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Résumé :
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Mediterranean Gulls Ichthyaetus melanocephalus usually position their nests close to water, just above the high-water mark, and are thus vulnerable to flooding caused by extreme water levels and tidal surges at coastal locations. This short paper describes long-term productivity and causes of failure in relation to habitat choice of Mediterranean Gulls during their colonisation of the Venice Lagoon, northeast Italy, in the last decade. During the study period, huge colonies of nesting Mediterranean Gulls have occurred in the area in some years, while there have been no nesting pairs at all in others. Overall, we found nine colonies at three sites in seven different years. The mean colony size was 618 (±926) pairs (range 1–2,512). Most colonies (7 out of 9, 78%) were found on marshy islands, while two were found on artificial islands. Overall fledging success was low, with 650 chicks fledged from 4,329 nests during the ten-year study period, which corresponded to 0.15 fledglings per nesting attempt. This was due to catastrophic failures, caused by extreme high tides flooding most nests/clutches. Our work provides evidence of the risks that waterbirds nesting on saltmarshes are facing due to unprecedented increases in sea-levels and extreme weather events, and shows that these are leading to serious declines in reproductive success in consecutive breeding seasons.
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