Evaluating effectiveness of captive rearing for endangered Oregon silverspot butterflies

Endangered butterfly conservation efforts often rely on captive breeding and reintroduction programs to sustain populations. Key to understanding the success of these efforts is knowing whether or not captively reared individuals contribute to the population. Without this knowledge conservation efforts may miss the mark. Oregon silverspot butterfly, Speyeria zerene Hippolyta, is an endangered butterfly for which captive rearing and reintroduction efforts have been ongoing for 20+ years with little indication of long-term success. To measure the success of these efforts, in 2021 we conducted a mark recapture study to compare the reproductive contribution of wild and captively reared female butterflies. We marked and released 152 captively reared adult butterflies, 62 of which were female. We also marked every wild butterfly we encountered, a total of 175 adults, 52 of which were female. Captive butterflies emerged, on average, three weeks after wild butterflies. We resighted 24 (45%) of the wild females laying eggs, and only 9 (15%) of the captive reared females laying eggs. This suggests that captive females are not contributing to the population, likely because they are released too late and their late emergence does not allow for female reproductive diapause. These results are key for informing how reintroduction efforts proceed in the future to guarantee they have the most benefit to populations as possible. They also demonstrate the importance of evaluating whether or not conservation strategies are meeting stated goals.