F. Sergio et A. Boto, Nest dispersion, diet, and breeding success of Black Kites (Milvus migrans) in the Italian pre-Alps, J RAPT RES, 33(3), 1999, pp. 207-217
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.