Monarch butterflies fly at the El Rosario butterfly sanctuary on a mountain in the Mexican state of Michoacan in this Nov 27, 2013 file photo. [Photo/Agencies]

SEATTLE - The US Fish and Wildlife Service and conservation groups launched a $3.2 million campaign on Monday to save the habitat of the embattled orange-and-black spotted monarch butterfly, whose numbers have plummeted in recent years.

The monarchs, renowned for migrating thousands of miles (km) over many generations from Mexico, across the United States to Canada, and then back again, have seen a loss in their habitat because of farming and urban sprawl.

The population of monarch butterflies, which peaked in the late 1990s at roughly 1 billion specimens, has fallen by 90 percent in recent years, according to the Center for Biological Diversity.

"Known for its beautiful orange color, fascinating life cycle and remarkable annual migration, the monarch butterfly is the most iconic butterfly in North America," Democratic US Senator Amy Klobuchar, who backs the effort, said in a statement.

The campaign led by the Fish and Wildlife Service, the National Wildlife Federation and the National Fish and Wildlife Foundation includes a conservation fund dedicated to habitat restoration that will involve planting native milkweed and nectar plants, which the butterfly depends on for food and breeding.