CR 50:43-50 (2011)  -  DOI: https://doi.org/10.3354/cr01034

Higher degree-days at the time of breeding predict size of second clutches in the barn swallow

Roberto Ambrosini1,*, Nicola Saino2, Diego Rubolini2, Anders Pape Møller3

1Dipartimento di Biotecnologie e Bioscienze, Università degli Studi di Milano-Bicocca, piazza della Scienza 2, 20126 Milan, Italy
2Dipartimento di Biologia, Università degli Studi di Milano, via Celoria 26, 20133 Milan, Italy
3Laboratoire d’Ecologie, Systématique et Evolution, CNRS UMR 8079, Université Paris-Sud, Bâtiment 362, 91405 Orsay Cedex, France

ABSTRACT: Failure to adjust timing of biological events to ongoing rapid climate change may incur negative fitness consequences for organisms and may have severe negative consequences for population viability. We studied long-term trends in breeding phenology and reproductive success of a barn swallow Hirundo rustica population during 1971−2009 in relation to spring accumulated temperature (degree-days). Degree-days at the time of a phenological event constitute a more accurate and meaningful measure of the biological environment than mean temperatures over fixed time intervals, because accumulated temperature determines seasonal development, emergence and reproduction of many organisms, including the invertebrates on which species at higher trophic levels feed. Although laying dates showed an inverted U-shaped trend over time, degree-days at laying of first and second clutches increased linearly, suggesting that barn swallows are becoming increasingly ecologically mismatched relative to spring events. In addition, higher degree-days at laying were associated with smaller second clutches. These findings suggest that barn swallows are currently delaying reproduction relative to spring phenology, with negative consequences for their reproductive output. This delay may thus contribute to the population decline observed over the last decades. Degree-days at the time of reproduction may therefore provide a mechanistic link between phenology, breeding success and demographic trends of migratory bird populations.


KEY WORDS: Degree-days · Ecological mismatch · Fecundity · Hirundo rustica · Phenology · ­Thermal delay


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Cite this article as: Ambrosini R, Saino N, Rubolini D, Møller AP (2011) Higher degree-days at the time of breeding predict size of second clutches in the barn swallow. Clim Res 50:43-50. https://doi.org/10.3354/cr01034

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