Nest building is a sexually selected behaviour in the barn swallow

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JUAN JOSEu SOLER*, JOSEu JAVIER CUERVO†, ANDERS PAPE MØLLER‡ & FLORENTINO DE LOPE§ *Departamento de Biologi ́a Animal y Ecologi ́a, Universidad de Granada †Estacio ́ n Biolo ́ gica de Don ̃ana, C.S.I.C. ‡Laboratoire d’Ecologie, CNRS URA 258, Universite ́ Pierre et Marie Curie §Departamento de Zoologi ́a, Universidad de Extremadura (Received 19 March 1998; initial acceptance 28 April 1998; final acceptance 16 June 1998; MS. number: 5827)
ABSTRACT Females may use male nest building to assess male parental quality, and nest size would then be a sexually selected trait. In the barn swallow, Hirundo rustica, females select their partner by his tail length, a character believed to signal good genes. Both sexes participate in nest building, although male participation is negatively related to his attractiveness as reflected by tail length. We tested the hypothesis that nest building is a sexually selected trait: females paired with males of high parental quality (as shown by the male during nest building) may obtain a mate providing large amounts of parental investment, while, as has been shown previously, females mated to attractive (long-tailed) males will acquire mates with good genetic quality. Therefore, since nest building in barn swallows occurs after mating, we predicted a postmating sexual selection process by which the female invests differentially in reproduction depending on the male’s nest-building effort (reflecting his willingness to invest in reproduction). The volume of material in a nest was related to the male’s contribution to nest building and, in agreement with our hypothesis, in a multiple regression analysis, male tail length and nest material volume were negatively related to laying date and positively to female investment in reproduction (total number of eggs laid during the breeding season). Moreover, females paired with long-tailed males (which contribute very little to nest building), but using the same amount of nest material as females paired with short-tailed males, reduced the thickness of the nest and hence increased its capacity. Therefore, in the barn swallow two different traits appear to be sexually selected: tail length of males owing to the good genes process and nest-building ability owing to the good parent process.  1998 The Association for the Study of Animal Behaviour
Nest-building behaviour is often associated with courtship and pair formation in birds. The degree to which this behaviour is used in courtship varies from mere manipulation of a piece of nest material or display of a potential nest site to the building of an entire nest by the male (Collias & Collias 1984). Nest-building behaviour is also used in sexual display by both polygynous and monogamous bird species (see examples in Collias & Collias 1984) in a postmating sexual selection process (Møller et al. 1995). Nest-building behaviour may signal the reproductive condition of individuals and physiologically stimulate a partner (Collias 1964), but there is very little information on the importance of the nest itself and its role in mate choice (Hoi et al. 1994). The nest may indicate parental quality, experience or genetic quality, and females could therefore benefit from mating with a superior nest builder. Nest-building behaviour could provide information to pair members about the quality of the potential partner, and such assessment of mate quality may allow individuals to choose a mate in nonmonogamous species, while in monogamous species assessment may also allow partners to invest differentially in reproduction relative to the quality of the mate (Burley 1986; Møller 1994). In a comparative study of nest size in relation to parental effort in birds, Soler et al. (1998) showed that bird species in which both sexes build the nest have larger nests than those in which only the female builds. Nest size (relative to body size) was positively correlated with Correspondence: J. J. Soler, Departamento de Biologi ́a Animal y Ecologi ́a, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain (email: jsolerc@goliat.ugr.es). J. J. Cuervo is at the Estacio ́n Biologica de Don ̃ana, C.S.I.C., Apartado 1056, E-41080 Sevilla, Spain. A. P. Møller is at the Laboratoire d’Ecologie, CNRS URA 258, Universite ́ Pierre et Marie Curie, Baˆtiment A, 7e ́me e ́tage, 7 quai St Bernard, Case 237, F-75252 Paris cedex 05, France. F. de Lope is at the Departamento de Zoologi ́a, Facultad de Ciencias, Universidad de Extremadura, E-06071 Badajoz, Spain. 0003–3472/98/121435+08 $30.00/0  1998 The Association for the Study of Animal Behaviour1435