title: Energetic cost of tail streamers in the barn swallow (Hirundo rustica).
abstract: Different hypotheses stress the importance of natural or sexual selection to explain the evolution and maintenance of long outermost tail feathers in the barn swallow (Hirundo rustica). Since energy costs are predicted to arise from tail length manipulation, we measured the daily energy expenditure in three experimental groups (tail-shortened, tail-elongated, and control birds) with the doubly labelled water technique. Though we did not directly measure flight cost, we assumed this to be positively related to daily energy expenditure. Mass independent daily energy expenditure (kJ/mass0.67day) average daily metabolic rate (ml CO2/g h), and water flux (ml H2O/g day) did not show any significant difference among treatments in either sex. Males had higher values than females for the three parameters. Males with short original tail length experienced a higher water flux than originally long-tailed males. Females that laid more eggs during the breeding season or had heavier broods also showed higher levels of water flux which could imply a higher food intake. Our expectation of finding energetic costs of manipulated tail length in barn swallows with an integrated measure of metabolism was not fulfilled, and we did not find evidence for behavioural changes in the birds involved in the experiment.
authors.affiliation: Department of Population Biology, Zoological Institute, Copenhagen University, Universitetsparken 15, DK-2100, Copenhagen Ø, Denmark.
authors.forename: José Javier
authors.initials: JJ
authors.lastname: Cuervo
authors.affiliation: Departamento de Ciencias Morfológicas y Biología Celular y Animal, Facultad de Ciencias, Universidad de Extremadura, E-06071, Badajoz, Spain.
authors.forename: Florentino
authors.initials: F
authors.lastname: de Lope
authors.affiliation: Department of Population Biology, Zoological Institute, Copenhagen University, Universitetsparken 15, DK-2100, Copenhagen Ø, Denmark.
authors.forename: Anders Pape
authors.initials: AP
authors.lastname: Møller
authors.affiliation: Museo Nacional de Ciencias Naturales, José Gutiérrez Abascal 2, E-28006, Madrid, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Moreno
keywords: Doubly labelled water; Energy expenditure; Metabolism; Sexual selection; Tail ornament