La popolazione di  Larus cachinnans michahellis nidificante nella città di Trieste.

BENUSSI E., FLAPP F. e MANGANI U.

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Abstract:

Urban nesting by Yellow-Legged Herring Gulls in the city ofTrieste was first observed in 1987. The number of nests on the top of buildings increased by 49.9% on average each year since 1988, this increase may dictate management measures in the future. A specific research was carri ed out in 1992 in order to investigate the relations between environmental factors and distribution, and the breeding succes. A total population of 70-90 breeding pairs was estimated both by direct nest counts (66 breeding pairs) and by contemporary counts on the calling adults. A colony (24 nests) was located in the industriaI harbour area, while the nests in the urban area (37) can be described as a loose colony. Breeding site features such as exposure and roof covering, distance from sea and from nearest nest were surveyed and their distribution and effect on breeding were analyzed. Hatching and survival ratio and breeding success were significantly higher in the urban area than in the industriaI area colony.