Earlier spring staging in Iceland amongst Greenland White-fronted Geese Anser albifrons flavirostris achieved without cost to refuelling rates

Abstract

Greenland White-fronted Geese wintering in Ireland and Britain stage for 3 weeks in Iceland in spring before migrating onwards to breeding areas in west Greenland. The geese now depart their wintering quarters 12–15 days earlier than in 1973 because they attain necessary fat stores earlier than in previous years. Icelandic temperatures at critical midway staging areas have shown no significant change since 1973, creating a potential mismatch in food availability along the migratory route. Greenland White-fronted Geese have shifted from consuming below-ground plant storage organs in Iceland in spring to grazing managed hayfields created since the 1950s where fresh grass shoot growth occurs despite sub-zero temperatures, when traditional natural foods are physically inaccessible to staging geese due to frozen substrates. Rates of fat accumulation (measured by field scores of abdominal profiles) and mass change (measured in captured geese) were the same in the springs of 1997, 1998 and 1999 as in that of 2007 when the migration episode was 10 days earlier. Hence, earlier arrival in Iceland in 2007 did not occur at cost to refuelling rates there. The shift to acquiring energy from artificial grasslands has enabled Greenland White-fronted Geese to arrive in Iceland earlier, but has apparently not impaired their ability to accumulate fat reserves required for onwards migration, which occurs at the same rate, only earlier in the spring.