Deep snow had larger report contrasts for ground than tree bird pools in eastern feeder samples in 2001-2005 and 2021-2024

We tested whether deep snow had a larger positive link to ground than tree bird reports on the same feeder checklists. We used 125,580 selected North American checklists from 2001-2005 and 2021-2024. Fixed region-specific species pools came from EltonTraits 1.0 and early reporting frequency. Models removed site-winter and state or province by week effects. They controlled reported effort and two-day minimum temperature. Ground-minus-tree contrasts were +0.63 and +1.03 percentage points in the East. Their four-test intervals were +0.02 to +1.24 and +0.54 to +1.51. West contrasts were +0.35 and +0.59; both four-test intervals included zero. Eastern secondary checks kept positive intervals. Deleting any one species kept all four point estimates positive. In later East, the difference included both more ground-pool reports and fewer tree-pool reports. This agrees with a regional food-access prediction but does not identify its cause. Strict trait pools, missing snow reports, selected sites, coarse weather, and group-specific detection limit inference. The study does not measure true occupancy, population gain, pollution effects, or a causal climate-change effect. Source records and transformed record-level data remain external. The package contains code, aggregate evidence, figures, exact source hashes, and independent checks.

feeder birds · snow depth · foraging traits · community composition · observation bias · temperature control · regional replication · Project FeederWatch