Extreme uncertainty and unquantifiable bias do not inform population sizes

ROBINSON, ORIN J.; SOCOLAR, JACOB B.; STUBER, ERICA F.; AUER, TOM; BERRYMAN, ALEX J.; BOERSCH-SUPAN, PHILIPP H.; BRIGHTSMITH, DONALD J.; BURBIDGE, ALLAN H.; BUTCHART, STUART H.M.; DAVIS, COURTNEY L.; DOKTER, ADRIAAN M.; DI GIACOMO, ADRIAN S.; FARNSWORTH, ANDREW; FINK, DANIEL; HOCHACHKA, WESLEY M.; HOWELL, PAIGE E.; LA SORTE, FRANK A.; LEES, ALEXANDER C.; MARSDEN, STUART; MARTIN, ROBERT; MARTIN, ROWAN O.; MASELLO, JUAN F.; MILLER, ELIOT T.; MOODLEY, YOSHAN; MUSGROVE, ANDY; NOBLE, DAVID G.; OJEDA, VALERIA; QUILLFELDT, PETRA; ROYLE, J. ANDREW; RUIZ-GUTIERREZ, VIVIANA; TELLA, JOSÉ L.; YORIO, PABLO; YOUNGFLESH, CASEY; JOHNSTON, ALISON

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

NATL ACAD SCIENCES

Lugar: Washington DC, USA; Año: 2022 vol. 119

0027-8424

Species-specific population estimates are fundamental for many aspects of ecology, evolution, and conservation, yet they are lacking for most species. Aiming to fill this gap, Callaghan et al. (1) estimated global bird population sizes by modeling the relationship between eBird reporting rates and independent estimates and extrapolating globally. While we applaud their intention, we caution that their modeling framework is prone to yield extremely uncertain and biased estimates that cannot support robust inferences about species abundance distributions or other applications in ecology, evolution, or conservation (1, 2). Their methods yield extremely large posterior uncertainties for total global bird abundance (3.9 billion to 2,080 billion; figure 2 of ref. 1), and 96% of individual species had posterior uncertainty spanning three or more orders of magnitude. Glaucous Gull (Larus hyperboreus) was listed as the fifthcommonest bird globally; it is difficult to be confident in this conclusion given that the 95% credible interval (CI) for Glaucous Gull overlapped the CIs for ∼67% of all bird species. This uncertainty in species ordering makes it impossible to use these estimates for reliable conservation prioritization as suggested (1). The tremendous uncertainty associated with the estimates of population size results from the inadequacy of the 10 measures used to account for imperfect detection of birds in eBird data (1), for which there is extreme inter- and intraspecific variation in the observation process across regions, time, and habitat (3). eBird reporting rates also depend heavily on species’ overlap with the activity of eBird users, which also varies by region, time, and habitat.