Nest predation and the evolution of nestling begging calls

Begging by nestling birds can be conspicuous and loud. Such displays are th ought to function in signalling nestling condition and securing parental ca re, but they also may inadvertently attract the attention of predators. We compared the structure of nestling begging calls to the risk of predation a mong 24 species of birds breeding in a forest community in central Arizona. After controlling for body size and phylogeny, we found that species subje ct to greater nest predation had calls with higher frequency (pitch) and lo wer amplitude (loudness) than species subject to lower rates of nest predat ion. As these acoustic features make it difficult for potential predators t o pinpoint the source: of a sound, our results suggest that an increased ri sk of predation has led to the evolution of begging calls that minimize loc atability. The relationship between call structure and the risk of predatio n also supports the hypothesis that attracting predators is a direct cost o f begging and that such costs can constrain any evolutionary escalation in the intensity of nestling begging.