The migration behavior of starlings appears to be hereditary and not learned

Young, naive starlings search for their wintering areas independently of experienced conspecifics. Starlings are very social birds all year round, but that does not mean that they copy each other’s migration routes.

By revisiting a classic “relocation” experiment and adding new data, a team of researchers from the Netherlands Institute of Ecology (NIOO-KNAW) and the Swiss Ornithological Institute (Vogelwarte Sempach) has settled a long-running debate. Their findings are now published in the journal Biology Letters.

The question of how migratory birds determine their migration routes has intrigued mankind for centuries. Dutch biologist Albert Perdeck wanted to find answers when he flew thousands of migrating starlings from the Netherlands to Switzerland and Spain in the 1950s and 1960s.

This experiment has become a classic study of bird migration. Now, 70 years later, colleagues have confirmed his findings and were able to resolve a long-standing scientific debate using this historical dataset.

The birds were individually identified using lightweight metal leg rings with a unique code, a method still used today by the Dutch Center for Avian Migration and Demography, Vogelwarte Sempach and European partners. Ring recoveries indicated that translocated juvenile and adult starlings used different strategies to reach their wintering destinations in the British Isles and France.

“Adult starlings were aware of this movement and adjusted their migration direction to reach their normal wintering areas,” says Morrison Pot of the NIOO-KNAW. “Young starlings continued to fly in a southwesterly direction – the direction they would have chosen when leaving the Netherlands – and reached ‘wrong’ destinations in southern France and Spain.”

Over the years, bird migration experts have been divided over the interpretation of Perdeck’s results. Pot states: “Starlings are very social animals and according to some experts, the relocated young starlings could just as well have joined a group of local conspecifics.”

The relocated starlings would have copied the migration behavior of their new friends and shown them where to go. “If true, the migration route is largely learned rather than inherited”—a big difference.

The team of researchers retrieved the historical data of Perdeck’s translocation experiments from the paper archives of the Netherlands Centre for Bird Migration and Demography and compared the migration direction with the migration behaviour of local Swiss and Spanish starlings. “The latter data were retrieved from institutional archives, but were not available in Perdeck’s time.”

By re-analyzing this historical dataset, the team showed that the migration direction of the relocated starlings differed from that of their local counterparts. Starlings are therefore not social migrants or “copycats”. The alternative social explanation of Perdeck’s results is therefore disproved. As Pot explains: “Starlings travel independently and decisions about where to go are not overridden by the migratory behaviour of others.”

Recently, a study in collaboration with Vogelwarte Sempach showed that starlings migrate at night. This is consistent with the 70-year-old findings, because how would you follow someone in the pitch-black night?

Learned or inherited behaviour, why is it important? “In times of rapid changes in global climate and land use, it is of great importance to understand whether migration behaviour is largely inherited or learned,” says lead scientist and head of the Netherlands Centre for Bird Migration and Demography Henk van der Jeugd.

Inherited behavior is less flexible to rapid change. “Although starlings are abundant and widespread birds that have adapted to human-dominated landscapes, their migratory behavior is likely less flexible.”