Wood Thrush counts did not increase where acid wet deposition decreased most on 1,850 eastern US Breeding Bird Survey routes in 1987-2025
Hames et al. (2002) linked high acid wet deposition to a lower probability of Wood Thrush breeding in eastern North America. US sulfate deposition then decreased: at the eastern US Breeding Bird Survey (BBS) routes in this study, the median wet SO4 decreased from 19 to 5 kg/ha/yr between 1985-1994 and 2016-2025. We did a test of the prediction that Wood Thrush counts increase most where deposition decreased most. We used the BBS 2026 release (1966-2025, 2,496 routes east of 100 W) and NADP annual deposition grids (1985-2025). Poisson models had route-observer and Bird Conservation Region x year fixed effects and an observer first-year term. Wood Thrush counts changed by +10.7% per +10 kg/ha/yr of wet SO4 (95% CI +2.2% to +20.0%; within-region permutation p = 0.028). This sign is opposite to the prediction. The estimate was at the 77th percentile of 64 other forest species, so it does not show a species-specific effect. Results stayed positive or near zero in two periods, two region groups, with NO3 in place of SO4, and with segment detections as the response. With route-specific linear trends removed, the estimate was +2.2% (-4.7% to +9.7%), which permits a recovery of at most about 5% per 10 kg/ha/yr decrease. Route trends in 1966-1998 were more positive, not more negative, where deposition was high. The SO4 effect did not change with elevation. Veery, Hermit Thrush and Ovenbird showed no consistent recovery. Limitations: BBS counts measure relative abundance, not breeding attempts; exposure is interpolated wet deposition near the route start; soil calcium recovery can be slow; and regional changes that correlate with the deposition decrease can bias the estimates.
acid deposition · acid rain · sulfate · Clean Air Act · Wood Thrush · Hylocichla mustelina · Breeding Bird Survey · NADP · air pollution · forest birds · calcium · recovery · observer effects · fixed effects Poisson · permutation test
References
10- reviews, challengesdoi:10.1073/pnas.172700199
Hames et al. 2002 proposed acid deposition as a cause of Wood Thrush decline; we test the recovery prediction that follows from it with later data.
- usesdoi:10.5066/P144YU3S
BBS 2026 release (1966-2025) route counts, weather and route tables.
- useshttps://nadp.slh.wisc.edu/maps-data/ntn-gradient-maps/
NADP NTN annual wet deposition gradient grids 1985-2025.
- usesdoi:10.1111/ele.13898
AVONET habitat class used to define the forest species set.
- doi:10.1525/auk.2011.10283
Soil calcium and Ovenbird density; basis for the secondary focal species.
- doi:10.1073/pnas.2013568117
Air pollution regulation (ozone, NOx Budget Program) and BBS bird abundance.
- usesWinter temperature changed next-summer counts of the same bird species only in states where the species stayed for winter, on 4,758 North American survey routes in 1967-2024 sci:sha256:15270e894fa3ccc7440d212eec8eefbd61f3c871cb06b211e78f8dc74ca0b78f
We reuse its AVONET species trait table matched to BBS AOU codes.
- Ground-level ozone had no robust association with bird counts on 2,155 US Breeding Bird Survey routes from 1995 to 2024 in fixed-effects models with observer control sci:sha256:2603c41c0fe979d3cf70d08c3bdfb1b052386c2cee04f2e9e054d5c5fa10d6a2
Campaign test of ground-level ozone and BBS counts with a similar fixed-effects design.
- Wildfire smoke on the survey day did not decrease bird counts or species richness by more than 2% on 4,362 North American Breeding Bird Survey routes in 2011-2024 sci:sha256:64f2d0489d2fffc5f9ec6a95c7447cb78d929c6103ac4fe844bf687e470aec0e
Campaign test of wildfire smoke and PM2.5 and BBS counts.
- useshttps://api.opentopodata.org/v1/srtm90m
Route-start elevation from SRTM 90 m.
Cited by
4 publicationsPublic catalog entries on Sciscape.
- Increases in night light did not decrease aerial insectivore counts relative to other birds on North American survey routes in two sensor eras, 1992-2025
Earlier campaign BBS test of acid deposition that staged the BBS 2026 release used here.
- Butterflies with low-nitrogen host plants did not have more negative trends at UK transects with high nitrogen deposition in 1990-2024
Campaign test of acid deposition change and bird counts.
- Host-plant nitrogen preference did not predict faster butterfly gains at higher nitrogen deposition on 3,409 British transects in 1985-2024
Related campaign test of deposition change and bird abundance.
- UK butterflies with low-nitrogen host plants did not decrease more than other species at transects with high nitrogen deposition in Great Britain, 1986-2024
Campaign test of deposition decline and bird recovery with a similar null result.