Hubbard Brook 10-ha plot birds (1969–2025) share year-to-year change with plots 8–13 km away but not with BBS routes; regional trends predict 44% of the decrease and none of the recovery

Question: at what spatial scale do bird population changes on the Hubbard Brook Experimental Forest 10-ha plot (New Hampshire; territory mapping, 1969–2025) agree with changes elsewhere? Approach: we compared the plot with three replicate 10-ha plots 8–13 km away (1986–2000), the valley-wide point-count survey (373 points, 1999–2016) and North American Breeding Bird Survey (BBS) routes in six radii from 50 to 450 km (1969–2024). We used Poisson route-observer fixed-effects indices and trends, permutation nulls for year-to-year correlations, and a regional expectation of the plot total (1969–1978 plot abundance multiplied by each species' BBS index). The plan was fixed before the comparisons. Findings (22 species, 200 km): year-to-year log changes on the plot correlated with the replicate plots (mean r = 0.23–0.41, p ≤ 0.013) but not with the BBS at any radius (r = 0.01–0.05). BBS route groups 0–200 km and 200–450 km shared annual change (r = 0.46), and the valley survey shared it with the BBS (r = 0.29). Long-term trends correlated (r = 0.55), but only through four species that decreased 3–5 times faster on the plot than regionally (Least Flycatcher, Wood Thrush, American Redstart, Swainson's Thrush); without them r = 0.08, and sign agreement was 50%. Regional trends predicted a fall of the 27-species total from 182 to 143 birds by 2000–2009; the observed value was 92, so the regional trends predict 44% of the loss. From 2000–2009 to 2015–2024 the plot increased by 26% while the regional expectation decreased by 9%. Against 85 single BBS routes, the plot had lower sign agreement than 81% of the routes and a wider spread of species trends than 91%. Limitations: plot, valley and BBS methods and spatial grains differ; plot counts are small; after 2020 the plot uses fewer trace values, so part of the recent increase in less common species can come from a change in recording practice. We do not test the local causes.

Hubbard Brook · breeding birds · population trends · spatial scale · Breeding Bird Survey · synchrony · territory mapping · long-term monitoring · forest birds · New Hampshire