May ponds explain the 1974–2026 prairie share of all breeding ducks in the USFWS survey; pintail and wigeon moved north, and prairie mallards were 30% below the pond relation in 2024–2026

Question: in the USFWS Waterfowl Breeding Population and Habitat Survey (traditional area, 1955–2026), did breeding ducks move north beyond what May pond counts predict, and do duck numbers still follow ponds? Data: public stratum estimates and May ponds, uncorrected air counts for 2000–2026, stratum polygons, and April–May air temperature. Method: we fitted the prairie–parkland (PP) share of each species on log ponds (this year and last year) in 1974–1999 and tested 2000–2026 out of sample, with an AR(1) and block-bootstrap null. We also fitted pond-adjusted trends of the share and of the abundance-weighted latitude for 1974–2026 (HAC errors), regional duck–pond models, seven variants, a sampling-error check and a visibility-correction check with uncorrected counts. Results: for all ducks, the 2000–2026 PP share was 64.8% against 62.8% predicted (logit residual +0.09, 95% interval −0.04 to +0.26). The pond-adjusted share trend was +0.010 ± 0.020 logit per decade and the latitude trend −9 ± 8 km per decade. Northern pintail and American wigeon moved north (share −0.20 and −0.23 logit per decade, about 6.5 SE; latitude +55 and +79 km per decade), because fewer birds settled in Canadian prairie–parkland at a given pond count. In 2000–2019, PP ducks were 25% above the 1974–1999 duck–pond relation. With reported estimates this surplus ended in 2023–2026. In the US strata, the ratio of reported estimates to uncorrected counts in 2023–2026 was 0.68 of its 2000–2019 mean (Canada 0.95). In uncorrected counts, US prairie ducks stayed on the 2000–2019 pond relation (log residual +0.02), but prairie mallards were 30% below it (log −0.36; lower than all 17 placebo windows) and were also below it in Canada alone (−0.35). Conclusion: May ponds explain the long-term distribution of all ducks in this survey area. Pintail and wigeon shifted north. The recent end of the prairie surplus of all ducks depends on the lower US visibility corrections, but the recent prairie mallard decrease relative to ponds does not. Limitations: fixed survey area; pond visibility cannot be checked; the 2023–2026 tests have 3–4 years and were added after we saw the data; uncorrected counts assume constant visibility; no causes were tested.

waterfowl · breeding distribution · range shift · Waterfowl Breeding Population and Habitat Survey · prairie pothole region · May ponds · drought displacement · visibility correction · mallard · northern pintail · American wigeon · out-of-sample test · aerial survey