cause important losses to the biodiversity of small islands. In this study we
analysed the predation pressure on clutches of nesting birds in two islands of
the Zadar Archipelago, Olib and Silba, which belong to an Important Bird Area (IBA)
in Croatia. We paid special
attention to introduced mammals: black rats Rattus rattus and feral
domestic cats Felis silvestris catus. In May
2009, we carried out a study
with artificial ground and bush nests. One quail egg
and a plasticine egg of similar size were placed in each nest. On Olib, the
daily survival rate of quail eggs in ground nests (0.92) was similar to that of
nests located in shrubs (0.93), whereas on Silba the daily survival rates of
quail eggs in ground (0.94) and shrub nests (0.86) were significantly
different. We used the marks left on the plasticine eggs to identify nest predators.
Many eggs in shrub nests (40% on Olib and 70% on Silba) were predated by hooded
crows Corvus cornix. In ground nests on Olib, 43% of eggs were predated by hooded crows
and small mammals, mainly black rats. On Silba Island, eggs in 33% of the
ground nests were damaged by the above predators and also by the Montpellier
snake Malpolon monspessulanus.
Contrary to our expectations, feral cats were not found to be egg predators on
either of the islands.
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