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Increasing winter temperatures explain declines in body size of boreal birds
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  • Laura Bosco,
  • Andreas Otterbeck,
  • Andreas Lindén,
  • Thord Fransson,
  • Markus Piha,
  • Aleksi Lehikoinen
Laura Bosco
Finnish Museum of Natural History

Corresponding Author:laura.bosco@helsinki.fi

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Andreas Otterbeck
Finnish Museum of Natural History
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Andreas Lindén
Natural Resources Institute Finland
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Thord Fransson
Swedish Museum of Natural History
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Markus Piha
Natural Resources Institute Finland
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Aleksi Lehikoinen
University of Helsinki
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Abstract

Body size of individuals is typically increasing towards colder and higher latitudes, as larger body size is known to be a thermoregulatory adaptation to colder circumstances. Here we explored the spatio--temporal changes in wing length and body weight of 24 wintering bird species in Northern Europe and how these relate to annual changes in winter temperature. We show that across all species, body size has decreased since the 1970s, with a negative relationship between wing length and temperature anomalies of previous winters, suggesting carry over effects likely linked with body size--related survival or dispersal. Body weight was negatively related with the temperature anomaly of the same winter, indicating more immediate effects related to reduced fat reserves during mild winters. Our results highlight climate--driven decrease in body size across several species and its' association with annual variation in winter temperature in the high latitudes.