How birds navigate barriers to long-distance migration
Every year, millions of birds migrate around the world. In doing so, they must overcome certain ecological barriers in the landscapes, such as oceans and deserts. The success of a bird’s migration, and therefore its ability to survive, depends on the behaviour it uses to cross these difficult terrains. How songbirds do this has been debated for a long time. Songbirds usually fly during the day and rest at night, and it was unclear whether they change their behaviour. The BIRDBARRIER project, undertaken with the support of the Marie Skłodowska-Curie Actions, has been using groundbreaking tracking technology to investigate this issue. “This project aimed at describing in detail the behavioural changes birds show when crossing barriers,” says Sissel Sjöberg, a postdoc at the University of Copenhagen and BIRDBARRIER project lead.
Tracking advances
Until recently, studying the behaviour of small animals such as songbirds throughout migration has been particularly difficult. Either the tracking technology was too large to be carried, or the resolution of the data was too small to draw accurate or firm conclusions. The BIRDBARRIER team has been involved in the development of a new technology which makes this sort of tracking possible. These are miniaturised multisensor dataloggers that, as long as they stay on a bird, continue to record data. These loggers are customisable, and changing the sensors attached to the device alters which information it can gather. “The dataloggers we have used have recorded acceleration with a resolution of 5 min, which we translate into activity. This makes it possible for us to calculate, for example, exact flight times and durations. We also have a barometric sensor which gives us hourly information on flight altitude, interpreted from air pressure and temperature,” Sjöberg explains. The dataloggers used by the BIRDBARRIER team also have attached light sensors, which can gather information on sun hours, and approximate the position of the bird. “We can say where the birds are, at least during stationary periods, along with how much time they have spent on migratory flights. We can tell when they flew and how the birds have regulated flight altitude throughout the flights,” adds Sjöberg.
Behavioural changes?
Preliminary data from the project reveals that birds do behave differently at barrier segments compared to other migratory segments. “Nocturnally migrating species shift behaviour when crossing inhospitable areas, and sometimes instead fly both at night and during the day to get over the area as fast as possible,” says Sjöberg. The next step is to continue to publish the large amount of data that has been collected by the project, and also to try and understand the reason for, and importance of, the completely new behaviours that have been described through the project. In the long term, the team wants to continue the research, investigating how flexible these new behaviours are and how they might be adapted to a changing environment in the years to come.
Team collaboration
Sjöberg concludes: “Being allowed to work with data when we for the first time get insight into how individual birds behave throughout the annual cycle, and during their amazing journeys, is extremely fascinating, and everyone involved in the project has been amazed by the data we managed to get.”
Keywords
BIRDBARRIER, bird, migration, behaviour, changes, barrier, desert, ocean
