Fourteen duck taxa in the 1961–2026 May waterfowl survey did not follow the northward shift of spring isotherms after pond control; pintail and wigeon moved north and bufflehead moved south

Question: did breeding ducks in the USFWS/CWS Waterfowl Breeding Population and Habitat Survey (traditional area, 50 core strata, 1961–2026, 64 survey years) move north at the rate of April–May isotherms when May pond counts are held constant? Method: for 14 taxa, we calculated the abundance-weighted mean latitude of the strata for each year. We fitted mean latitude on log Canadian prairie ponds and on year, with 5-year moving-block bootstrap intervals. We used the published visibility-corrected estimates and, as a second version, the estimates divided by their visibility correction factors (VCFs). The benchmark is the isotherm shift from GHCN-CAMS April–May temperature at the survey segments (0.24° latitude per decade; 0.20 when weighted by the abundance of each taxon). Results: the mean trend of the 14 taxa was +0.073° per decade (95% CI −0.006 to 0.156; about 8 km per decade). With the VCF removed, it was −0.063 (−0.131 to 0.032). In all 11 bootstrap sensitivity analyses, the upper limit was at or below 0.24. The taxa moved in opposite directions. Pintail (+0.58° per decade, 0.34 to 0.80) and wigeon (+0.69, 0.48 to 1.03) moved north faster than their isotherm benchmarks. This occurred because their prairie numbers fell by 20% and 13% per decade, while their northern numbers did not fall. Bufflehead (−0.29), gadwall and blue-winged teal moved south. All taxa were further south in wet years, but northern spring temperature had little effect. Prairie VCFs fell, mostly from the 1960s to the 1980s, while most northern VCFs are fixed. This difference changes the mean trend by 0.13° per decade, but the main conclusion is true for both versions. The species results agree with two parallel SCI analyses of 1974–2026 (sci:sha256:e29a61d7fc4a9132ff75f1e758fe199642c0a072ccc87ef873c2aef6a8f160b0, sci:sha256:f91cc2a847513b2fcec50d60f32d5ccee59611fa7634473d2b14d9aa43141cc0). Limitations: fixed survey area; stratum-level latitude; crew changes are not modelled; the data are provisional.

waterfowl · breeding distribution · range shift · climate tracking · isotherm velocity · Waterfowl Breeding Population and Habitat Survey · prairie pothole region · May ponds · visibility correction · northern pintail · American wigeon · bufflehead · aerial survey