfly’s decline was the loss of milkweed. Monarchs require these plants as hosts — milkweeds are the only flora that the caterpillars can consume.

There are 13 native milkweed species in Ohio, and monarchs probably use them all. But the two species that do most of the heavy lifting are common milkweed and swamp milkweed. The latter grows in damp soil, and as we’ve lost about 90 percent of our state’s presettlement wetlands, the milkweed has also declined.

The aptly named common milkweed is by far our most numerous monarch fuel, and it will grow in nearly any dry, open habitat. Roadside mowing, excessive herbicide use, and the proliferation of increasingly sterile agricultural landscapes has greatly decreased this plant.

Fortunately, highly nomadic monarchs are quick to capitalize on new opportunities and will readily find new places to reproduce. People heeded a call to action. No one wanted to see the iconic orange-and-black butterflies fall to the wayside, and thus began a fevered campaign of milkweed planting.

The insects have responded. Even postage-stamp-size urban yards are cranking out monarchs, and an army of human foster parents now raise and release the butterflies. Scores of conservation organizations, park districts, highway departments and others have also joined the effort for milkweed production.

On Sept. 30, some friends and I were having lunch on a balcony overlooking a gorgeous wooded valley in southern Ohio. During our hourlong respite, we estimated that 70 to 80 monarchs coursed by on an unerring southwest trajectory. I’ve probably seen more monarchs this fall than in the past five years combined.

Many people have reported similar spikes this year. Late September brought reports of several massive roosts — congregations of thousands of butterflies — along the Lake Erie shoreline. These tough monarchs were resting after an arduous flight across the lake, en route from Canada.

The most accurate assessment of monarch populations comes from evaluating the coverage of butterflies in the Mexican oyamel fir forests where they winter. There, monarchs form shimmering burnt-orange cloaks over the trees, and scientists can calculate the acreage that they occupy.

Last winter, about 6 acres of fir forest were butterfly-filled, a doubling from 2013 when I previously covered this subject. Because of this year’s bumper crop, prospects look even brighter. Chip Taylor of the butterfly-conservation organization Monarch Watch estimates that butterflies could occupy up to 12 acres of fir forest this winter. The butterflies blanketed 45 acres two decades ago, so we’re still a ways from peak numbers.

The upward trajectory of monarch populations is a clear example of how people can positively intervene to help an imperiled natural resource. Congratulations to everyone who has assisted in the proliferation of North America’s most fabled butterfly.

Naturalist Jim McCormac writes a column for The Dispatch on the first, third and fifth Sundays of the month. He also writes about nature at www.jimmccormac.blogspot.com.

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