For the purposes of this study, we defined long-term species monitoring as the repeated, systematic collection of data with the intention to detect changes over time in the abundance or distribution of 1 or more predefined taxa or taxonomic groups. The bias of monitoring data toward certain vertebrate taxa, particularly charismatic species, and toward developed countries reflects a similar bias across biodiversity information more generally (Amano et al., 2016; Beck et al., 2014; McRae et al., 2017; Scheele et al., 2019; Troudet et al., 2017). The 41 countries selected for the search included the 7 countries targeted for in-country searches by partners, as described above, to obtain a measure of detectability, all 17 megadiverse countries (Mittermeier et al., 1997), all of the world's 10 largest countries, and a number of randomly selected countries in regions underrepresented by other methods (Appendix S2). Keywords: biodiversity surveillance; citizen science; megadiverse countries; population trends; taxonomic bias; ciencia ciudadana; países megadiversos; sesgo taxonómico; tendencias poblacionales; vigilancia de la biodiversidad; ; ; ; ; EN biodiversity surveillance citizen science megadiverse countries population trends taxonomic bias ciencia ciudadana países megadiversos sesgo taxonómico tendencias poblacionales vigilancia de la biodiversidad 1 14 14 03/02/22 20220201 NES 220201 INTRODUCTION Data on long-term trends in species abundance and distribution underpin efforts to track and understand the global biodiversity crisis, to target scarce conservation resources to priority species and sites, and to quantify the impact of those investments (Borges et al., 2018; Butchart et al., 2010; Díaz et al., 2019). [Extracted from the article]