In a new study, Monarch Watch Director Chip Taylor and colleagues have shown that speculation regarding the declining monarch population, despite having received much attention, is unsupported.
Published Aug. 7 in the journal Frontiers in Ecology and Evolution, the researchers show that the decline in the monarchs’ overwintering numbers is not due to an increase in the deaths of monarchs during the migration — the “migration mortality hypothesis.” The main determinant of yearly variation in overwintering population size, they found, is the size of the summer population.
Taylor, a University of Kansas professor emeritus of ecology & evolutionary biology, said the monarch butterfly populations have been declining for most of the last two decades. The numbers of monarchs measured at the monarch overwintering sites in Mexico in the winter of 2013–2014 were an all-time low. MORE
Header image: The University of Kansas.