Quasi-extinction risk and population targets for the Eastern, migratory population of monarch butterflies (Danaus plexippus)
Semmens BX, Semmens DJ, Thogmartin WE and others. Scientific reports, March 2016.
Read the paper Free to read · doi:10.1038/srep23265
What this paper is about
The eastern population fell by about 80 percent over a decade. This paper models the risk of it dropping below the point of recovery, and works backwards to a population target.
It provides the numeric goal that monarch conservation planning across the three countries has since been measured against.
Summarised here from the abstract below. Not the authors’ words.
Abstract
The Eastern, migratory population of monarch butterflies (Danaus plexippus), an iconic North American insect, has declined by ~80% over the last decade. The monarch's multi-generational migration between overwintering grounds in central Mexico and the summer breeding grounds in the northern U.S. and southern Canada is celebrated in all three countries and creates shared management responsibilities across North America. Here we present a novel Bayesian multivariate auto-regressive state-space model to assess quasi-extinction risk and aid in the establishment of a target population size for monarch conservation planning. We find that, given a range of plausible quasi-extinction thresholds, the population has a substantial probability of quasi-extinction, from 11-57% over 20 years, although uncertainty in these estimates is large. Exceptionally high population stochasticity, declining numbers, and a small current population size act in concert to drive this risk. An approximately 5-fold increase of the monarch population size (relative to the winter of 2014-15) is necessary to halve the current risk of quasi-extinction across all thresholds considered. Conserving the monarch migration thus requires active management to reverse population declines, and the establishment of an ambitious target population size goal to buffer against future environmentally driven variability.
Abstract reproduced from the published paper, which is licensed CC BY. Copyright remains with the authors.
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Milkweed USA. (2026). Quasi-extinction risk and population targets for the Eastern, migratory population of monarch butterflies (Danaus plexippus) (listing). Retrieved DATE, from https://milkweedusa.com/research/quasi-extinction-risk-and-population-targets-for-the-eastern-2016/
"Quasi-extinction risk and population targets for the Eastern, migratory population of monarch butterflies (Danaus plexippus) (listing)." Milkweed USA, 2026, https://milkweedusa.com/research/quasi-extinction-risk-and-population-targets-for-the-eastern-2016/. Accessed DATE.
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title = {Quasi-extinction risk and population targets for the Eastern, migratory population of monarch butterflies (Danaus plexippus) (listing)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/research/quasi-extinction-risk-and-population-targets-for-the-eastern-2016/},
note = {Accessed DATE}
}