Studying the timing of bird migration: new staff-student paper published

Anne Goodenough writes about a new scientific publication that sprang from close collaboration between students and staff – a feature of our research in Biosciences Quantifying the robustness of first arrival dates as a measure of avian migratory phenology. Anne E. Goodenough, Stacey M. Fairhurst, Julia B. Morrison, Martin Cade, Peter J. Morgan & Matt J. Wood. 2014. IBIS. DOI: 10.1111/ibi.12227 http://onlinelibrary.wiley.com/doi/10.1111/ibi.12227/full

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Back in the summer of 2012, two third year students, Julia Morrison and Stace Fairhurst, worked with Anne Goodenough and Matt Wood on a research project on the timing of bird migration. This was based at Portland Bird Observatory in Dorset, where Matt is the Scientific Advisor. This involved a two-week placement at the Obs, in glorious sunny weather, staying in an old lighthouse, and with panoramic views of Olympic sailing events that were taking place in Weymouth harbour. Who says fieldwork is dull?! Anyway, back to the science…

In studies of bird migration using first arrival dates goes back to Gilbert White’s work in the late 1700s and is now widely used in studies of current climate change. Portland Bird Observatory, Dorset, UK, has been undertaking a daily bird censuses (number of individuals per species per day) since it became an active observatory in 1961. Because survey effort is fairly consistent and recording is done every day, this gave us a rare opportunity to calculate mean arrival dates and compare them to first arrival dates and find out how “good” first arrival dates are as a measure of migration timing. We found that number of species that showed change over time was approximately equal regardless of whether first dates or mean dates were used, but there were mismatches. Four species showed an advance for mean dates only (Common Tern, Sedge Warbler, Garden Warbler, Reed Bunting). Change in these species would not have been detected if only first arrival dates were analysed.

There was a significant relationship between first and mean arrival dates for 21 of the 28 study species but most relationships were weak. Further analysis showed first arrival was a reasonable proxy for mean arrival (and thus overall timing) for short distance migrants who had wintered in the Mediterranean and Northern Africa, such as Blackcap and Stonechat. It was a much poorer proxy for birds coming to the UK from Sub-Saharan Africa, such as the Sedge Warbler and Chiffchaff.

This study demonstrates the issues with using “first event” metrics, which has implications for numerous studies across biology. First event metrics can be useful and in some cases are the best we have, but should be interpreted with caution if the aim is to quantify overall [average] timing. These insights would not have been possible without a long-term dataset, such as the one at Portland, and this really demonstrates the value of such recording. The project was also very successful at bringing together academic researchers, students and external partners in a research team. Everyone bought different skills and expertise (and the students got a great CV booster!).

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More on this can be found on the British Ornithologists’ Union Blog at http://www.bou.org.uk/phenology-goodenough/

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