Use of artificial intertidal sites by birds in a Mediterranean lagoon and their importance for wintering and migrating waders

Abstract

Man-made habitats provide suitable nesting, resting and feeding habitats for many birds at coastal sites. Despite intensive study outside Europe, very few data are available to date on the bird communities that exploit artificial intertidal sites along the European coasts. Between July 2009 and December 2010, 32 ornithological surveys were performed at six artificial intertidal sites in the lagoon of Venice (Italy). Overall, 101 species (with 23,399 birds) were observed, about a third of those occurring in the lagoon of Venice; 58 of these species were of conservation concern. Ten species comprised about 80 % of the total; bird abundance was the highest during the post-breeding migration and wintering period. Multivariate analysis identified similarity among sites, seasons and observed behaviours. Dredge islands were mostly used by waders as foraging sites, when surrounding tidal flats were still flooded. In winter the six dredged islands supported about 2 % of the dunlins Calidris alpina occurring in the whole lagoon of Venice and about 10 % of the grey plovers Pluvialis squatarola. Since the study sites comprised just the 6 % of the total dredge island area available in 2009–2010, the results indicate as large fractions of these shorebird populations might exploit the dredge island habitats for foraging. Among the newly created habitats, intertidal ponds and inner tidal flats were the most heavily used by birds, followed by dykes and mounds with ruderal vegetation. Maintenance of the habitat mosaic is a need for a conservation- based management of the dredge islands.