BRINK H VAN DEN (1993) Dutch Ornithological Union: National SOVON contact day, and Vogelbeschermin NOU: The meaning of Groningen for breeding birds and changes in the breeding population of Groningen. LIMOSA 66 (3): 128-129.

Dutch Ornithological Union: National SOVON contact day, and Vogelbeschermin NOU: The meaning of Groningen for breeding birds and changes in the breeding population of Groningen

[free pdf] [dutch summary]