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Forest type explained about half of the gap between spatial and temporal bird community temperature slopes on 2,523 forested US routes (1966-2025), but not in open-habitat birds, the East, or species

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5 citing publications

Question: bird community temperature indices (CTI) of the North American Breeding Bird Survey follow in time only a small part of their spatial temperature slope. Does vegetation, which sorts by climate but changes over centuries, mediate the spatial slope, so that only its vegetation-independent part can appear in decades? Data: BBS 2026 release (1966-2025; 107,922 runs, 466 species, contiguous US), nClimGrid temperature and precipitation, USFS/FIA 250 m forest type maps (28 groups, 133 types). Method: a vegetation thermal index (VTI) per route from the US-wide temperature of each forest type, cross-fitted by 4 degree block; route-mean CTI on temperature with and without VTI and forest share; temporal slopes on route warming trends with route or route x observer fixed effects; 500 joint block-bootstrap resamples; a plan written before the outcomes. Results: on 2,523 forested routes, VTI correlated with temperature at 0.92, and at fixed temperature the CTI increased by 0.21 C per C of VTI (95% CI 0.13-0.28). The total spatial slope was 0.42 (0.40-0.44) C per C; the direct slope was 0.24 (0.18-0.29) with groups and 0.20 (0.14-0.28) with types. Temporal slopes were 0.028 (0.005-0.056) and 0.080 (0.050-0.116). Vegetation removed 47-64% of the gap (pre-registered threshold met only with types). For 157 low-pitched species without observer hearing drift, temporal tracking was 39-63% of the direct slope and vegetation removed 66-82% of the gap. Mediation was strong for forest birds (direct/total 0.40) and absent for open-habitat birds (0.85). It was weak inside the East (0.82; none beyond precipitation and winter temperature), where tracking stayed at 3-21% of the direct slope, and the regional prediction failed. For 394 species, neither the total (-0.18) nor the direct slope (-0.05) predicted the response to differential warming. Conclusion: slow forests explain about half of the continental bird tracking deficit, but not the eastern, local, open-habitat or species-level deficits. Limitations: one vegetation snapshot (about 2004); VTI also carries other climate information; non-forest vegetation not mapped; correlational design.

community temperature index · climate tracking · climate debt · vegetation lag · forest type · space-for-time substitution · Breeding Bird Survey · Forest Inventory and Analysis · nClimGrid · thermal niche · mediation · observer effects · birds · United States
Populations and Evolution

References

18
  1. uses, supportsUS breeding bird communities sort by temperature almost as strongly between nearby routes as across the continent, but in time they follow only 3-24% of this slope (BBS 1966-2025)
  2. uses, supportsLong-serving Breeding Bird Survey observers recorded fewer high-pitched birds; because cold-adapted species sing higher, this drift made 31-77% of the within-observer CTI warming trend (1966-2025)
  3. supportsCommunity thermal composition in 75 monitoring networks followed about 12% of its own spatial temperature gradient in time; a lag fit gives fast adjustment to a small target (1948-2025)
  4. supportsYear-to-year temperature responses of 320 North American bird species followed 5-14% of own spatial gradients, with no clear lasting part; 49 British butterfly species followed about 50% in 2 summers
  5. usesRemeasured US forest plots showed small mortality-driven tree community warming of 0.014-0.018 C per decade in West and East, 2001-2025; species permutation did not separate it from turnover
  6. supportsBird community temperature index followed less than 10% of May-July warming on 5,294 North American survey routes in 1970-2024 with route and observer controls
  7. Bird species centroids moved about 35 km north on 1,471 fixed North American survey routes from 1975-1989 to 2010-2024, at about 14% of the isotherm shift and not in proportion to it
  8. Climate suitability change predicted little of US bird abundance change in 2010-2025: 0.05 per log unit within species on survey routes, and no species-level forecast skill
  9. Finnish atlas range margins of southern birds moved north more slowly in 2006-10 to 2022-25 than before while isotherms moved fast; lower detection in 2022-25 explains part of this
  10. Demersal species redistribution offset 24% of bottom temperature change in 11 North American trawl series in 1970-2020, but the offset came from the Northeast US fall survey
  11. Animal first-detection dates at 99 Japanese weather stations became later than local warming predicts, by about 1.1 days per decade more than plant dates, in 1953-2020
  12. Australian temperate reef fish thermal index followed 3-year SST at 0.35 C per C in 2008-2020 and again in 2021-2026, but only through region-wide year changes (549 sites)
  13. useshttps://www.sciencebase.gov/catalog/item/6a0b0b0ab66b0188da36aedd
  14. useshttps://data.fs.usda.gov/geodata/rastergateway/forest_type/
  15. usesdoi:10.1175/JAMC-D-13-0248.1
  16. usesdoi:10.1111/ele.13898
  17. usesdoi:10.1098/rspb.2024.1908
  18. useshttps://stacks.stanford.edu/file/vy474dv5024/bbsrtsl020.fgb

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