Foraging Cost of Ornaments Which Are Not Ornaments: Comment on Matyjasiak et al. (1999)

In a recent article Matyjasiak et al[ "0888# tested the hypothesis that the cost of a long forked tail ornament can be due to impaired foraging[ The authors lengthened\ experimentally\ the outermost tail feathers of female sand martins "Riparia riparia# and checked the ~ight cost of the manipulation in terms of foraging cost\ i[e[ feeding rates and prey items size[ They found that tail!elongated females decreased the rate at which they fed nestlings\ and that they captured more but smaller insects[ These results would indicate the foraging cost of a tail ornament in the sand martin and would be consistent with the expectations of the handicap model of sexual selection[ Similar experiments by Mo ller and collaborators in the barn swallow "Hirundo rustica# have shown that experimental elongation of tail length in males has a detrimental e}ect on feeding rates and insect prey quality "Mo ller 0878^ de Lope + Mo ller 0882^ Mo ller + de Lope 0883^ Mo ller et al[ 0884#[ The authors argue that the results of the barn swallow studies might be biased because the apparent detrimental e}ect of elongated tails in males could be due to a decrease in male parental e}ort in response to an increase in female parental e}ort[ Female change in behaviour might be a consequence of increased male attractiveness "di}erential allocation of female parental e}ort^ Burley 0875#[ Matyjasiak et al[ "0888# solved this problem\ because female sand martins do not increase their attractiveness by possessing longer tail feathers[ First of all\ I agree that the results from the barn swallow experiments were not confounded by the di}erential allocation of female parental e}ort[ Mo ller and collaborators did not assess foraging costs of tail length manipulation in terms of male feeding rates\ but exclusively by measuring the size of prey items[ "Mo ller 0878^ Mo ller + de Lope 0883^ Mo ller et al[ 0884#[ In de Lope + Mo ller "0882#