The World Wildlife Fund says the number of Monarch butterflies that reached wintering grounds in Mexico has rebounded 69 percent from last year's lowest-on-record levels.

Last year, the Monarchs covered only 1.65 acres (0.67 hectares), the smallest area since record-keeping began in 1993.

This year, the butterflies rebounded, to cover 2.79 acres (1.13 hectares), according to a formal census by Mexican environmental authorities and scientists released Tuesday.

Omar Vidal, head of the World Wildlife Fund in Mexico, said while the census is good news, "1.13 hectares is very, very low."

The orange-and-black butterflies are suffering from loss of milkweed habitat in the United States, illegal logging in Mexico and climate change. Each year, the butterflies migrate to Mexico to find the same pine and fir forests to spend the winter.