Experimental evidence for a predation cost of begging using active nests and real chicks

The existence of begging costs has recently been the focus of evolutionary studies on parent-offspring conflict. Indirect findings seem to support the existence of a nest predation cost of begging. However, empirical direct evidence of nestling begging attracting the attention of nest predators has been criticized because of methodological problems, mainly the use of artificial nests and playbacks. In order to avoid this problem, we used natural and active nests and real chicks. We utilized Common Blackbird (Turdus merula) nests to experimentally create high and control begging nests by introducing a Great Spotted Cuckoo (Clamator glandarius) or Blackbird chick respectively. We also explored the effect of brood size comparing between Blackbird broods augmented and reduced by one chick. Experimentally parasitized nests were significantly more predated than simply augmented or reduced broods: nest predation for Cuckoo introduced (high begging) nests was more than double that predation for nests of the other two groups. However, we did not find any effect of the brood size. The presence of a Great Spotted Cuckoo chick in a nest also favors an earlier detection of the nest by predators. Parental activity at the nests seems not to be a factor explaining these results as we did not detect significant differences between Cuckoo and Blackbird introduced nests in visit rates. Therefore, our findings support the hypothesis that nestling begging has a severe cost in terms of predation and, hence, this cost may impose an important restriction to the evolution of begging behavior.