The proposed project aims at understanding the mechanisms of mate choice in socially monogamous non-passerine bird with a low level of sexual dimorphism, the Grey Partridge Perdix perdix. The main goal is to evaluate the signalling function of male and female ornaments using both experimental and field approaches. The link among ornament expression, immunoresponsiveness, parasite load, survivorship and presence of various alleles of genes involved in immunity will be assessed. Description of MHC and other immunologically important segments of the genome (such as TLRs that will be described for the first time in wild living animal population) will fill a gap in our knowledge about the evolution of immune system in the Galliformes and enable us untangle the role that immunity genes play either directly or indirectly through ornament expression in mate choice decisions. Two basic alternative mechanisms of mate choice, based on presence of convenient alleles (‘good genes’) and/or genetic complementarity will be evaluated. Complex life-time data available for most individuals should provide estimates of the relative investments into ornaments and reproduction, changes in ornament expression over time as well as effect of parental immunity genes on offspring survival.