To boldly go: Animal personality and migration

Roach, a common cyprinid fish (photo: Jakob Brodersen)

Until quite recently personality was considered to be a uniquely human characteristic. Yet many studies now show that individual behavioural variation analogous to personality can be found in a diverse range of other animals, from birds to fish to ants. Animal personality has been linked to many important ecological processes involving movement, such as dispersal, but few studies have studied how personality traits can influence migratory behaviour in animals.

In a study recently published in Ecology Letters (see here), we investigated whether a common personality trait - boldness (an individual’s propensity to take risks) – influences the migratory behaviour of a widespread fish, the roach. Roach show an interesting form of migratory behaviour known as partial migration, which means that only a fraction of the population migrates out of shallow lakes overwinter into the connecting streams, and the rest remain resident the whole year around in the lake. We caught 460 fish prior to migration in two consecutive years and first quantified their risk-taking behaviour, and then followed their migratory behaviour using passive telemetry. We found that in both years individual boldness influenced migratory tendency in roach, with bold fish being more likely to migrate than shy fish. This data suggests that an extremely widespread personality trait in animals can have important ecological consequences via influencing individual-level migratory behaviour.

Why bold fish are more likely to migrate is an interesting question. One idea is that bold fish are more at risk of predation, and so when the food resources are low in the winter they migrate to refuge in the streams where predators are scarce, and only return to the lake when food availability increases in the spring. Another hypothesis is that bold fish are also more exploratory, and more likely to undertake the risky migratory journey into potentially new and unusual habitats when the benefits of living in the lake decline over winter. Work is underway to test some of these ideas, so watch this space!

/Ben