Gli uccelli acquatici svernanti nella laguna di Venezia nel periodo 1993-2007: analisi delle dinamiche temporali e spaziali

Scarton F., Bon M.

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Waterbirds wintering in the lagoon of Venice (Italy), 1993 - 2007, trends and spatial distribution. The waterbirds wintering in the lagoon of Venice increased from 74,462 birds (1993) to 201,717 (2007), counted during mean winter counts that encompassed the whole lagoon (about 55,000 ha in surface area). The peak value was attained in 2005 (214,640 birds), and the 2003-2007 mean was 195,672 birds, which makes the lagoon of Venice the most important wintering area in Italy and one of the most important in the whole Mediterranean. Ducks were the majority, recently 53% of the total waterbirds; gulls (17%), waders (14%) and coots (13%) were the other most important groups. Over the last fve years, about 80% of the birds were counted inside fsh farms, which span over 9,500 ha, and 20% in the open lagoon, with negligible percentages along the littoral strip. Inside fsh farms, where hunting occurs, density as high as 48 birds/ha was reached during daytime. Over the whole lagoon, waders reached a density of 4.5 birds/ha of tidal flats (dunlin 3.8/ha; curlew 0.3/ha; avocet 0.2/ha). From 1993 to 2007 and also from 1998 to 2007, most species showed stable or increasing trends, with only eight species, grebes and Red-breasted Merganser in particular, decreasing. Ducks showed a spectacular increase, with more than 100,000 birds gained in 15 years; most of these were Teals (+ 44,433 birds) and Mallards (+ 38,492 birds). Similar trends, even if less pronounced, were observed for three other northern Adriatic wetlands. On the other hand, in the rest of the Mediterranean many species did not show trends comparable to those observed in the Venice lagoon.