Male rock sparrows differentially allocate nest defence but not food provisioning to offspring Giuliano Matessi 1,3) , Cristina Carmagnani 2) , Matteo Griggio 2) & Andrea Pilastro 2) ( 1 Animal Behaviour Group, Department of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen Ø., Denmark; 2 Department of Biology, University of Padova, Padova, Italy) (Accepted: 13 June 2008) Summary Secondary sexual characters may provide information about individual quality to a partner, which may use it during parental care to strategically allocate resources to the current breed- ing attempt (Differential Allocation Hypothesis). Differential allocation by females has been demonstrated for a number of species, while male differential allocation based on female secondary sexual traits has received less attention. Yet females of many species, among birds in particular, are ornamented. We performed a test of male differential allocation based on a female ornament in the rock sparrow (Petronia petronia), a monomorphic species in which both sexes have a yellow breast patch, the size of which correlates with individual reproduc- tive quality. We reduced the breast patch in a sample of females and compared the parental care of their partners (chick feeding and nest defence) with the parental care of males paired to sham-manipulated controls. Nest defence was assessed by placing a dummy predator on the nest box. Males of ornament-reduced females defended the nest less but did not feed the chicks less than males paired to control females. Our results only partially support male dif- ferential allocation and are in agreement with previous tests of male differential allocation in rock sparrows. Keywords: differential allocation hypothesis, parental care, male parental investment, female ornaments, nest defence. 3) Corresponding author’s e-mail address: gmatessi@bio.ku.dk © Koninklijke Brill NV, Leiden, 2009 Behaviour 146, 209-223 DOI:10.1163/156853909X410748 Also available online - www.brill.nl/beh