Citizen science monitoring demonstrates dramatic declines of monarch butterflies in western North America

Count-based PVA allows researchers to assess patterns of population change through time and to evaluate future persistence. We combined state-space models and citizen science data to evaluate viability of the western population of monarch butterflies over 36years. A key feature of our analysis was combining irregular sampling from multiple sites to obtain a single estimate of total abundance using state-space models. The average population growth rate was negative, u=−0.0762 (λ=0.927), average abundance in the 2000s was <5% of average abundance in the 1980s, and current quasi-extinction risk is 72% within 20years. Despite wide confidence intervals in some parameter estimates, western monarch monitoring data provide unambiguous evidence for dramatic population declines. To obtain viable populations, managers could target historic abundance and high enough growth rates to avoid near-term extinction.