Vårflyttning av taigasädgås Anser f. fabalis längs den ”västra flyttvägen” i norra Sverige: rastantal 2003—2008 och tidsmässig kulmination i jämförelse med den ”centrala flyttvägen” i Finland

Abstract

Daily counts and conservative estimates of turn-over showed that at least 3,000 Taiga Bean Geese regularly used the Ume River Delta as the major staging site along the Western Flyway (following the west coast of the Gulf of Bothnia) during spring 2003—2008. Counts across all staging sites yielded 2,700–3,700 geese in southern Västerbotten and 4,000–4,800 at all sites in Västerbotten and Norrbotten. We estimate that 5,000–6,000 geese currently use the Western Flyway. Migration along the Central Flyway (Ostrobothnia, Finland) culminated on average about ten days earlier, meaning that the vast majority of geese using this flyway had left southern Sweden when the Western Flyway was activated. Counts of active migration on 15 April 2007 indicated that geese arriving in the Ume River Delta in late afternoon had passed Alirs öga, Söderhamn, 340 km to the south, five hours earlier. Assuming the same ground speed (68 km h^-1) south of Söderhamn, these geese ought to have left either Lake Östen and/or Lake Kvismaren at sunrise, reaching the staging sites in Västerbotten after a 600–700 km non-stop flight.