Bean goose migration shows a long-term temporal shift to earlier spring, but not to later autumn migration in Finland

Climate change can challenge the inherited or learned behavioural patterns that were useful in the past. In particular, it may change the spatio-temporal dynamics of migratory behaviour in birds. Here, we explored a 40-year-long time series of Bean Goose (Anser fabalis) observations using a citizen science database (tiira.fi – BirdLife Finland) to link the timing of the migration across last forty years and with the large-scale temporal weather fluctuation described by an index of North Atlantic Oscillation (NAO). During 1978–2018, the peak of spring migration of the Bean Goose has advanced approximately a month, whereas the timing of autumn migration has remained more similar across the years. The NAO index was associated only with spring migration. Strong temporal changes of the Bean Goose migration are evident as they adjust their migratory behaviour to changing spring conditions.