A review of the literature and anecdotes showing the "folly" of calculating wildlife decline based on the "natural" populations 40-50 years ago. The history is far longer.
Rowan, Andrew N.
"Shifting Baselines: Understanding the True Extent of Wildlife Decline,"
WellBeing News: Vol. 2
, Article 3.
Available at: https://www.wellbeingintlstudiesrepository.org/wbn/vol2/iss5/3