• (Photo: docentjoyce/Wikimedia Commons)

North American monarch butterflies could face quasi-extinction in the next 20 years, a study has found.

The study, published in Scientific Reports, said there was “a substantial probability” that the monarch butterfly population faced an 11 to 57 per cent chance of quasi-extinction, adding the caveat that “uncertainty in its estimates was large.”

John Pleasants, an assistant professor of ecology, evolution and organismal biology at Iowa State University who took part in the study, told the university that quasi-extinction means that so few individual monarchs would exist that their migratory patterns would collapse and the population likely wouldn’t recover.

The study used historic trends and weather population to develop models that could forecast the future monarch population. The researchers simulated different scenarios and variations to calculate the probability of extinction.

The monarch population in the insect’s overwintering habitat in Mexico had declined 84 per cent between 1996 and 2014, before more than tripling during the winter of 2015-16.

Researchers found that although the increase in population seemed positive, it was as a result of favourable summer weather rather than recent conservation efforts. The researchers warned that although recent findings were not good, additional plantings of milkweed, upon which the monarch lays eggs and feeds caterpillars, could help the population.

Pleasants told the university that planting milkweed in yards and gardens would be a good starting point, but that systematic plating of milkweed along roadsides and conservation lands would help even more.