Night Heron (Nycticorax nycticorax) - this species is exceptional for Czaplon. Upper Vistula Valley is the only pleace in Poland known as annual breeding site of this species. Night heron has bred here since XVI century. Until 80-ies this heron has bred in number about 50-70 pairs. From the beginning our studies we exactly monitor its number, and during last 6 years we have noted significal raise of the breeding population number. In 1999 members of Czaplon group found 319 nest located in 7 colonies.