About the Woodcock
Current knowledge of woodcock origins and migration
Current knowledge of woodcock migration is based on recoveries of ringed birds. To date, information on the origins of birds wintering in Britain and Ireland
is based on small numbers of foreign ring recoveries. While ringing data provide vital information on bird movements, they are dependent on the number of birds
ringed and recovered. A new ringing initiative by the Woodcock Network should change this during the next few years. However, foreign recoveries of British-ringed
woodcock need to be interpreted with care owing to historical changes in shooting seasons and the fact that some countries still permit the shooting of roding
birds in the spring.
The use of intrinsic markers, such as stable isotopes, offers an alternative approach to ringing. Stable isotope analysis enables the hatching or moulting location of a bird to be estimated from the chemical composition of its feathers. Although the resolution of the technique is limited to several degrees of latitude and longitude, it has the considerable advantage over ringing that birds do not need to be marked and subsequently recovered, but that any bird can provide a sample. A three-year study at the GWCT employing this technique will be completed in April 2012 and is starting to yield interesting results.
Ringing and stable isotope analysis suggest broadly similar compositions of the British and Irish wintering woodcock population, with approximately 17% being British breeders, 51% originating from Russia and the Baltic states and 32% from Scandinavia and Finland. The data suggest that woodcock from Russia and the Baltic States travel to Britain across a broad front, whereas Scandinavian birds appear more restricted to Scotland, Wales and Ireland, with a lower proportion reaching southern England. What ringing and stable isotope analysis cannot provide is detailed information on the routes flown between breeding and wintering areas; for this individual birds need to be tagged and followed.
In March 2010, we started fitting woodcock with geolocators, miniature tags that store information on light levels. Geolocators are small, relatively cheap, and enable sunrise and sunset times to be estimated and hence latitude and longitude to be calculated to an accuracy of about 150 km. They have the disadvantage that the bird needs to be recaptured to retrieve the tag and download the data. During March 2010 and March 2011, we fitted tags to a total of 51 woodcock at a site in Cornwall and have recovered seven of these to date. They have provided fascinating insights into the timing and speed of migratory flights, with four birds travelling to Scandinavia, two to Russia and one to Belarus. It is apparent that woodcock are able to fly non-stop at an average speed of 40 km/h for up to 24 hours, but break their migrations with stops of 11-17 days.
The major advantage of satellite telemetry over other techniques is that it enables us to track woodcock over long distances in near real time, without requiring the need to ever recapture the bird. Satellite tags have been successfully trialed in Spain and Scotland (see http://rtvs.ccbp.org/index.php, http://www.roydennis.org/birds/index.asp?id=135). The Spanish team from the Club de Cazadores de Becada have been able to follow woodcock from the Basque region of Spain to the Baltic and have managed to track one bird there and back in two consecutive years. One bird tagged in March 2010 made a 6100 km trip to breed in central Russia! In Scotland, Roy Dennis fitted two satellite tags to woodcock on Islay in March 2009. Interestingly, these birds undertook quite different migrations. One bird crossed mainland Scotland and the North Sea to a breeding site in Norway, taking two weeks to get there. The other bird made its way to NW Russia, migrating first south through northern England, across to Germany, then through Latvia and Estonia and finally reached its breeding site two months later. Both studies suggest that satellite tagging will prove a valuable tool in the study of woodcock movements.