Possible effects of nest predation on ground nest survival in the Neretva delta (Croatia)

Nest predation experiment to survey survival probabilities of larger bodied ground-nesting birds (ducks) was carried out on Lake Kuti in May 2006. From 25 artificial ground nests on the floating reedbed islands and 25 nests on the grazed islands, 8 and 1, respectively, were depredated. On the contrary to our expectations, the daily survival rate of artificial nest on the reedbed islands i.e. closed habitats was significantly lower (95.06%) than in the open habitat islands being grazed by sheep and cattle (99.43%). Broken chicken eggs and the marks left behind on plasticine eggs suggested that the predators were probably small mammals and birds. Such predators do not pose serious threat to real nests and clutches, thus they are unlikely to have had significant influence on the dramatic decrease of nesting bird populations in the area.