Spring weather and the migration of geese from Scotland to Iceland

Abstract

Records of first arrivals of geese at sites in Iceland between 1950 and 1997 are combined with dates of departures from Scottish roosts and flights seen over northern Scotland to identify when migratory movements occurred. Greylag Geese Anser anser moved earliest, the mean date of first sightings in Iceland being 3 April (s.d.14.3 days) and of northward movements over Scotland 14 April (s.d. 12.9 days), the median first arrival and departure dates being 8 and 15 April. The mean date of first sightings in Iceland of pink-footed geese Anser brachyrhynchus was 13 April (median 21 April) and of Scottish departures 20 April (median 25 April). The mean dates of Scottish departures and Icelandic sightings of Greenland White-fronted Anser albifrons flavirostris, Barnacle Branta leucopsis and Brent geese Branta bernicla all lay between 18 and 22 April, with median dates from 19 to 27 April. Arrivals in Iceland were associated with anticyclonic conditions over Scotland on the previous day, while cyclonic conditions were avoided. There were more sightings over Scotland when conditions were unfavourable than would be expected from the frequencies of those conditions in April. There were unexpectedly few movements around dates of full moons (+/- 2 days). The three grey geese, but not the black geese, have tended to arrive in Iceland earlier in recent years. Head and westerly winds were far more frequent than tail winds, especially after 1970, and there is some evidence of eastward drifting, yet the energetic demands of the flight from Scotland to Iceland can rarely have been severe.