Saaremaa is the biggest island of Estonia. Despite its comparatively small area (together with Muhu island - 2905 km2 ), the local avifauna is remarkably rich. Altogether 204 species of birds have been registered as nesting here, which constitutes about 90 per cent of all breeding bird species in Estonia. Together with transit migrants and occasional visitors, Saaremaa's bird list is as long as 300 species, which again  constitutes about 90 % of Estonian bird list. The main reason for such richness lies in the high diversity of Saaremaa's habitats.