Knowledge on flyway structures, year-round spatiotemporal distributions and migration strategies is a key for understanding the ecology of migratory populations and the evolution of migratory behaviours. Knowledge on these factors is also a prerequisite to reliably estimate the size and trend of migratory populations, and to successfully conserve and manage them.

In this thesis, I studied the migratory behaviour of two goose species, the bean goose (Anser fabalis) and the greylag goose (Anser anser) using high-resolution satellite tracking, traditional neckbanding and birdwatcher observations. Satellite tracked taiga bean geese belonging to the Central Flyway population revealed a comprehensive moult migration of non-breeding and unsuccessfully breeding birds to the Arctic. This behaviour increases the length of the annual migration distance and delays the autumn migration of moult migrants. The strength of migratory connectivity among the population was moderate to low between breeding and nonbreeding areas, and both migratory connectivity and the spatial distribution of the population varied substantially within the non-breeding season. Additionally, satellite tracking indicated that the current population censuses might underestimate the size of the taiga bean goose population. Birdwatcher observations showed both spatial and temporal difference in occurrence of different bean goose subspecies in Finland during spring and autumn migrations, which affects the harvest management of the subspecies with different conservation statuses.

The satellite tracking data and neckband resightings of greylag geese confirmed the existence of a gradual migratory divide in the continuous breeding distribution of the species. The birds breeding at the different ends of the greylag goose breeding distribution in Finland used different flyways (Western and Central), and the birds breeding between these two extremes scattered to the two flyways. The migration strategies differed between the flyways. The overall migratory journey is longer for birds using the Western Flyway, and these birds migrate earlier in autumn and later in spring than birds on the Central Flyway. Birds using the Western Flyway also show a clear stopover of around one month during their autumn migration, whereas Central Flyway birds migrate relatively straight from their breeding grounds to their wintering sites.

The results of the thesis help to delineate the flyways of both species, provide aspects needed to understand their ecology, and supports the ongoing international management of the species. Furthermore, the results build possibilities to further study not only these two species, but also more general ecological questions related to bird migration and movement ecology.