Pacific Northwest birds have shifted their abundances upslope in response to 30 years of warming temperatures
Mountain species are expected to move upslope as temperatures warm, yet their responses vary. Analyzing 30 years of breeding‑bird data from southwestern British Columbia, researchers tested three hypotheses: escalator‑to‑extinction, upslope‑lean and persist‑in‑place. Species’ optimum elevations rose by an average of 126 m, closely tracking warming isotherms, while elevational limits remained stable—supporting the upslope‑lean hypothesis. Many species showed neutral or favorable responses, maintaining stable abundances at lower elevations. However, Canada Jays declined, showing vulnerability to warming. Results highlight the value of long‑term abundance data for assessing climate‑change impacts on mountain species.
Subject Tags
- Forest
- Climate impacts
- Wildlife
Abstract
Mountain species are predicted to respond to warming temperatures by moving to higher elevations that remain relatively cool. Species can track warming by shifting their entire distributions upwards (the “escalator to extinction” hypothesis) or by increasing in abundance in the upper portion of their elevational range while maintaining stable elevational limits (the “upslope lean” hypothesis). Alternatively, mountain species may not change their abundance or distribution despite climate change (the “persist-in-place” hypothesis). Here we evaluate these three contrasting hypotheses by analyzing responses of breeding forest bird species to three decades of warming in southwestern British Columbia, Canada. Consistent with the upslope lean hypothesis, species' optimum elevations (elevations of highest abundance) increased by an average of 126 m, approximately tracking upslope movements in temperature isotherms. In contrast, species' elevational range limits were stable on average, contra the escalator to extinction hypothesis. Many individual species had stable distributions and abundances, and species with upslope abundance increases typically maintained stable abundances within the lower elevation portions of their range. Taken together, most species in our study region appear to be responding neutrally or favorably to warming temperatures. Nevertheless, one mountain species, the Canada Jay, Canada's national bird, is declining and vulnerable to the escalator to extinction within our study region. Overall, we emphasize the importance of empirical data—and abundance data in particular—when evaluating mountain species' vulnerability to climate change.
Citation
Freeman, B. G., Eyster, H. N., Heavyside, J. M., Yip, D. A., Mather, M. H., & Waterhouse, F. L. (2025). Pacific Northwest birds have shifted their abundances upslope in response to 30 years of warming temperatures. Ecology, 106(9), e70193. https://doi.org/10.1002/ecy.70193
TNC Authors
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Benjamin G. Freeman
The Nature Conservancy -
Harold N. Eyster
Climate and Land Use Analyst, Colorado
The Nature Conservancy
Email: harold.eyster@tnc.org