Alexander Lees

                                                                                                                                              Yellow-browed Warbler (Phylloscopus inornatus) North Ronaldsay, Orkney, 2008. 

As heterothermic volant organisms, birds have a higher capacity for long-range active dispersal than any other group. Birds are also the best studied of any taxonomic group and owing to the armies of rare bird enthusiasts out there who actively search for rare birds, we have a good record of the frequency and timing of occurrence of out of range 'vagrant' individuals - at least in Western Europe and the United States where observer density is high. The importance of the study of vagrants has often been dismissed, but understanding the patterns and mechanisms of such occurrences is incredibly important to fill the gaps in our knowledge on rare and extreme dispersal events. Although such movements may not happen often, they give rise to new breeding or wintering subpopulations in Continental and Island systems, eventually leading to speciation (especially in the latter case). Long-term data sets on vagrant birds may provide evidence for historic changes in population sizes before breeding areas were monitored. Understanding why some vagrant birds make navigation errors may provide further clues to unravelling the complexities of avian orientation.

My own research principally concerns the mechanisms which lead to vagrancy events and understanding the interspecific and inter-familial rates of vagrancy. The best data sets are all from the Holarctic where observers have been consistently present but increased birder presence at disparate locations throughout the world will hopefully facilitate a meta-analysis of vagrancy across island groups. Such long range dispersal events may be critical for the survival of many species in the face of anthropogenic climate change if they are not ecologically plastic enough to survive within their current ranges. 

Key papers:   

Lees, A.C. & Gilroy, J.G. 2004. Pectoral Sandpipers in Europe: vagrancy patterns and the influx of 2003. British Birds, 97: 638 – 646.

Gilroy, J.G. & Lees, A.C.  2003. Vagrancy theories: are autumn vagrants really reverse migrants? British Birds, 96: 427 – 438 PDF

McLaren, I. A., Lees, A.C., Field, C. & Collins, K.J. 2006. Origins and Characteristics of Nearctic Landbirds in Britain and Ireland in Autumn: a Statistical Analysis. Ibis, 148: 707-726 PDF

                                                                                                                                                                     Wallcreeper (Tichodroma muraria) Hecho Valley, Spain, 2001.