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The US Endangered Species Act aims to recover threatened species and preserve their ecosystems, often through habitat management and restoration. In the face of climate change and phenological shifts, however, habitat management can seem futile. One of the most conspicuous effects of climate change is that many species are shifting in phenology, i.e., the timing of life history events. These shifts are assumed to have population-level effects on at-risk species, although it is less clear whether these effects are likely to be positive or negative. Here, we use a 27-year-long data set of Fender's blue (Icaricia icarioides fenderi), an endangered butterfly, to investigate long-term changes in abundance and phenology at nine sites near Eugene, Oregon, USA. For Fender's blue, day of peak flight activity consistently advanced at all sites from 1993 to 2019. At the same time, Fender's blue populations increased at some sites and abundance was not changing at others. There was no association of population growth and advancement of peak flight activity. This suggests that although phenological shifts may be a "fingerprint" of climate change, they may not always be a cause for concern. Implications for insect conservation Lessons from Fender's blue butterfly are likely applicable to conservation of other at-risk butterflies. Despite a rapidly changing climate, at least some rare species can be conserved and recovered with appropriate habitat management. [ABSTRACT FROM AUTHOR]