Why there may be much fewer monarch butterfly sightings in the US this summer

Monarch butterfly sightings may be sparser than usual in the U.S. and Canada following a drastic spike in populations wintering in Mexico, researchers told ABC News.

Monarch butterfly sightings may be sparser than usual in the U.S. and Canada following a drastic drop in populations wintering in Mexico, researchers told ABC News.

The annual census of the number of monarchs that winter in Central Mexico showed that the population decreased "precipitously," the Xerces Society for Invertebrate Conservation, which conducts the research alongside the World Wildlife Fund-Mexico, announced on Wednesday.

The number of monarchs dropped from 2.2 hectares in the 2022-2023 season to 0.9 hectares in the 2023-2024 season -- making this past winter the second-worst year ever recorded, according to the environmental nonprofit.

Each hectare is measured to contain about 21 million butterflies, Chip Taylor who is an emeritus professor of ecology and evolutionary biology at the University of Kansas and the founder and former director of conservation nonprofit Monarch Watch, told ABC News.

Monarch populations have declined drastically over the past 40 years, Anurag Agrawal, an evolutionary ecologist and professor of environmental studies at Cornell University, told ABC News.