Blackbird (Turdus merula) Science Article 3
An urban Blackbird Turdus merula population was studied in Budapest from 1986 to 1989. Seasonal pattern of breeding success was similar in three out of the four years: early nests were successful then the success rapidly fell, reaching another maximum in the third part of the breeding season, and finally became low again. Besides breeding success the proportion of broad-leaved trees and the average height of nests changed during the season. Nest-height seemed to have a greater effect on the seasonal pattern of breeding success than the type of trees. In case of low nests (h > = 2 m) the seasonal pattern of hatching success was due to desertion as well as predation. In the medium nests (2m < h < = 3 m) the main cause of the seasonal pattern of hatching success was desertion, while it was predation in case of high nests (h > 3 m). The seasonal pattern of fledging success was caused by predation in all three height-categories, as parents rarely desert nestlings. Because more nests failed during the incubation than the nestling period, the seasonal pattern of breeding success was caused mainly by the factor that shaped the pattern of hatching success in all height-categories.
Ludvig E., Vanicsek L., Torok J. & Csorgo T., ARDEA 83 (2): 411-418.