Quantifying the robustness of first arrival dates as a measure of avian migratory phenology

• Published in: Ibis (London, England) England), 2015-04, Vol.157 (2), p.384-390
• Main Authors: Goodenough, Anne E., Fairhurst, Stacey M., Morrison, Julia B., Cade, Martin, Morgan, Peter J., Wood, Matt J.
• Format: Article
• Language: English
• Subjects: Bird migration; climate change; mean arrival dates; migration; Phenology; timing
• ISSN: 0019-1019; 1474-919X
• DOI: 10.1111/ibi.12227

As the climate changes, many long‐term studies have shown that the timing of bird migration is shifting, increasing the need for reliable measures of migratory phenology. Ideally, daily counts of birds at a site are used to calculate the mean arrival date (MAD) but, as this approach is not always possible and is very labour‐intensive, simpler metrics such as first arrival date (FAD) have commonly been used. Here, we examine the relationship between FAD and MAD in 28 summer migrant bird species over a 42‐year period (1970–2011) at Portland Bird Observatory, UK. Although significant correlations between FAD and MAD were detected, relationships were weak, particularly in long‐distance migrants. We suggest that FAD, although a simple and straightforward measure, is not particularly robust as a proxy for overall migratory phenology at a population level.