Two subspecies of wheatear visit Helgoland: the nominate subspecies (oenanthe) breeds in most parts of Europe and Asia and in the western Nearctic, while the Greenland subspecies (leucorhoa) is confined to eastern Canadian, Greenland and Iceland. The migratory behaviour of these two subspecies of wheatear is vastly different: while oenanthe wheatears use many stop-over sites, leucorhoa wheatears make one of the longest transoceanic crossings of any passerine. This differential migratory behaviour is also evident in the stopover behaviour of birds on Helgoland, and has been the focus of study since 1998. To facilitate this study, birds are caught, ringed, colour ringed, measured and released. In addition, wheatear flight behaviour is studied by radio-tracking, radar and light-level geolocation.