Bocian bialy (Ciconia ciconia) na Ziemi Łowickiej

Abstract

Having analysed materials collected in the Łowicz District in 1968 1970, 1974, 1975, 1983 and 1984 the author proved the occurrence of a continuous increase in the number of nests which were not occupied by pairs and nests which had no breeding success. Since 1970 the total number of nestlings which left their nests has also been on the decrease. Between 1970 and 1975 the density of pairs calculated for 100 km2 increased from 11.37 to 14.00 and then decreased to 10.39 in 1984. Positive changes in density were preceded by a high efficiency of breeding, while negative ones by a low efficiency. Since 1970 an increase in the number of nests built on the poles of electric traction has been observed. The author has proved that in places where groupings of nests (HP) consisted of more than 5 ones and when the distances between nearest ones did not exceed 1.5 km, intraspecific competition was the most significant factor limiting the efficiency of breeding.