People have long attempted to understand the behaviour of migratory birds. The life of seasonal birds appeared to be mystical. People therefore invented all kinds of reasons why birds vanished from time to time. As little as two hundred years ago, people in Nordic countries believed that, swallows overwintered in the bottoms of lakes, although theories about migration began popping up at the time. Barnacle geese were named after crustaceans called barnacles, as people in English-speaking Europe thought the geese were born from these barnacles. The geese disappeared for the summer, but barnacles were seen instead. Barnacle geese breed in the high Arctic, so gooselings were obviously never seen in Central Europe.
Bird ringing or banding began in Denmark in 1899, when Hans Christian Cornelius Mortensen marked his first starlings. Ringing became an important tool for bird research, aiming to study migration in particular.
Researcher Ib Krag Petersen continues a long tradition of Danish bird ringers. A red-breasted merganser (Mergus serrator) ringed in Iceland was controlled from her nest.
Ring discoveries help understand migration routes and phenology in addition to bird habitats. However, birds usually need to be captured to read the rings. This commonly means that ring recoveries are from birds found dead or birds that have been shot. Thus, bird ringing and death locations are generally the only information gathered from ringing efforts. However, new devices provide researchers with the opportunity to follow birds year-round.
Geolocators
Light-level geolocators are small devices developed for following bird migration. Geolocators measure daylight, which makes it possible to define the times of sunrise and sundown. Calculating the longitude is possible by measuring the difference in the timing of noon and the Greenwich meantime, and calculating the latitude is possible by measuring day length. However, location data accuracy is rather poor. Geolocators do not send data, so birds must be recaptured to collect the devices and obtain the data. This means that the method is laborious and suitable only for birds that are highly likely to return to certain locations. Geolocators are therefore usually attached onto philopatric female birds captured from their nests. Size is a good feature of the geolocators. They can be tiny (even under 0.5 g), which makes them suitable even for small birds. A rule of thumb for transmitter weight is generally a maximum 5% of the bird’s weight. Geolocators may also be used to measure other variables such as temperature.
Geolocators are used for example in Iceland to study the wintering areas of diving ducks. Diving ducks winter at sea, so following their movements otherwise is difficult. Ducks are philopatric and so females captured from their nest sites will probably return to the same place year after year. Therefore, a female captured and marked at her nest can be found again presuming she survives the whole year. Collected geolocators reveal where females have spent the rest of the year.
Ib Krag Petersen’s study area in northern Iceland is searched every year to locate duck nests. All diving duck females are captured and checked for old geolocators and if none are found, new ones are attached to the ducks. This long-tailed duck (Clangula hyemalis) female got a geolocator on her leg for the first time.
GPS trackers
Trackers utilizing GPS technology produce the most accurate and timely information. GPS trackers potentially collect very accurate knowledge about bird location but can additionally measure many other variables such as the elevation and activity of the bird. GPS trackers can either send data or just collect it. Trackers may be set to send data even once a minute if the bird is within a telecommunication network. Sometimes these connections cause surprises, as a group of Russian eagle researchers found out. The studied eagle left its normal habitat and spent long times outside the telecommunication network. When it came back to an area with a network, all the data gathered during the blackout was sent at once to the researchers in the form of expensive text messages from Iran.
GPS trackers often use small solar panels, which enable data collection and sending for several years. Because GPS trackers are heavier than geolocators, their use is limited only to larger birds. Trackers may be attached as neck collars or as backpacks. Under-skin implants are also an option.
Antti Piironen uses GPS trackers to observe geese flyways and habitats along the flyways. Visit the link to follow the migration route of this graylag goose here.
Several bird species, such as birds of prey, black-throated loons and geese, are followed with GPS trackers in Finland. For example, GPS birds have been used to study wintering areas and changes occurring in these areas. Geese trackers have revealed details of a geese moulting migration to Novaya Zemlya. The movements of Finnish birds can be followed on the webpages of the Finnish Museum of Natural History and the Finnish Biodiversity Information Facility.
Read more:
Waterfowlers’ network 21.1.2020: Unraveling migration patterns of Finnish Greylag Geese
BBC 25.10.2019: Migrating Russian eagles run up huge data roaming charges
Finnish Museum of Natural History
Finnish Biodiversity Information Facility
Oceanwide Expeditions: Barnacle Goose
Close Encounters of the Natural Kind 