It’s one of nature’s most remarkable phenomena.

Each year, millions of monarch butterflies migrate thousands of miles south from Canada and the United States along a central flyway to Mexico. The monarchs then make a miraculous return flight north once spring arrives, making it the only butterfly species that makes round-trip migrations.

But eastern monarch butterfly populations are steeply declining. A catastrophic 80 percent population decrease has occurred over the past two decades.

One cause of the species’ decline may be a loss of monarch habitat, which consists of flowering nectar sources and milkweed. Milkweed is essential for monarch breeding and reproduction. Female monarchs lay their eggs on milkweed leaves, and the plant serves as the only food source for newly-hatched caterpillars.

Monarch habitat has been destroyed by both urban development and changing agricultural practices. In agricultural fields, milkweed is killed by pesticides, and the widespread adoption of genetically engineered herbicide-resistant crops. Activists are warning that these downward trends could lead to the monarch becoming endangered in the next 20 years.

But now scientists are exploring whether city-dwellers might be able to help ensure the species’ survival by replacing some of that lost habitat.

The Keller Science Action Center at Chicago’s Field Museum has teamed up with the United States Fish and Wildlife Service and the Landscape Conservation Cooperatives on a 4-city project dubbed “A Monarch’s View of the City.” The project partners with local organizations in Chicago, Minneapolis-St. Paul, Kansas City, and Austin to monitor urban monarch conservation efforts in each area.

As part of the project, geospatial maps were created from land-use and land-cover data for all four cities. The maps illustrate where milkweed is growing and the potential locations where milkweed can be planted in urban areas between the United States and Mexico.

The Field Museum and its partners are enlisting the help of home gardeners to add monarch habitat in Chicago.

In Chicago’s South Shore neighborhood, Faith in Place Chicago outreach director Veronica Kyle is growing a patch of common milkweed in front of her home. Clutching the underside of a milkweed leaf, Kyle excitedly locates a monarch egg.

“Milkweed is like a welcome sign for monarchs,” Kyle said. “It’s a symbol of survival.”

At Saint Benedict the African East parish in the city’s East Englewood neighborhood, Field Museum social scientist Adriana Fernandez arrives with milkweed seeds to be planted outside the church.

Encouraging residents to plant milkweed is a key component of the “A Monarch’s View of the City” project that could help prevent monarch butterflies from becoming an endangered species.

“If we could get 5 percent, 10 percent of all residents to go out and do some plantings, it would make a huge impact,” the Field Museum’s Keller Science Action Center geographic information manager Mark Johnston said.