Nest characteristics can significantly affect specific behaviour of predators during nest depredation, such as relating to nest searching, manipulating and eating eggs. However, the effect of egg size and coloration on behaviour of avian predators rarely has been quantified. Since the European Black-billed Magpie Pica pica is regarded as an important nest predator in suburban areas, we studied the effect of different types of artificial ground nests — baited with chicken and quail eggs — on predation probability by magpie. In addition, to compare temporal changes in magpie predation, experimental clutches were installed at 39 active magpie nests in two breeding stages: incubation stage and stage of nestling feeding. In our experiment, magpies detected almost all artificial nests at both breeding stages. However in contrast to our prediction, nests were preferentially depredated at the first stage. This probably was due to the change of magpie foraging preference to invertebrates as a main food of nestlings. Furthermore, we found that predation rate did not differ between real and wax eggs, suggesting that magpies are not able to discriminate between them. Whereas quail eggs were carried away, chicken eggs were consumed in the nest where remnants of egg shell and egg content were left. Obviously, the possibility to immediately carry the egg away increases food attractiveness for magpies. Therefore, we conclude that chicken eggs are more suitable for identification of middle-sized avian predators than quail eggs.
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