Quality, need, or hunger; begging the question

Why do birds and mammals beg and bleat in ways that are energetically wasteful and risk other fitness consequences such as attracting predators? Most workers assume that some genetic conflict is involved, either between parents and offspring or amongst siblings. Mock et al. (2011) provide a thoughtful analysis of the theories available concentrating on those that assume the parent actively chooses which young to feed and that begging and bleating are evolved signals. They argue that the field has concentrated too much on the signal being one of need rather than of quality and discuss a third alternative--signals of hunger. We offer here a few comments in support of Mock et al.'s sensible call for greater debate on alternative mechanisms, though argue that most available evidence supports begging as a signal of need. Copyright 2011, Oxford University Press.