Research output

The use of opportunistic data for IUCN Red List assessments

Research output: Contribution to journalA1: Web of Science-article


  • Nick J.B. Isaac
  • Colin A. Harrower
  • Ben Collen
  • Arco J. van Strien
  • David B. Roy

External Organisations

  • CEH - Centre for Ecology and Hydrology
  • University College London
  • Statistics Netherlands


Original languageDutch
JournalBiological Journal of the Linnean Society
Issue number3
Pages (from-to)690-706
Publication statusPublished - 2015


IUCN Red Lists are recognized worldwide as powerful instruments for the conservation of species. Quantitative criteria to standardise approaches for estimating population trends, geographic ranges and population sizes have been developed at global and sub-global levels. Little attention has been given to the data needed to estimate species trends and range sizes for IUCN Red List assessments. Few regions collect monitoring data in a structured way and usually only for a limited number of taxa. Therefore, opportunistic data are increasingly used for estimating trends and geographic range sizes. Trend calculations use a range of proxies: i) monitoring sentinel populations, ii) estimating changes in available habitat or iii) statistical models of change based on opportunistic records. Geographic ranges have been determined using: i) marginal occurrences, ii) habitat distributions, iii) range-wide occurrences, iv) species distribution modelling (including site-occupancy models) and v) process-based modelling. Red List assessments differ strongly among regions (Europe, Britain and Flanders, north Belgium). Across different taxonomic groups, in European Red Lists IUCN criterion B and D resulted in the highest level of threat. In Britain, this was the case for criterion D and criterion A, while in Flanders criterion B and criterion A resulted in the highest threat level. Among taxonomic groups, however, large differences in the use of IUCN criteria were revealed. We give examples from Europe, Britain and Flemish Red List assessments using opportunistic data and give recommendations for a more uniform use of IUCN criteria among regions and among taxonomic groups.

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  • Maes_etal_2015_BiologicalJournalLinneanSociety

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