Populations of monarch butterflies are declining due to logging, changes in climate and the disappearance of the milkweed plant essential to their survival, according to conservation organizations, which reported this spring that monarch numbers in the Mexican forests where they hibernate over winter had been at its lowest in two decades.

"In real estate it's location, location, location and for monarchs and other wildlife it's habitat, habitat, habitat," said Chip Taylor, Director of Monarch Watch, a Kansas-based group dedicated to monarch conservation.

"We have a lot of habitat in this country but we are losing it at a rapid pace. Development is consuming 6,000 acres a day, a loss of 2.2 million acres per year. Further, the overuse of herbicides along roadsides and elsewhere is turning diverse areas that support monarchs, pollinators, and other wildlife into grass-filled landscapes that support few species," Taylor said, adding that replacing diverse cropland with fields of genetically modified corn and soybeans is posing a further threat to populations.

Marianna T. Wright, executive director of the National Butterfly Center in Texas, told USA Today that the 20-year low in monarch populations is not a reason for panic and that the species in not in threat of extinction. But conservation efforts are needed, Wright continued, in order to ensure healthy populations of monarchs will continue.

"It should certainly get some attention," she said. "I do think the disappearance of milkweed nationwide needs to be addressed. If you want to have monarchs, you have to have milkweed."

In urban and suburban areas, milkweed tends to get removed from the landscape in favor of more appealing plants. But the plant is essential to monarch butterfly survival; it is the only plant adult monarchs will lay eggs on, and their caterpillars feed off the plant.

"Many people know milkweed, and many people like it," Travis Brady, the education director at the Greenburgh Nature Center in N.Y., told USA Today. "And a lot of people actively try to destroy it. The health of the monarch population is solely dependent on the milkweed plant."

Chip Taylor of Monarch Watch told the Boston Globe that what's happening to the monarch habitats is "symbolic of what's happening on a larger scale."

He told the Globe that monarchs are part of a complicated ecosystem and a ripple in their world will effect all the birds, flowers and other insects around them.

"We have to keep the connections going, and monarch butterflies tell us we're not doing a good job of that," he said.