Is a bird’s migratory behaviour innate? No, says a study by UG ecologists Theunis Piersma, Jelle Loonstra, and Mo Verhoeven. The study was recently published in Current Biology.
‘Some biologists assume that birds are these pre-programmed machines, who know from birth where they’re supposed to go. That’s the genetic approach’, says co-author and migratory bird ecologist Theunis Piersma. ‘We’ve proven that this isn’t ture. Godwits learns the migratory route and their destination from their fellow birds or their environment.’
The godwit nests where the chicks for this study came from were located in fields in the southwest of Friesland. The chicks there have the smallest chance of surviving by natural means, says Piersma. ‘There isn’t enough food, and the birds there get eaten fairly often.’
Two groups
The eggs were hatched, and the researchers raised the chicks. When they were ready to start flying, the researchers split the group in two. One half stayed in Friesland, and the other half was taken to the nesting site of a different colony, a thousand kilometres away in Poland.
The birds were then released just in time for migration. If migratory routes and destinations were innate, the ‘Frisian’ group in Poland should have wanted to return to the route the Dutch birds usually fly.
Transmitters were attached to the birds’ backs to track them. The Frisian godwits were also outfitted with trackers. Both groups were released during the breeding season.
Winter
The Frisian birds took the usual western route to the wintering grounds in Africa, while the godwits from Poland took a different, eastern route. They also didn’t winter in the same place in Africa.
That means, says Piersma, that godwits probably learn from their environment. ‘It’s easier for the birds to adapt to a change in suitable areas than we initially thought.’
That means there’s hope, says Piersma. ‘In case of a habitat change, individual birds that display the wrong innate behaviour won’t necessarily be the first to die. They can learn a different route.’
Other bird species
The study also sheds light on other bird species, Piersma thinks. ‘While godwits leave the nest very early, birds such as geese, swans, or cranes can stay with their parents up to two years. We now know that’s when they learn the migratory route.’
The question now remains who teaches godwits the route to the wintering grounds, Piersma says. ‘Is it older birds? Or maybe even an entirely different species of bird, such as the ruff?’
Trackers
A follow-up study will focus on answering this question. ‘We’re looking into the option to put a tracker with a microphone and a camera on the birds. We’d then be able to study the animals’ social environment.’
Because trackers like these would be a little too big for godwits, they’ll probably start with a different species of bird, says Piersma. ‘We’re now considering spoonbills. They’re larger, but their behaviour is very similar to that of godwits.’