Using mark-release-recapture and distance sampling methods to estimate population size of Oregon silverspot butterflies

The Oregon silverspot butterfly has persisted at low or very low population sizes despite decades of conservation efforts, including reintroduction of captive-reared butterflies at several sites. To date, monitoring efforts have relied on index counts, which do not reliably provide information about population size and have limited use in projecting population trends. There is a need for a comprehensive approach that incorporates detection probability and produces reliable estimates of population size to assess population trends. This information is needed to provide a solid, quantitative foundation for conservation planning. We employed mark-release-recapture (MRR) and distance sampling techniques to estimate the population size of Oregon silverspot butterflies at three sites in Oregon and compared estimates derived from both methods. Our findings will inform the development of a long-term monitoring scheme that can be consistently applied by multiple agencies across various sites, improving efforts to monitor and conserve Oregon silverspot butterfly populations.