To the Editor:

Even if March finally brings relief from winter’s chill, this spring is sending a shiver down my spine. March is when the monarch butterflies take wing from their small forest enclave in the mountains of Mexico. Their numbers have been dwindling. Since the first count in the 1990s, the overwintering population of monarchs, clustered together on dense evergreen trees, has shrunk from a high of 50 acres down to a mere 1.5 acres of the forest this winter. As the monarchs begin their annual flight north, they have the reproductive capacity to rebound, but they face ever tougher odds.

The monarchs’ fate is literally up in the air. There’s the herbicide that again will be sprayed on more than 150 million acres of Monsanto’s “Roundup Ready” corn in the midwest. Back when tillage was used for weed control, farm fields doubled as pretty good habitat for monarchs. Now, the intense spraying of herbicide-tolerant corn and soybeans has largely exterminated the milkweed the monarch caterpillars cannot survive without.

Also airborne are ever greater numbers of carbon dioxide molecules, drivers of the global weirding that buffets wildlife with increasing extremes of drought, heat, and cold. And there’s the political hot air that spawned an irrational subsidy of ethanol production, which since 2007 has motivated farmers to plow up prairie and roadsides to grow more corn and thereby reduce monarch habitat even more. Since the ethanol produced barely equals the energy required to grow the crops, any societal benefit is dwarfed by the vast loss of habitat in the country’s heartland.

Precious few monarchs visited Princeton last year. MonarchWatch.org details the conditions that could allow them to rebound to some extent. But the worry is that, like the passenger pigeons that disappeared early in the previous century, monarchs may need a critical mass to sustain their miraculous migration. Other than supporting national efforts to restore habitat, and reducing our fossil fuel consumption from gulps down to sips, we can seek to be optimal hosts to whatever monarchs reach our backyards. If you have some sunlit areas, DR Greenway and the farmers market are sources for native milkweed species. In my role as a local naturalist, I collected seeds of local genotypes of milkweed last year and plan to grow and share as many as I can. In a world so focused on extraction and consumption, it will take years of effort, advocacy and luck just to keep what we’ve always taken for granted, and to warm up again the feeling of spring.

Stephen Hiltner

North Harrison Street