Cultural transmission and flexibility of partial migration patterns in a long-lived bird, the great bustard Otis tarda

Factors responsible for individual variation in partial migration patterns are poorly known, and identifying possible causes of these changes is essential for understanding the flexibility in migratory behavior. Analyzing 190 life histories of great bustards Otis tarda radio-tagged in central Spain, we investigated the changes in migratory tendency across lifetime in this long-lived bird, and how migratory flexibility is related to individual condition. In females migratory behavior was not fixed individually. For every age class there was a fraction of ca 15-30% of females that changed their migratory pattern between consecutive years. Migrant females tended to remain sedentary in years when they had dependent young to attend. These findings show that the female migratory tendency is a behaviorally flexible, condition-dependent trait. Immature females usually acquired their migratory behavior by learning from the mother in their first winter or by social transmission from other migratory females in their second winter. As for immature males, their summer migratory behavior was not related to mother-offspring transmission, but learned from adult males. We found that their age-related increase in migratory tendency was associated to a greater integration in flocks of migrant adult males. These results show that within the partial migration system, cultural transmission mechanisms, either mediated by kin or not, and individual condition, may contribute to shape the migratory tendency. Our study reinforces the view that the migratory behavior is an evolutionary complex trait conditioned by the interaction of individual, social and environmental factors. Particularly in long-lived species with extended parental care, the inherited migration program may be shaped by mother-offspring and social transmission of migratory patterns.