Is Carrying Feathers a Sexually Selected Trait in House Sparrows? Lola Garc  ıa-L opez de Hierro*, Marcos Mole on† & Peter G. Ryan‡ * Departamento de Zoolog  ıa, Facultad de Ciencias, Universidad de Granada, Granada, Spain † Centre for African Ecology, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa ‡ Percy FitzPatrick Institute, DST/NRF Centre of Excellence, University of Cape Town, Rondebosch, South Africa Correspondence Dr. Lola Garc  ıa-L opez de Hierro, Camino de Santa Fe ´ , 17, 18101, Belicena, Granada, Spain. E-mails: lolaglh@ugr.es; lolaglh@hotmail.com Received: July 2, 2012 Initial acceptance: August 26, 2012 Final acceptance: December 10, 2012 (T. Tregenza) doi: 10.1111/eth.12053 Abstract Males in several avian groups carry specialised materials as part of their courtship display. Females may vary their investment in reproduction in relation to their mates’ attractiveness. The house sparrow (Passer domesticus) population on Dassen Island, South Africa, builds domed nests in the branches of trees. These nests are more or less spherical structures with a deep cup lined largely with feathers. When males collect feathers, they call to females and display the feather before it is added to the nest. We exam- ined whether carrying feathers provides females with an index of male quality, which correlates with their subsequent investment in parental care. Additionally, we studied the potential importance of feathers in nest insula- tion. Feathers were collected mainly by males. Males also brought larger feathers, and deposited more feathers in nests, than females. Number of trips with feathers – which increased after feathers were experimentally removed from nests – and number of feathers brought varied among males. Volume of feathers influenced females’ investment in reproduction and positively correlated with clutch size and chick feeding rates. We found more feathers during incubation and immediately after chicks hatched, when nest heat requirements peak. Furthermore, number of trips with feathers and number and size of feathers were greater during incubation. Our results suggest that this feather-carrying behaviour by male house sparrows influences maternal reproduction investment and could be a kind of parental care per se by supplementing nest insulation. Introduction Sexual selection has been suggested to be a continu- ous process during different stages of the reproductive cycle, including both the pre-and post-mating periods (e.g. Thornhill 1983; Møller 1994; Eberhard 1996; Soler et al. 1998a,b). Whatever the stage is, the differ- ential allocation hypothesis (Burley 1988) predicts that those individuals able to allocate resources depending on their mates’ attributes (i.e. attractive- ness) should be favoured in the course of evolution, provided these mate traits are honest indicators of mate quality. Females may benefit from their choice either directly through enhanced parental care or territory defence by their mates (Trivers 1972; Kirkpatrick 1985; Price et al. 1993) or indirectly by acquiring ‘good genes’ for their offspring (i.e. male quality, Zahavi 1975; Pomiankowski 1987; Iwasa et al. 1991). At the post-mating stage, females can respond to their mate’s attractiveness by varying investment in reproduction (Thornhill 1983, 1984; Simmons 1987; Yamamoto et al. 1989; Petrie & Williams 1993). In many birds, female reproductive investment can be well measured through clutch size (Mousseau & Fox 1998) and feeding effort (see Sheldon 2000). In some bird species, the females that pair with more attractive males lay more eggs and increase the feeding rate than those paired with less attractive males (Petrie & Williams 1993; Schwabl et al. 1997; Sheldon 2000). Ethology 119 (2013) 199–211 © 2013 Blackwell Verlag GmbH 199 Ethology