Experience and motivation shape the flight performance of white storks migrating long-distance

Abstract

Movement allows animals to access resources and pursue fitness. Yet, this requires balancing movement costs against other potential benefits. These trade-offs can change over lifetimes, as optimality is contextual and depends on ability and need. For migratory soaring birds, efficient movement requires exploiting atmospheric uplift— a challenging task that negates the cost of flight. Due to this link between costs and the environment, soaring birds are limited in when and where they fly. Thus, soaring performance goes beyond movement skills and also involves coping with potentially imperfect conditions to reduce time or competition. Here, we asked whether, over repeated migrations, white storks (Ciconia ciconia) improve their ability to soar. Using high-resolution lifetime tracking data from 151 storks, we found that juveniles outperformed adults under supportive conditions, but, with age, migration difficulty increased and adults performed well under challenging conditions. Adults traveled in less-supportive conditions and spent more energy on flight, indicating a change in ability and motivation. Thus, understanding how animals improve is not simply described by a learning curve but requires a multifaceted perspective on individual needs and skills.