Monarch declines, reasons why
I’ve been researching monarch butterflies, alarmed by their almost total absence this summer, but here’s more cheerful news before I relay what I’ve learned: The fall hawkwatch season has begun. Henry Walters is back to staff New Hampshire Audubon’s hawkwatch up at Miller State Park, open daily through Nov. 15.
The views are great, the company is, too, along with the excitement of witnessing hawks sailing by on wind currents or hitching a ride high on thermal lift on warm, sunny days.
The annual big day up at the watch is Sept. 14, timed to coincide with the impressive flights of broad-winged hawks that evacuate New England in mid-September. A rehabilitated hawk will be released back into the wild at 1 p.m., always a thrill that elicits applause from gathered observers.
The Harris Center’s annual big day on Crotched Mountain is the following Saturday, Sept. 21. Crotched Mountain Rehabilitation Center has cleared the views from Blueberry Ridge, site of the watch, and created the very user-friendly Gregg Trail to get you there.
Meade Cadot and I will be providing color commentary for that watch.
Henry Walters is giving a hawkwatch workshop Sept. 12 at the Harris Center in Hancock, 7 p.m. In addition to ID tips, I hope he will read some of his daily narratives of hawkwatch goings-on that he files along with numbers of hawks sighted. Not to be missed.
I heartily recommend working your schedule to allow visits with Henry to help the daily tally. Fall hawk migration is one of nature’s great wonders.
About monarch butterflies: Most years at the hawkwatch, “monarch” is a word heard often as the small figures pass by on their way to high-elevation conifer groves in Mexico. Hawkwatch chat includes wonderment over such a long journey with destination reached in November.
The monarchs that make the trip hatch this time of year and are known as the “supergeneration.” Decreasing daylight triggers hormonal changes that suppress reproduction and thereby lengthen life. Instead of a one-month lifespan typical of other generations, the supergeneration migrates to Mexico, overwinters, and begins the first leg of the return trip north in March and April.
Reproductive biology turned on again, they mate and the females lay eggs on milkweed — usually in Texas. Most of the supergeneration then die, although a few bedraggled ones manage to make it North again. The monarchs we greet in New Hampshire are a couple generations removed from Mexico.
There are many components to monarch survival, but the two most important are the conifer forests in the mountains of central Mexico where monarchs overwinter, and milkweed, the only plant monarchs lay their eggs on because it’s the only food the caterpillars eat.
Both are under siege. Despite establishment of a protected monarch butterfly reserve, the fir forest is being logged illegally as a means of livelihood for an expanding local population. The forest, where intact, provides an insulating blanket that protects monarchs from wind, rain and cold — a lethal combination.
Monarchs by the thousands “festoon” each fir tree in several colonies in the reserve. “Festoon” is the verb used, and appropriately so.
This past winter there was a record low number of colonies, and a record low accumulative area when the colonies were added up: 2.94 acres. Two decades ago, the average winter acreage was 22 acres; in the past decade, the average fell to 12 acres. Last winter’s 2.9 acres was a precipitous dive.
As for milkweed, their host plant, monarch numbers increased historically with the spread of the corn/soybean belt that took over the central states reaching up to the Great Lakes. As prairie grassland was converted to agriculture, the soil disturbance favored milkweed. Far more milkweed colonized corn and soybean fields than the natural prairie or any other landscape.
Gardeners know that milkweed takes advantage of disturbed soils. Up come the little green shoots of common milkweed, Asclepias syriaca, the hearty species most essential to monarch reproduction.
Monarchs arriving in the Midwest encountered a bounty of milkweed, and their numbers skyrocketed as caterpillar survival rates were high.
In 1996, agricultural practices changed with the introduction of soybeans genetically engineered to survive the weed-killer glyphosate, sold as Roundup. “Roundup-ready” corn followed a few years later. Today 90 percent of corn and soy crops are genetically modified organisms, or GMOs, engineered to survive herbicides that kill milkweed as well as other wildflowers that pollinators rely on for nectar.
The more recent push for biofuels, subsidized by the federal government to cut imports of foreign oil, increased demand for corn. When prices spiked, farmers converted more acreage to corn, including millions of acres in the Conservation Reserve Program that paid farmers to manage environmentally sensitive land for natural resource values, not intensive agriculture.
Intensive agriculture also swallowed up the small farms with wild field edges and hedgerows between fields where wildflowers grow.
The decrease in monarch butterflies directly coincides with the increase in Roundup-ready crops in the central states, an area that produces the majority of butterflies, including the generation that heads east to New England. Isotope studies of adult butterflies can ID which region’s milkweed a butterfly fed on as a caterpillar. Most supergeneration monarchs that winter in Mexico originate in the Central U.S. on up to the Great Lakes.
New England’s rich bounty of milkweed produced an abundance of butterflies last year, but other regions did not. Drought and heat waves in the central states took a toll. Monarch eggs don’t survive temperatures above 95 degrees, and drought withers milkweed as well as other nectar plants.
Monarchs live in the Goldilocks zone: Conditions can’t be too hot or too cold; too wet or too dry — both in their winter habitat and summer breeding. Increasing extremes in weather brought on by climate change are providing challenges to monarch survival in addition to extreme loss of milkweed habitat.
Schoolchildren won’t be finding monarch caterpillars to bring into the classroom this fall. I hope attention will be paid to the reasons why. Of course it’s about more than monarchs.
Backyard Birder by Francie Von Mertens appears every other week in the Monadnock Ledger-Transcript.