CR 35:59-77 (2007)  -  doi:10.3354/cr00714

Characterizing bird migration phenology using data from standardized monitoring at bird observatories

Endre Knudsen1,*, Andreas Lindén2, Torbjørn Ergon1, Niclas Jonzén3, Jon Olav Vik1, Jonas Knape3, Jan Erik Røer4, Nils Chr. Stenseth1

1Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, 0316 Oslo, Norway
2Department of Biological and Environmental Sciences, Integrative Ecology Unit, PO Box 65 (Viikinkaari 1), Helsinki University 00014, Finland
3Department of Theoretical Ecology, Ecology Building, Lund University, 22362 Lund, Sweden
4Lista Bird Observatory, 4563 Borhaug, Norway

ABSTRACT: Long-term data from standardized monitoring programmes at bird observatories are becoming increasingly available. These data are frequently used for detecting changes in the timing of bird migration that may relate to recent climate change. We present an overview of problematic issues in the analysis of these data, and review approaches to and methods for characterizing bird migration phenology and its change over time. Methods are illustrated and briefly compared using autumn data on garden warbler Sylvia borin from a standardized mist-netting programme at Lista bird observatory, southern Norway. Bird migration phenology is usually characterized rather coarsely using a small number of sample statistics such as mean, median and selected quantiles. We present 2 alternative approaches. Smoothing methods describe the within-season pattern in the data at an arbitrary level of detail, while fitting a parametric seasonal distribution curve offers a coarse description of migration phenology relatively robust to sampling effects. Various methods for analyzing linear trends in the timing of bird migration are reviewed and discussed. Exploratory studies using long-term data gathered at bird observatories can yield more detailed insight into the phenomenon of bird migration and how phenologies relate to climate. Methodological advances are needed, particularly in order to better characterize the shape of phenological distributions and separate between sampling effects and ‘true’ phenology.

KEY WORDS: Bird migration phenology · Climate change · Bird observatories · Monitoring · Day-to-day variability · Seasonal model · Smoothing

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Cite this article as: Knudsen E, Lindén A, Ergon T, Jonzén N and others (2007) Characterizing bird migration phenology using data from standardized monitoring at bird observatories. Clim Res 35:59-77

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