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

Young, naive starlings are looking for their wintering grounds, regardless of experienced relatives. Starlings are very social birds throughout the year, but this does not mean that they copy each other’s migration route.

By revisiting a classic “displacement” experiment and adding new data, a team of researchers at the Netherlands Institute of Ecology (NIOO-KNAW) and the Swiss Ornithological Institute (Vogelwarte Sempach) have resolved a long-standing debate. Their findings have now been published in the journal Biology Letters.

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

This experiment has become 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 identified using lightweight metal leg rings with a unique code – a method used by the Netherlands Center for Bird Migration and Demography, Vogelwarte Sempach and European partners to this day. Ring recoveries showed that young and displaced adults used different strategies to reach wintering destinations in the British Isles and France.

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

Over the years, experts in the field of bird migration have been divided about the interpretation of Perdeck’s results. Pot says: “Starlings are highly social animals and, according to some experts, displaced young starlings may just as well have joined a herd of native relatives.”

The displaced stars would have copied the migratory behavior of their new friends by telling them where to go. “If true, the migratory pathway is largely learned rather than inherited” – a big difference.

The research team found historical records of Perdeck’s translocation experiments in the paper archives of the Dutch Center for Migration and Bird Demography and compared the migratory orientation with the migratory behavior of the native Swiss and Spanish starlings. “Recent records were obtained from institutional archives but were not available at Perdeck’s time.”

By reanalyzing this historical data set, the team showed that the migratory orientation of displaced starlings differed from their native relatives. Thus, stars are not social migrants or “copycats”. The alternative social explanation of Perdeck’s results is thus invalidated. As explained by Pot, “Stars 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 stars migrate at night. This is consistent with the 70-year-old findings, because how would you follow 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 of great importance to understand whether migratory behavior is mainly inherited or learned,” says lead scientist and head of the Netherlands Center for Aircraft Migration and Demography, Henk van der Jeugd.

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