Female promiscuity can function to acquire both direct and indirect benefits from their social mate and extra-pair males. In many raptor species, intense mate-feeding significantly contributes to female energy requirements before and during egg laying. Moreover, females may use mate-feeding effort to assess male quality. In this study of the lesser kestrel (Falco naumanni), we aimed at experimentally manipulating the female’s perception of mate quality by providing females with extra food during egg laying, and evaluated the occurrence of extra-pair paternity in food-supplemented and control broods by parentage analyses. No extra-pair offspring (EPO) was found among 19 food-supplemented broods, whereas EPO occurred in five out of 17 control broods. No significant differences in morphological traits, body condition and reproductive success were found between faithful and unfaithful females. However, clutches containing EPO were laid later in the breeding season. Moreover, un-cuckolded males had longer tarsi than cuckolded ones, indicating larger body size. Hence, extra food provisioning and early breeding reduced the occurrence of EPO in lesser kestrels. In addition, we confirmed the occurrence of intraspecific brood parasitism, as five nestlings were not the offspring of the brooding female. The results of our food-provisioning experiment support the idea that mate-feeding ability is a reliable indicator of male quality, and are in accordance with the hypothesis that male mate-feeding behaviour is a sexually selected trait.