DEPENDENCE OF CHICK KILLING ON NEST DENSITY IN A COLONY OF YELLOW-LEGGED GULL (LARUS CACHINNANS MICHAELLIS)

A study is reported of a yellow-legged gull (Larus cachinnans michaell is) colony located on a flat island in the lagoon of Venice, Italy. Ne sts and dead chicks, presumably killed by non parental adults, have be en recorded and mapped in the same area in three different years. A de nsity index, obtained by summing the squared reciprocals of the distan ces of each nest from all the others was used, to show the heterogenei ty of nest distribution in the colony. By subdividing the colony into quadrats of a size (10 000 m(2)) that maximizes the variation in avera ge nest number per quadrat, it is seen that the number of killed chick s/nests/quadrat increases with local nest density.