The date of the first observation of regionally common migratory birds within the Grimsö Wildlife Research Area (GWRA) has been recorded annually since 1985. Species observations (visual and/or auditory) are noted on a central list by any staff member. Observations are not made during a dedicated survey but can be made during field work, commuting, free time etc., but must occur within GWRA. The survey runs continuously, but data is compiled yearly.