Reproductive performance of white storks Ciconia ciconia breeding at low and high densities

Reproductive performance, parental activity and body mass of parents were recorded for white storks Ciconia ciconia L. breeding at high density (the town of Kormend, West-Hungary) or at low density (Kiskunsag National Park, Central-Hungary). Three categories of nest use were distinguished: (1) those abandoned for at least a year before they were re-occupied during the study period (1991-1997), (2) those occupied throughout the study period and (3) those abandoned after having been used for at least one year of the study period. Late egg-laying, low parental body mass at the start of incubation, small clutch size, low mass of food delivered to the chicks, high chick mortality and few fledglings raised were all associated with nest type 1. Early egg-laying, high parental body mass, large clutch size, high mass of food delivered to the chicks, low chick mortality and many fledglings raised were all associated with nest category 2. These contrasting values support our suggestion that younger birds bred in nest category 1, whereas older parents occupied nest type 2. The proportion of nests occupied by presumed young parents was higher in the high density than in the low density population. The chicks fledged from small broods were heavier than those from large broods and, as a consequence of the higher proportion of young parents producing such small broods, the mean body mass of offspring raised in nests in high breeding density was higher than for those from low density.