Great Snipe bonanza

A so-called ’geolocator’ is a minute electronic device that logs light intensity over time. As the sun rises at different times at different longitudes, and as the length of day varies with latitude, light records can be used to derive the approximate location of the loggers on the globe (± 300 km). The latest geolocator model only weighs 1 gram. This has opened the exiting opportunity to track, for the first time, the migrations of small passerine birds (see Stutchbury et al. 2009). One important limitation of geolocators is that these tags have to be retrieved in order to obtain the data. The technique can thus only be used for birds that are faithful to their breeding site.

Example of a light registration over time from which location estimates can be derived.

While discussing the use of geolocators the Great Snipe was one obvious candidate species. Very little is known about the migration habits and wintering quarters of this endangered Swedish breeding bird. For example, no ring recoveries are known from Africa, the region where Scandinavian birds are supposed to spend the winter. Great Snipes return to their breeding areas, and thus geolocators can indeed be used to reveal their migratory movements and wintering areas. We decided to start a pilot project and to apply geolocators on 10 Great Snipes. We choose to work in Jämtland (near Enafors/Storlien) where people from the Ånnsjön bird observatory know the local Great Snipe population very well.

Great Snipes are best caught at so called ‘leks’, traditional places where males assemble at dusk to display. As females only visit the leks to pair, and are thus more difficult to catch in a subsequent year, we decided to focus on males. People from the bird observatory were especially interested in females as they aim to track them during the breeding season to find out where they breed and where they raise their young. So males for geolocators, females for radiotransmitters. Would the three nights that we had planned be enough to capture 10 males?

The first evening we visited a lek (Sträton) a few kilometres from the Storulvan tourist station. With the help of a GPS we located the centre of the snipe lek. Here and not 50 metres to the left or right the Great Snipe show would happen tonight. We encircled the lek with special wader mistnets. This type of net is the most efficient to catch larger birds as the net is less visible and the birds get well entangled. As soon as the sun set the Great Snipes arrived to the lek and started to display. By walking the lek the birds could be flushed into the nets. This turned out to be an extremely efficient way to catch. The first night we already caught 21 birds! In fact we believe that we caught all the males that were present at this lek. Already after 3 hours of catching all 10 geolocators were applied, mission completed. Six out of the 21 birds were females, thus we could also apply six radiotags. The hardest part of the job was probably that we had to walk all the way back with all the equipment as we were exhausted after a night of catching. It must have been the unbeatable singing Bluethroats that kept us on our feet...

Walking uphill with all the catching equipment

View on one of the leks where we caught birds.

Peter Carlsson from the Ånnsjön bird observatory is extracting a snipe from the net.

One of the Great Snipes in the hand. Note the moult contast in the primary coverts.

Great Snipe with a geolocator mounted on the leg ring.

The happy field team procesing birds. Great teamwork!

In the subsequent two nights we visited two other leks. Catching was at least as efficient there. The unofficial world record in catching Great Snipes is now set at 24 birds per night! In total we caught 52 birds during three nights. Eight of these were already ringed in previous years (controls). Twelve birds were females. A great success for a relatively short visit!
Next year is going to be even more exciting as we then we hope to recapture some of the males at their lek. Will the Great Snipe finally reveal its migration habits?

Some relevant links:
Geolocators are produces by BAS: www.birdtracker.co.uk
Stutchbury et al. (2009): www.sciencemag.org/cgi/content/abstract/323/5916/896