Effect of parental care on depredation of Blackcap Sylvia atricapilla L. nests: an experiment with artificial clutches

Small solitary open nesting passerines, such is the Blackcap Sylvia atricapilla that builds nest in the undergrowth, have little chance of successfully scaring off a predator to defend a nest. The aim of our study was to determine if parental care by Blackcaps can reduce the risk of depredation of its nests. We compared the survival of natural clutches with artificial clutches (plasticine and independently both plasticine & quail eggs). The artificial clutch was placed in a nest after the natural clutch had been concluded, and the results were analysed as matched pairs of data. We assumed that significantly higher survival rates of natural clutches than of artificial clutches deprived of parental care, might indicate a significant positive effect of parental care on reducing depredation risk of Blackcap clutches. Losses caused by birds, rodents and larger mammals were 49%, 41% and 9%, respectively. The differences in survival rates of artificial clutches (plasticine as well as quail & plasticine) and natural clutches were not statistically significant. This might show that parental care is not strong enough to significantly reduce depredation risk of Blackcap clutches. Although this conclusion should be treated cautiously because it was difficult to assess the influence of using artificial clutches on our results.