Numerous studies have documented climate-induced phenological changes in a diversity of taxa. An implied concern in these studies is that phenological changes are negatively impacting threatened and endangered species. However, in some cases, advances in phenology are positively associated with population trends, e.g., for multivoltine Leipdoptera in the UK. Few studies assess the association of phenological changes with changes population size and fewer in the context of at-risk species. We evaluate trends in phenology and trends in abundance for at-risk butterfly species across the United States. Data include 24 species that had been identified as of conservation concern by US state or federal agencies at sites with at least 10 years of population monitoring in the states which consider the species at-risk. We estimated trends in abundance and phenology by fitting gaussian curves to regular count data, using generalized linear mixed models. We test the hypothesis that species with greater risks (i.e. faster population decline) are associated with greater phenological changes.
Results/Conclusions
We evaluated phenological changes and population trends in the following species: Acadian hairstreak (SGCN, Illinois), Appalachian Brown (SGCN, Illinois), Baltimore checkerspot (SGCN, Illinois), Black Dash (S3, Illinois), Broad-winged skipper (S1, Illinois), Dion skipper (S3, Illinois), El Segundo blue (Endangered), Eyed Brown (S1S3, Illinois), Falcate orangetip (SGCN, Ohio), Fender’s blue (Endangered), Frosted Elfin (SGCN, Wisconsin), Hermes Copper (Candidate, California), Karner Blue (Endangered), Langes Metalmark (Endangered), Leonard’s skipper (SGCN, Ohio), Long dash (SGCN, Ohio), Mardon skipper (S1, Washington), Mission Blue (Endangered), Oregon silverspot (Threatened), Palos Verdes blue (Endangered), Regal Fritillary (S1, Illinois), St. Francis Satyr (Endangered), Taylor’s checkerspot (Endangered), Wild Indigo Duskywing (S1, New Hampshire). Most of these species are obligately univoltine, a lower proportion than the overall butterfly fauna. We find that phenological change such as date of year is broadly advancing for at-risk butterflies but that trends vary by site and region. Populations tended to be declining, as one would expect with at-risk taxa, with some notable exceptions (e.g., Fender’s blue). We compare the association between trends in abundance and trends in phenology to that reported from past community-wide studies of Lepidoptera.