Some comparative aspects of the breeding biology of Black-headed Gull (Larus ridibundus), Common Tern (Sterna hirundo) and LittleTern (Sterna albifrons) in the Lagoon of Venice, NE Italy


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During the years 1989-1992 three species of Laridae and Sternidae breeding in the lagoon of Venice were studied. The breeding population of L. ridibundus increased steadily through the period of study, whereas S. hirundo was stable and S. albifrons decreased. Alrnost ali of the colonies were closely clustered in the southern lagoon, where hurnan disturbance is less heavy. Colonies were located on a few of the apparently favourable sites. Colony size was significantly higher in S. hirundo (90.8 ± 80.1, n=45) than in S. albifrons (51.9 ± 72.3, n= 12) and in L. ridibundus (26.3 ± 42.5, n=20). S. hirundo was significantly associated with L. ridibundus, whereas S. albifrons avoided the occurrence ofthe latter species. Site tenacity did not differ arnong species, with the rnajority of sites being occupied only for one or two years. Suggestions for the protection ofthe colonies are proposed.