BALEN JH & SPEEK BJ (1976) An irruption of Tits Paridae in the autumn of 1971. LIMOSA 49 (3): 188-200.

Great Tit Parus major Blue Tit Cyanistes caeruleus Coal Tit Periparus ater In the autumn of 1971 a large irruption of tits was observed in the Netherlands, Great Tit, Blue Tit and Coal Tit being the main participants. The irruption started in the last week of September, and continued into November (Fig. I). Blue Tits predominated during the first two weeks, Great Tits afterwards. From observations, ringing data (Fig. 2) and recovery localities (Fig. 3) it appeared that the largest numbers occurred in the northwestern and the central part of the country. From the ringing localities of foreign tits recovered in the Netherlands the origin of the irruption can be determined (Fig. 4 and 5). The are.a of origin is mainly the Baltic Sovjet Republics, Northern Poland and Northern Germany. Scandinavian tits were unlikely to have participated. Data from the literature and from letters from foreign ornithologists generally corresponded with the picture described above. Probably the Baltic tits arrived earlier than the German tits. The caJculated standard direction of the German tits was about West, that of German tits migrating to Belgium about WSW. The calculated speed of migration of the Baltic tits was about 40 km/day (varying from 34,4 to 52,4), which means that the journey took 3-5 weeks. Many of the immigrating tits must have spent the winter in the Netherlands, some of them travelled further to Belgium or Great Britain. There is evidence of spring migration through the Netherlands, and of migration towards the breeding area by tits wintering here. Tits of the Dutch breeding populations tended to show more movements in autumn than in most other years (Table 4). This corresponds with the high breeding population and the poor crop of beech mast in 1971

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