The sacred ibis Threskiornis aethiopicus (Latham, 1790) in the lagoon of Venice (ne Italy): a ten-year (2010-2019) synthesis on the occurrence of an invasive species.
Almost unknown until 2010, the Sacred Ibis Threskiornis aethiopicus is nowadays commonly seen in the whole lagoon of Venice and its surroundings, with a yearly mean increase of about 50% in the number of observations reported by local ornithologists and birdwatchers. The species exploits several feeding habitats, such as agricultural fields, in particular ditches and small channels, tidal flats emerging during the low tides, saltmarsh ponds and creeks, edge of reedbeds, dredge islands and small ponds inside urban parks. The group size of foraging birds is often < 10, sometimes associated with Little Egret Egretta garzetta, White Egret Ardea alba and Grey Heron Ardea cinerea. The Sacred Ibis tolerates well the presence of people, as shown by a flight initiation distance of just 49.7 m (+ 26.7, N=35). Between 2010 and 2019, no predation by the Sacred Ibis of eggs/chicks in the many colonies of seabirds and waders monitored by the authors has been observed. Nesting of the Sacred Ibis in the study area has not been confirmed, despite being possible. A precise estimation of the Sacred Ibis population occurring in the lagoon of Venice is needed, while the enforcement of control/eradication measures must be soon evaluated.