A growth cost of begging in captive canary chicks

Nestling birds solicit food from adults by using begging displays that appe ar paradoxically costly and wasteful. Theoretical work suggests that the ev olution of such exuberant offspring behavior reflects parent-offspring conf lict over the supply of parental investment. Originally, extravagant beggin g was seen as a means of psychological trickery by which offspring could wh eedle additional resources from resistant parents. Subsequently, costly beg ging came to be viewed as the hallmark of resolved parent-offspring conflic t, serving either to prevent escalated scramble competition or to enforce h onest signaling. However, the theoretical assumption of costly solicitation has been called into question by the low level of energy expenditure measu red empirically during begging. This finding has prompted new theoretical w ork that shows that begging can be cost-free and yet still resolve parent-o ffspring conflict. Here, I report that begging is more costly than recent w ork suggests. My experimental evidence from captive canaries demonstrates a marginal cost of begging through impaired growth. Furthermore, I argue tha t previous studies of energy expenditure during solicitation do not measure the cost of begging, as defined theoretically. More generally, my results may account for the evolution of nestling growth rates, as well as the obse rvation that begging is typically most flamboyant in older offspring.