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<p>Migratory birds that arrive early to their breeding sites occupy higher quality habitat, secure preferred mates, and may gain fitness advantages. It is widely assumed that arrival date is subject to natural selection, and thus localities where montane breeding birds arrive earliest may be most optimal, representing a tradeoff between abiotic limitations (e.g., climate) at higher elevations, and biotic factors (e.g., predators, food, nesting sites) at lower elevations. We used autonomous recording units to determine apparent territory establishment date (hereafter ‘established territory’) of Swainson’s Thrush (<i>Catharus ustulatus</i>) across an elevational gradient within the White Mountains, New Hampshire. Thrushes apparently established territories at high elevations (1200&#xa0;m) 6.6&#xa0;days earlier than at lower elevations (250&#xa0;m). Additionally, we explored the role of mean growing season temperature, aspect, and annual variability (year) to territory establishment. Annual variability was the only covariate that demonstrated statistical support where territory established in thrushes was about two days earlier in 2020 versus 2019 and 2021. We suspect this delay may be explained by variation elsewhere in the annual cycle, as we did not observe differences in general climatic conditions (snow depth, precipitation, temperature). We found support suggesting Swainson’s Thrush establishes breeding territory earlier at high elevations perhaps due to the strong association between spruce-fir forests and high elevation, which is likely due to preference for this vegetation type. Montane ecosystems are at risk when considering the changing climate, and warming temperatures may threaten the vegetation that sensitive breeding birds rely on.</p>

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Phenology of Swainson’s Thrush apparent territory establishment across an elevational gradient

  • 期刊论文

  • 发表日期：

    2026年6月26日

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  • Sarah C. Deckel,
  • William V. DeLuca,
  • Lauren M. Chronister,
  • Alexander R. Gerson,
  • David I. King

摘要

Migratory birds that arrive early to their breeding sites occupy higher quality habitat, secure preferred mates, and may gain fitness advantages. It is widely assumed that arrival date is subject to natural selection, and thus localities where montane breeding birds arrive earliest may be most optimal, representing a tradeoff between abiotic limitations (e.g., climate) at higher elevations, and biotic factors (e.g., predators, food, nesting sites) at lower elevations. We used autonomous recording units to determine apparent territory establishment date (hereafter ‘established territory’) of Swainson’s Thrush (Catharus ustulatus) across an elevational gradient within the White Mountains, New Hampshire. Thrushes apparently established territories at high elevations (1200 m) 6.6 days earlier than at lower elevations (250 m). Additionally, we explored the role of mean growing season temperature, aspect, and annual variability (year) to territory establishment. Annual variability was the only covariate that demonstrated statistical support where territory established in thrushes was about two days earlier in 2020 versus 2019 and 2021. We suspect this delay may be explained by variation elsewhere in the annual cycle, as we did not observe differences in general climatic conditions (snow depth, precipitation, temperature). We found support suggesting Swainson’s Thrush establishes breeding territory earlier at high elevations perhaps due to the strong association between spruce-fir forests and high elevation, which is likely due to preference for this vegetation type. Montane ecosystems are at risk when considering the changing climate, and warming temperatures may threaten the vegetation that sensitive breeding birds rely on.