Nest dispersion, diet, and breeding success of Black Kites (Milvus migrans) in the Italian pre-Alps

We studied a population of Black Kites (Milvus migrans) from 1992-96 in a 1 00-km(2) study area in the Italian pre-Alps around Lake Lugano. Population density increased from 24 territorial pairs per 100 km(2) in 1992 to 38 in 1996. Nearest neighbor distances were variable, averaging 1288 m for solita ry pairs (N = 24) and 306 m for colonial ones (N = 151). Regular spacing of nest sites was the rule within colonies, but inter-nest distance for solit ary breeders increased as new pairs settled in the area. Nests occurred bot h in trees (58%, N = 84) and on cliffs (42%); 23% and 5% (N = 84) of the ne sts were originally built by Common Buzzards (Buteo buteo) and Ravens (Corv us corax), respectively Mean laying date was 25 April (N = 42), mean clutch size was 2.29 eggs (N = 42) and mean number of fledged young was 0.97, 1.1 1, and 1.78 young per territorial, reproductive, and successful pairs, resp ectively (N = 143, 95, 78). The percentage of successful territorial pairs was 55% (N = 143). Diet was dominated by fish and birds, which accounted fo r 62% and 28% of 307 identified prey items, respectively Compared with othe r European populations, this population showed an intermediate density and an average clutch size but the lowest fledging and breeding success ever re corded for the species. Reasons for the low success were unclear, but may h ave been related to low food availability or water pollution and consequent pesticide contamination.