| Abstract: | Greenland white‐fronted geese accumulate body mass throughout late winter in preparation for migration after mid‐April to spring staging areas in Iceland. This analysis presents field assessment of abdominal fat deposits (API) from large samples of marked birds which showed increasing rates of fuel deposition throughout January–April. Historical records show that geese rarely depart en masse before 17 April, a pattern followed by all but one of the tagged birds. Timed positions obtained from 12 geese fitted with satellite transmitters in 1997, 1998 and 1999 suggested that all geese departed winter quarters on tailwinds between 16 and 19 April. Tracked geese flew directly to staging areas in Iceland, although one staged for 10 days in Northern Ireland in 1997 and another may have stopped briefly in western Scotland. Average migration duration of all tagged birds departing Ireland (including the 1997 bird that stopped over within Ireland) was 25 hours (range 13–77). Four geese apparently overshot and returned to Iceland during strong E to ESE winds. APIs in Iceland showed more rapid and linear increases in stores during the mean 19‐day (range 13–22) staging period there than on the winter quarters. Geese continued their migration to Greenland when APIs attained or exceeded levels at departure from Ireland and all departed on assisting tailwinds between 1 and 11 May. Tracked birds continued the journey to West Greenland in between 24 and 261 (mean 82) hours, although one bird turned back during the traverse of the Greenland Ice Cap and summered on the east coast. Seven of the birds staged for 1–20 hours at, or near, the East Greenland coast and several made slow progress crossing the inland ice, all in the direction of their ultimate destination (i.e. not necessarily taking the lowest or shortest crossing routes). It is suggested that the energy‐savings of departing on tailwinds may favour geese to wait for such conditions once threshold fat storage levels have been reached, but more research is needed to confirm this. |
