title: Experimental manipulation of tail ornament size affects the hematocrit of male barn swallows (Hirundo rustica).
abstract: Ornamental tail feathers of male barn swallows (Hirundo rustica) confer an advantage in sexual selection because long-tailed males are preferred by females. However, the size of tail ornaments exceeds the natural selection optimum and males are predicted to pay an energetic cost for flying, directly related to tail length. An increase in hematocrit is an adaptive response to enhance oxygen uptake, for example during periods of intense locomotory activity. In this study, we analyzed the effect of experimental manipulation of tail length on the hematocrit of male barn swallows from an Italian and a Spanish population. We predicted that the natural decrease in hematocrit during the breeding season would be reduced by experimental elongation and enhanced by experimental shortening of tail ornaments. The results showed that the decrease in hematocrit was significantly different among tail treatments, and tail-elongated males had the smallest hematocrit reduction. In Italy, the hematocrit of tail-elongated males did not change after tail manipulation, while that of two control groups and tail-shortened males decreased. A comparatively high hematocrit in males with experimentally enlarged tail ornaments may be a response to increased energetic requirements and, hence, to oxygen demands for flying imposed by their tail morphology.
authors.affiliation: Dipartimento di Biologia, Sez. Zoologia Scienze Naturali, Via Celoria 26, I-20133 Milano, Italy fax: +39 2 2362726; e-mail: n.saino@imiucca.csi.unimi.it, , , , , , IT.
authors.forename: Nicola
authors.initials: N
authors.lastname: Saino
authors.affiliation: Laboratoire d'Ecologie, CNRS URA 258, Université Pierre et Marie Curie, 7 quai St. Bernard, Case 237, F-75252 Paris Cedex 05, France , , , , , , FR.
authors.forename: José Javier
authors.initials: JJ
authors.lastname: Cuervo
authors.affiliation: Dipartimento di Biologia, Sez. Zoologia Scienze Naturali, Via Celoria 26, I-20133 Milano, Italy fax: +39 2 2362726; e-mail: n.saino@imiucca.csi.unimi.it, , , , , , IT.
authors.forename: Marco
authors.initials: M
authors.lastname: Krivacek
authors.affiliation: Departamento de Biologia Animal, Universidad de Extremadura, E-06071 Badajoz, Spain, , , , , , ES.
authors.forename: Florentino
authors.initials: F
authors.lastname: de Lope
authors.affiliation: Laboratoire d'Ecologie, CNRS URA 258, Université Pierre et Marie Curie, 7 quai St. Bernard, Case 237, F-75252 Paris Cedex 05, France , , , , , , FR.
authors.forename: Anders Pape
authors.initials: AP
authors.lastname: Møller
keywords: Key words Hematocrit ;  Hirundo rustica ;  Secondary sexual characters