As winter edges closer, the GWCT’s Dr Andrew Hoodless considers the arrival of migrant woodcock and emerging technologies for tracking birds to and from their breeding grounds
While we all eagerly await the arrival of migrant woodcock in autumn, this is not always the case, however, and in the right place at the right time, the spectacle of large numbers can be just as impressive as in autumn.
I have heard several reports from the eastern counties, particularly Norfolk, over the years of woods lifting with birds for one or two days in March. Recoveries of ringed woodcock abroad indicate that the last migrant woodcock are here until 15th April, though my observations suggest that most disappear in mid-March. Interestingly, resident males often commence their distinctive ‘roding’ displays at dawn and dusk in late February in southern England and clutches of eggs may be complete in March.
Early radio-tracking studies by the then Game Conservancy Trust, showed that woodcock males do not hold territories and do not pair for the breeding season in the way that most other waders and woodland birds do. Instead, roding males patrol areas of suitable breeding habitat in seek of receptive females and the older, dominant males may mate with up to four females in a season. Hence, it is possible that foreign males could rode here and even mate with British females before departing. However, this would incur an energetic cost and it is more likely that they are pre-occupied with getting into condition for the flight back to breeding grounds further afield, near their hatching location. There are no records of foreign-ringed woodcock ever being found in Britain or Ireland in the breeding season. However, roding by woodcock on migration has been documented in the French-Swiss Alps.
Inevitably, woodcock migrating to the far northern and eastern breeding grounds may have to wait for snow and ice to thaw before reaching their final destinations. Hence, in northern Scandinavia and Russia, breeding typically commences at least a month later than in Britain and the breeding season is consequently shorter. Even on the southern European Plain in Russia, for instance, woodcock may not return until early May, but the first eggs can be found within 5-6 days of the birds’ arrival.
For over a century, sportsmen have speculated about the origins of the woodcock they see in winter and looked for possible clues in the colouration of the plumage. Our analysis of isotopes in feathers is starting to provide information on the origin of migrants at a broad geographical scale, but we still know very little about the routes taken by individual birds back to the main breeding grounds in Russia, Belarus and Scandinavia or the time taken to reach them. However, new technologies are opening up exciting possibilities for discovering this. Satellite tracking is a well-established technique for following larger species, such as swans and geese, but satellite tags are now small enough to follow birds like woodcock. However at £3,000each, this technology is not cheap.
A Spanish team from the Club de Cazadores de Becada, the national woodcock hunting association, was the first to fit a woodcock with a solar-powered satellite tag in the Basque country in February 2006. They have since fitted tags to five more woodcock. Their results are fascinating, showing that birds wintering in this region travel to north of Moscow to breed. One bird, ‘Navarre’, a juvenile female tagged in March 2007, has twice migrated to Russia and back to Cantabria, completing the 3,800km spring trip in ten weeks. In winter, she has returned to within 11 km of her tagging location.
In late February 2009, Roy Dennis in Scotland fitted two woodcock with satellite tags on Islay on the same night. What is interesting about his observations is the difference in the behaviour of the two birds. The first left Islay on the night of 22nd March and proceeded to cross mainland Scotland during the next five days. Sometime between 27th and 30th March it crossed the North Sea to Norway and from 4th April was presumed breeding near Mandal in southern Norway. The second bird first travelled south and was in Humberside on 25th March, from where it proceeded on a journey of at least 4,110km to northern Russia via Germany, the east coast of Sweden, Latvia, Estonia and then across Russia to the east of St Petersburg and Arkangel. It finally settled on its breeding site two months after departing, on 27th May, at 68°N, 45°E, near the northern limit of the species’ breeding range!
Returned from Cornwall in March, where I have fitted woodcock with geolocators. These tags are much smaller and cheaper than satellite tags and have the potential to yield similar information on migration routes. They have been used successfully to follow arctic terns to Antarctica and work by logging daylight levels, from which the time of sunset and sunrise can be determined and hence latitude and longitude can be deduced to an accuracy of about 100km. I’m conducting a trial with 25 tags and collaborating with Yves Ferrand at the Office National de la Chasse et la Faune Sauvage, who is attaching 25 to woodcock in France. In Autumn,2010, we are hoping to catch birds in West Wales and fit them with geolocators as well. Working closely with the Woodcock network, birds are already being captured for ringing and so we hope to add geolocators to a sample of them this winter.
Both types of tags have their limitations. Satellite tags only transmit locations periodically and yield information of variable accuracy owing to their solar charging. Geolocators need to be retrieved to download the data. Nevertheless, technological refinements are continually being made and I am convinced that in a few years we will have some revealing insights into the migration strategies of woodcock across Europe. This information is essential for sound conservation management of the species, as well as being of fascination to us all.