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Altricial birds show enormous intraspecific diversity in their provisioning strategies, in terms of both the provisioning rate and the amount of food delivered per feeding bout. Extra‐pair copulations (EPCs), which result in either extra‐pair paternity (EPP) or maternity (EPM), provide an opportunity to demonstrate why provisioning strategies vary among individuals. Because EPP‐cuckolded males and EPM‐cuckolded females must raise unrelated young, whereas EPM‐cuckolded males and EPP‐cuckolded females need not, we hypothesized that the first two categories of breeders would reduce parental effort, whereas the latter two categories of breeders would increase parental effort. We tested this hypothesis in the Azure‐winged Magpie Cyanopica cyanus by comparing the number and body mass of fledglings, provisioning rates and food amount delivered per feeding bout between EPP‐ and EPM‐cuckolded breeders and faithful breeders. We found that (1) the number of fledglings did not differ significantly between cuckolded and faithful breeders, and (2) fledglings raised by EPM‐cuckolded males and EPP‐cuckolded females did not differ from faithful breeders, whereas fledglings raised by EPP‐cuckolded males and EPM‐cuckolded females were significantly smaller than those raised by faithful breeders. Compared with faithful breeders, cuckolded breeders increased parental efforts in nests that contained no unrelated young; hence, their loss in parentage may be compensated for by the enhanced quality of fledglings. In nests that contained unrelated young, cuckolded breeders did not reduce parental efforts; hence, their own offspring would not starve and could survive in competition with mixed brood‐mates. Our findings suggest that the differences in parentage created by EPP and EPM scenarios and the potential fitness return of raising a brood for the cuckolded breeders can explain the intraspecific variation in provisioning strategies of altricial birds.

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