There’s also an element of uncertainty about what the monarch numbers collected by surveyors really mean. “The year-to-year fluctuation in monarch numbers makes it difficult to put an exact number on the degree to which monarch populations have declined,” says Karen Oberhauser, a conservation biologist at the University of Wisconsin, Madison, who has studied monarchs since 1985. Data from as far back as the 1950s show “it is very clear that monarch butterflies are a very high fluctuation species in terms of their population dynamics,” Agrawal agrees. Populations that crash can recover. Females lay hundreds of eggs, only two of which need to survive for the population to survive. And because four generations occur per year, even if most of the butterflies in Mexico die one year, “there is opportunity for the population to recover.”
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