It takes two: the value of integrating citizen science and scientific collections in biodiversity research

• Citizen science and collections offer complementary strengths and distinct biases. • Citizen science adds broad coverage and recent data, key for biodiversity research. • Collections provide historical depth and taxonomic precision via voucher specimens. • Both datasets are biased toward accessible areas; remote regions remain under-sampled. • Combining completeness and recency helps identify areas to update and monitor biodiversity. Digitally accessible records are a vital source of primary biodiversity data, with citizen science now surpassing scientific collections in global repositories. Despite known biases in both sources, more work is needed to explore how citizen science can complement scientific collections. We compared these data sources to assess biases and evaluate the contribution of citizen science to scientific collections. Using Mexican bird data from GBIF, we compiled 17,018,068 georeferenced occurrence records, classified as either citizen science or scientific collections. We homogenized taxonomy and cleaned occurrence records using geographic filters and species range maps. Spatial bias was assessed using null models of accessibility. We then evaluated taxonomic patterns, temporal gaps, and survey completeness across multiple spatial resolutions using species accumulation curves and the age of the most recent records. Finally, we identified priority areas where citizen science can help strengthen and update scientific collections. Our results reveal complementary taxonomic and geographic patterns across datasets. Citizen science offers broader spatial coverage and more recent records, whereas scientific collections provide historical depth and taxonomic reliability through voucher specimens. Together, these strengths highlight the value of integrating both data sources to build more comprehensive biodiversity datasets and better inform conservation in a rapidly changing world.