Phenological scoring of citizen science observations of five native California milkweed species

Understanding phenological strategies can be complicated by organisms’ use of multiple cues, changing effects of cues over phenophases, and local adaptation. We investigated the importance of spring temperature and rain-year precipitation on phenology in five species of milkweeds (Asclepias spp.) in the western United States, a region with variable temperature and moisture conditions. We categorized participatory science milkweed observations into budding, flowering, and post-flowering phenophases, and matched observations to year- and site-specific climate conditions. We separated climate effects on phenology into variation across sites vs. variation across years to look for evidence of local adaptation in phenology. Warmer mean spring temperatures generally advanced phenology, while wetter rain-years generally delayed phenology. Across all milkweed species × phenophase combinations, spring mean temperature advanced phenology by 2.56 ± 1.71 days spring temp °C -1 (mean ± SD), and preci..., , , # Phenological scoring of citizen science observations of five native California milkweed species

[https://doi.org/10.5061/dryad.v9s4mw734](https://doi.org/10.5061/dryad.v9s4mw734)

## Description of the data and file structure

Description of data file d.all_10082025.csv: These data reflect phenology, climate, and timing data created in connection with iNaturalist observations of milkweed species in the western United States.

iNaturalist data download parameters: We downloaded milkweed (genus Asclepias, iNaturalist taxon ID 47906) observations on Nov. 9th, 2023, for the period spanning Jan. 1st, 2010 – Dec. 31st, 2021. We restricted our search to the western United States by including only observations from the iNaturalist region “Western United States and Canada” (place ID 65360) and then removing any observations from Canada (place ID 6712). We included only verifiable observations, but we included those that did not have enough identifications to reach research grade, because we ...,