Migratory behavior is found in numerous species from all parts of the world. The sum of individual migration behavior forms the characteristics of population migration patterns, which may have high impact on ecosystem dynamics. Individual migration behavior may be driven by external factors, such as temperature or food availability or by internal factors such as genetic programming or experience. The latter may lead to a bivariate life history pattern, i.e. alternative behavioral strategies. Whereas this has been found in a number of animals, few studies has been able to study the consistency of alternative migration strategies, which is most likely due to the logistical difficulty of determining individual migration patterns accurately for a large number of individuals. However, in cyprinid fish winter migrations from lakes into streams, fish have a very narrow migration route compared to terrestrial animals, which provides an opportunity for detecting and timing individual migration with high accuracy. By marking many individuals with uniquely coded electronic tags and recording their movement for six consecutive years we were able to get highly detailed information on individual consistency in migration patterns.
We found that individual fish was more likely to migrate in subsequent years if they had migrated before, that individual fish were more likely to choose the same stream as they had chosen in previous years and that the individual timing of migration one year was correlated with the timing of migration the next year. Collectively these results demonstrate high individual consistency in migration behavior, which is likely to de-couple environmental effects on migration. Since migration leads to relaxed trophic interaction between migrant predator and resident prey, in this case zooplankton, this decoupling may affect ecosystem dynamics and stability.