Nature lovers awaiting the monarch butterfly’s reappearance in northern climes have had to be extra watchful this year. High temperatures during the monarch’s fall migration to Mexico—and a drought-induced reduction in the amount of nectar available en route—halved the insects’ winter population, driving it well within the range of potential collapse, experts say. Monarchs spending the winter of 2019-20 in the oyamel fir (Abies religiosa) forests of Central Mexico occupied about 2.8 hectares (seven acres), compared to six hectares (15 acres) the previous winter, according to the World Wildlife Fund. Scientists estimate that when the butterfly (Danaus plexippus) covers at least six hectares—with each hectare accommodating between 10 million and 50 million monarchs clinging to trees—its population is not in immediate danger of collapse. Orley “Chip” Taylor, who directs the nonprofit conservation group Monarch Watch, says sightings of returning monarchs this spring indicate the migration... [Log in to read more]