[1] Alaska Dept Fish & Game, Fairbanks, AK 99701 USA
[2] Environm Canada, Beaverhill Bird Observ, Tofield, AB T0B 4J0, Canada
[3] Migrat Res Fdn, Ste Anne De Bellevue, PQ H9X0A6, Canada
[4] Canadian Wildlife Serv, Beaverhill Bird Observ, Tofield, AB T0B 4J0, Canada
[5] Hallkved, S-75597 Uppsala, Sweden
[6] Owl Res Inst, Charlo, MT 59824 USA
[7] US Fish & Wildlife Serv, Anchorage, AK 99503 USA
[8] US Fish & Wildlife Serv, Juneau, AK 99801 USA