The migratory behavior of starlings has been found to be inherited, not learned

Young, naive starlings search for their wintering grounds independently of experienced species. Starlings are highly social birds all year round, but this does not mean that they copy each other’s migration route.

A team of researchers from the Netherlands Institute of Ecology (NIOO-KNAW) and the Swiss Ornithological Institute (Vogelwarte Sempach) settled a long-standing debate by rethinking the classic “displacement” experiment and adding new data. Their findings are now published in a journal Biology letters.

The question of how migratory birds locate their migration routes has fascinated mankind for centuries. Biologist Albert Perdeck of the Netherlands tried to find answers when he airlifted thousands of migrating starlings from the Netherlands to Switzerland and Spain in the 1950s and 1960s.

This experiment became a classic study on the migratory orientation of birds. Now, 70 years later, colleagues have confirmed his findings and have been able to resolve a long-standing scientific debate using this historic data set.

The birds were individually identifiable using light metal leg rings with a unique code – a method still used today by the Netherlands Center for Bird Migration and Demography, Vogelwarte Sempach and European partners. Ring recovery showed that translocated young and adult starlings used different strategies to reach wintering destinations in the British Isles and France.

“Adult starlings were aware of this movement and adjusted their migration orientation to reach their normal wintering grounds,” says NIOO-KNAW’s Morrison Pot. “The young starlings continued in a south-westerly direction – the direction they would have taken when departing from the Netherlands – and reached ‘wrong’ destinations in southern France and Spain.”

Over the years, bird migration experts have disagreed on the interpretation of Perdeck’s results. Pot states: “Starlings are highly social animals, and some experts believe that relocated young starlings may as well have joined a flock of local species.”

The displaced starlings would mimic the migratory behavior of their new friends, who would show them where to go. “If true, the migration route is largely learned rather than inherited” – the main difference.

The research team obtained historical data of Perdeck’s relocation experiments in the paper archives of the Netherlands Center for Bird Migration and Demography and compared the migratory orientation with the migratory behavior of local Swiss and Spanish starlings. “Recent data was obtained from institutional archives, but was unavailable in Perdeck’s day.

By reanalyzing this historical data set, the team showed that the migratory orientation of the relocated starlings differed from their local counterparts. Starlings are not social migrants or “copycats”. An alternative social explanation for Perdeck’s results was thus revealed. As Pot explained, “Starlings travel independently, and decisions about where to go are not overridden by the migratory behavior 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 track someone in the dark of night?

Learned or inherited behavior, why does it matter? “In times of rapid changes in global climate and land use, it is very important to understand whether migratory behavior is largely inherited or learned,” says lead scientist and head of the Netherlands Center for Bird Migration and Demography Henk van der Jeugd.

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