For the sixth year in a row, researchers from CAnMove have been to the mountains in northern Sweden to study the migration of Great Snipes. By putting on small recording devices on the birds, so called geo-locators (“loggers”), we have been able to follow the birds from their breeding grounds in Sweden to the wintering grounds in central Africa. We have learned that they make most of the autumn migration in one go, flying 6000 km or more non-stop to northern Nigeria. A few weeks later they continue to the final winter stay around the Equator.
The males gather on “leks”, with 5-15 males that display through the night to attract females for mating. This is when we trap the birds. Our hopes this year was to get back some of the 16 loggers that we put on last year. These new loggers carry a temperature sensor, which potentially could add new exciting information. But, again, we need to catch the birds back… Already the first evening out we managed to spot and even photograph two lekking birds that carried loggers. The orange and black you can see on the leg of the displaying bird is a logger attached to a ring.
By splitting up in two teams we could visit two leks at a time. We struck it rich already the first evening when we caught as many as eight birds with loggers! There was great excitement in the group when we gathered around our small wind shelter to process the birds. Surrounded by snow covered mountains and a choir of newly arrived Ring Ouzels and Bluethroats, we carefully processed the birds and took off the loggers.
Back at the field station we made a preliminary analysis of a few loggers and the results are stunning. The sudden and dramatic drop in temperature when the birds depart on their long flight, entering very cold air at heights of maybe several thousand meters, help us to know more when during a day the birds leave. Likewise, a few days later, the sudden shift from very cold high altitude flights to the heat of sub-Saharan Africa upon landing is striking.
New for this year was to employ satellite transmitters (PTTs) on three birds. A PTT weights 5 g and is put on the bird as a small backpack. It communicates with satellites that orbit the Earth and the batteries are recharged by solar cells. There are three great advantages with the PTTs. First, the precision with which we can determine the position of a bird increases immensely – from about ±200 km from the loggers to ±2 km. Second, we do not need to retrap the bird to get data. Third, we get data with a delay of only a few hours.
When we checked the focal lek a few days later, two of the birds could be seen displaying in the evening, seemingly unaffected by their small backpacks. We are now hoping eagerly that the coming year will bring us new exciting details about the great flights of the Great Snipes.
(Pictures by Thomas Alerstam and Åke Lindström).