Wildlife’s 73% average decline needs the right denominator

Its dataset includes 35,803 monitored populations across 5,790 vertebrate species. The global index’s weighted average decline is 73%. This is a measure of how monitored population sizes changed, not a census finding that 73% of all animals disappeared or a statement that 73% of species went extinct. [1][2]

Two questions give different-looking results. Ask how the weighted index changed, and a baseline of 100 falls to 27. Ask how many monitored populations declined, and the report’s split is 50% declining, 43% increasing and 7% stable. The magnitude of changes and weighting matter, so the second distribution does not invalidate the first result. [1][2]

Nor does the unchanged headline figure from the 2024 report mean that wildlife remained unchanged: the dataset and historical estimates are revised. Geographic and taxonomic coverage also constrain what the index can describe. For a reader assessing conservation claims, ask for the population, time period and metric before accepting a dramatic percentage. The data show substantial decline alongside real increases in some monitored populations; neither justifies treating every ecosystem as identical. [1][2]