Timing rather than movement decisions explains age-related differences in wind support for a migratory bird

Migratory birds must make complex decisions to use wind their advantage during flight and increasing performance is particularly important while crossing ecological barriers. Age-related differences in how deal with have suggested experience improves necessary skills gaining positive support. However, support between age groups over barriers rarely been tested, our understanding of acquire related lacking. We compared achieved by adult subadult Caspian terns, Hydroprogne caspia, southward northward crossings the Sahara Desert quantifying air-to-groundspeed ratios (AGR). also tested possible underlying causes lower comparison adults calculating optimal AGR altitudes fitting step selection functions response direction speed. found no difference autumn, when young were flying adults, but subadults had first solo crossings. Adults departed northwards from wintering areas earlier year encountered more favourable conditions than subadults, yet both made similar movement relation wind. Consequently, are better explained timing passage rather skills. Our findings highlight influence seasonality on migratory behaviour raise questions about evolution ontogeny patterns other factors that may determine departure decisions.