Blackcap Sylvia atricapilla nestlings do not produce begging calls until they are able to escape from predators

Abstract

Nest predation is a major source of reproductive failure in birds and thus it can exert selection on both parental and offspring strategies. Begging calls are known to be a powerful component of parent–offspring communication but these calls can also increase predation risk. Here we demonstrate a sophisticated strategy for the development of begging vocalization in a species under high nest predation. Blackcap Sylvia atricapilla nestlings spend most of their nesting period silent, and develop begging calls just before they are able to fledge. The onset of begging vocalization matches the onset of endothermy, which enables Blackcap chicks to leave the nest. We demonstrate experimentally that begging calls function as a signal of the increased needs of homeothermic nestlings. Playback of begging calls conducted in nests with silent nestlings resulted in a significant increase in feeding rates and a decrease in brooding. Development of begging calls only at the age of endothermy allows species under high nest predation to keep the risky period of begging vocalizations and frequent feeding to a minimum. This strategy may constitute an evolutionary solution to high predation pressure in some open nesting passerines. This is the first study to demonstrate the existence of silent begging in a passerine.