Samenvatting
Citizen science -- the systematic involvement of volunteer non-professional participants in scientific data collection,
classification, and analysis -- has emerged as a transformative pillar of modern zoological research, providing spatial and
temporal coverage of animal distributions, population trends, and behavioural ecology at scales that professional survey
networks cannot match. This review synthesises evidence from 192 primary studies (2005-2025) examining the
contribution, data quality, participant engagement, and policy relevance of citizen science in European zoological
research. We evaluate eight major European citizen science programmes across five performance dimensions -- data
volume, taxonomic coverage, data quality relative to professional surveys, geographic coverage, and policy linkage --
and conduct a meta-analysis of 44 paired data quality studies comparing citizen science and professional survey outputs.
Mean detection rates in standardised citizen science protocols reach 84.4 +- 6.8% of professional survey reference
values for birds and 78.4 +- 8.4% for butterflies; occupancy models correcting for imperfect detection reduce this gap to
statistically non-significant differences for 76.4% of species. iNaturalist European records (> 80 million occurrences by
2024) have extended documented ranges for 284 invertebrate and plant species and provided first-detection records for
48 invasive species in European countries. Structural barriers -- volunteer retention, spatial sampling bias, taxonomic
identification errors, and data standardisation -- are evaluated alongside solutions including automated image
identification (iNaturalist AI, PlantNet), gamification, and community validation workflows. A framework for integrating
citizen science data into EU Habitats Directive Article 11 surveillance reporting is presented.