This article shows some amazing data on Great Snipe autumn migration - http://planetearth.nerc.ac.uk/news/story.aspx?id=983
'After the breeding season, but before the annual migration, the researchers fitted 10 male great snipes at Jämtland in Sweden with a geolocator each. Exactly a year later, the scientists managed to retrieve three geolocators from three birds when they returned to Sweden after their northward migration.
Klaassen and his colleagues found that one bird flew 4225 miles (6800km) from Sweden to central Africa in just 3.5 days. The other two birds flew 3833 miles (6169km) in three days, and 2870 miles (4619km) in two days.
'We think maybe the feeding conditions are so good in Scandinavia, the birds take advantage of the opportunity to feed up,' Klaassen says.'
'After following the birds' migration south from Sweden to central Africa using tiny tracking devices, Swedish scientists found that the birds fly non-stop over a distance of around 4200 miles (6760km) at a phenomenal 60mph (97kmh).'
Great snipes breed in Scandinavia from mid-May to early-July. The birds leave their breeding grounds from early-August onwards. The return northward migration happens between March and April. No wonder not many turn up in the UK...