Eastern monarch butterfly population doubles in a year

Migratory insects covered 4.2 acres in Mexican forests this winter but number remains far below long-term average

The population of eastern monarch butterflies - who migrate from Canada and the US to Mexico during the winter - has nearly doubled over the last year, according to a recent report commissioned in Mexico, generating optimism among nature preservationists.

The modest growth in numbers for the orange-and-black butterflies follows years of ongoing conservation efforts - and perhaps provides a sliver of optimism after otherwise discouraging long-term trends for the species.