During migration in late autumn there are also numerous loons on the lake (black-throated and red-throated loon, as well as a few great northern loons). Lake Constance is also very important as a staging post during the bird migration. Bird migration is often inconspicuous and most noticeable when there are special weather conditions that make day migration obvious. Only where there is a prolonged spell of widespread low-pressure is it common to observe the congestion of large groups of migratory birds. This can often be observed in autumn on the Eriskircher Ried on the northern shore of Lake Constance. This is where broad front migration converges on the lake and birds then try to move along the shore towards the northwest. The importance of Lake Constance as an important area for resting and overwintering is underlined by the Max Planck Institute for Ornithology's Radolfzell Bird Observatory ("Vogelwarte Radolfzell"), which is the bird ringing centre for the German states of Bavaria, Baden-Württemberg, Berlin, Rhineland-Palatinate and the Saarland as well as for Austria, and which researches bird migration.