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Monarchs among the fields...

Monarchs among the fields: Text

“There are idle spots on every farm and every highway is bordered by an idle strip as long as it is; keep cow, plow, and mower out of these idle spots and the full native flora, plus dozens of interesting stowaways from foreign parts, could be part of the normal environment of every citizen.”

Aldo Leopold, a sand county almanac

Image by Daniel Cooke
Monarchs among the fields: Quote

If you pay attention when you drive across the county in any direction, you’ll notice what ecologist Aldo Leopold noticed back in 1949—although the landscape has been dramatically changed from its pre-developed state, there are spaces on the margins of daily life where native plants and the wildlife that depend on them thrive.

Many researchers believe that roadsides are one of the essential habitat sectors for monarch recovery and other pollinators. Monarch caterpillars depend on milkweed, a hardy native plant that flourishes in disturbed habitat such as roadsides. With its thousands of miles of rights-of-way, transportation departments across the six counties have everything they need to create monarch havens and pollinator habitats just a few steps beyond the shoulder line.

It is common knowledge that the North American monarch population is declining. From a high in 1996 to their record low in 2013, the eastern monarch population size fell by over 90%. These population size estimates allow us to assess the status of the population, and set goals for restoring it to a sustainable level. Monarchs’ declining numbers have gained a lot of attention, but how is the monarch population measured anyway?

Each fall, monarchs emerging east of the Rocky Mountains begin an epic journey of up to 2500 miles to forested mountains in central Mexico to survive the winter together. After they have arrived at their overwintering sites in Mexico, and are clustered in oyamel fir trees, the population size is measured. There are too many monarchs to count individually, so the area of forest the monarchs occupy is used as a substitute for the size of their population. This is why monarch population targets are often in units of hectares (1 hectare is about 2.5 acres) instead of number of butterflies.

Monarch scientists have determined that bringing the eastern monarch population size up to 6 hectares of overwintering monarchs by 2020, and sustaining it, would significantly reduce its risk of extinction. Without this increase, the eastern north American monarch has a more than 20% chance of reaching numbers so low that recovery would be unlikely. So, it is critical that we work together to restore enough habitat to bring the monarchs back to at least 6 hectares.

To estimate how much milkweed (as part of diverse habitat that also includes native nectar plants) we need to plant to meet this ambitious goal, we need an accurate estimate of how many butterflies are in a hectare of occupied overwintering habitat. There have been several different approaches to measuring overwintering monarch density. A new study by the monarch conservation science partnership combined the six most widely used measures of monarch density into one more comprehensive estimate. Their work suggests there are about 21.1 million butterflies per hectare.  

Monarchs among the fields: Text
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