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Changes in phenology and abundance of an at-risk butterfly


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.

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Data Availability

All data and code for analyses available in Online Resources 1, 2, and 3.


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We thank The Nature Conservancy (TNC) at Willow Creek, US Bureau of Land Management at Fir Butte (BLM), and US Army Corps of Engineers at Fern Ridge Reservoir (ACE) for management of sites and permission to survey butterflies. Many have surveyed Fender’s blue butterfly at these sites including Rhiannon Thomas Cochrane, Greg Fitzpatrick, Gary Pearson, Paul Severns, and others. US Fish and Wildlife Service funds annual surveys of Fender’s blue butterflies; DoD Strategic Environmental Research and Development Program (SERDP, award # RC-2700) provided funds for this analysis. We thank the Schultz Lab at Washington State University Vancouver and two anonymous reviewers for feedback on previous drafts of this manuscript.


This study was funded by US Fish and Wildlife Service and DoD Strategic Environmental Research and Development Program (SERDP, Award # RC-2700).

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Authors and Affiliations



REB: Conceptualization, methodology, data curation, formal analysis, visualization, writing—original draft preparation. EEC: Funding acquisition, supervision, conceptualization, methodology, writing—review and editing. CBE: Conceptualization, methodology, data curation, software, writing—review and editing. CBS: Funding acquisition, supervision, conceptualization, resources (survey data), writing—review and editing.

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Correspondence to Rachael E. Bonoan.

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Bonoan, R.E., Crone, E.E., Edwards, C.B. et al. Changes in phenology and abundance of an at-risk butterfly. J Insect Conserv 25, 499–510 (2021).

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  • Boisduval’s blue
  • Intraspecific variation
  • Lepidoptera
  • Lycaenidae
  • Phenology
  • Population viability