SOVON (1986) Cooperating Organizations Bird Research Netherlands. What does the counter?. LIMOSA 59 (1): 43-43.

BSP for the counter specifically looking for rare breeding colony and brother in a particular block (Table 1). The size of the area is 2.5 x 2.5 km2 (fourth atlas block). The counter visits the area regularly during the breeding season, both in Early morning and evening and night

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