In 2019, 1,500 volunteers counted seals in 90,000 drone photos of a California island; some counts came within 5% of expert totals

In 2019–2020, over 1,500 citizen scientists analyzed 90,000+ drone images to count wildlife on California's Año Nuevo Island. During winter breeding season, volunteers matched expert seal counts within 5%, but accuracy dropped sharply (to ~46%) when sea lions and seals shared beaches simultaneously, causing species confusion. Researchers found that averaging counts from 11+ volunteers, using medians while discarding low outliers, improved reliability, demonstrating citizen science works well for simple, single-species identification tasks but struggles with species overlap.