Birds observed outside their normal distribution range, vagrants, have fascinated bird watchers for more than a century. The causes behind vagrancy are probably many but not well understood. External drivers, such as strong winds or disturbance of the geomagnetic field may affect otherwise normally migrating individuals outside their range. For example, birds raised in areas with magnetic anomalies might become primed to set out along an abnormal direction (Alerstam and Högstedt 1983). Alternatively, it has also been speculated that the innate compass or goal might become mis-programmed due to genetic or ontogenetic errors, thus sending migrants in scattered directions though these will only be recorded as vagrants along routes where they can survive and be observed. Some species seem much more prone to seed vagrants to western Europe than others. For example, the Pallas’ leaf warbler Phylloscopus progegulus is ~5 times more common as a vagrant in the UK compared to the greenish warbler P. trochiloides, despite its breeding range being located >4000 km further east. Though the overall number of Siberian vagrants reaching western Europe may correlate with easterly winds, the relative proportion of the species occurring as vagrants can differ strongly between years, e.g. peak years of Palla’s leaf warblers do not coincide with peak years of Radde’s warblers P. schwarzii.
The aim of this project is to explore various variables that can explain why some species are more common as vagrants than other species. These variables may include range size, abundance, migratoriness and phylogenetic relationships. The methodology for the project will be similar to a recent study about wintering range evolution of long distance migrants (Bensch et al 2023). For the project, you will construct a database from the literature to quantify “vagrancy” and relevant species traits, and use phylogenetic comparative models for the analyses.
Supervisor: Staffan Bensch staffan.bensch@biol.lu.se
References
Alerstam, T. & Högstedt, G. 1983. “The role of the geomagnetic field in the development of birds’ compass sense.” Nature 306: 463-465.
Bensch, S., Caballero-Lopez, V., Cornwallis, C. K. & Sokolovskis, K. 2023. The evolution of “suboptimal“ migration routes. iScience 26, 108266.