Ryan James Schmidt , Charles Davis , Lena Struwe, Kristen Elizabeth Saban 

Natural history collections (NHCs) are essential for studying biodiversity. While spatial, temporal, and taxonomic biases in NHCs affect analyses, the influence of collector practices on biases remains largely unexplored. We utilized one million digitized specimens collected in the northeastern United States from 237 herbaria and analyzed contributions from ~10,000 collectors. We investigated (a) similarities and differences between more- and less-prolific collectors, and (b) how these practices influence spatial, temporal, and taxonomic biases. We identified six common collector practices, or collection norms: collectors generally collected (a) different species, (b) from multiple locations, (c) from sites sampled by others, (d) during the principal growing season, (e) species identifiable outside peak collecting months, and (f) species from species-poor families and genera. Some norms changed over decades, with different taxa favored during different periods. Collection norms have increased taxonomic coverage in NHCs, however, collectors typically avoided large, taxonomically-complex groups, causing their underrepresentation in NHCs. Less-prolific collectors greatly enhanced coverage by collecting during more months and from less-sampled locations. We assert that overall collection biases are shaped by shared predictable collection norms rather than random practices of individual collectors. Predictable biases offer an opportunity to more effectively address biases in future biodiversity models.