Extra-pair copulations in male and female Azure-winged Magpies (Cyanopica cyanus) exhibit different associations with multiple intrinsic and extrinsic factors

While numerous studies on extra-pair copulations (EPCs) have revealed that the occurrence of this alternative reproductive strategy depends on multiple intrinsic and extrinsic factors, the relative contributions of these factors to EPC occurrence remain poorly quantified. To address this question, we investigated EPC behavior in the Azure-winged Magpie ( Cyanopica cyanus ) using an 11-year dataset. We first examined how EPC occurrence in females and males was associated with three kinds of factors: individual condition, ecological constraints, and social contexts. Then, we assessed the potential ecological consequences of EPCs, including effects on offspring phenotypic traits and microsatellite heterozygosity, and nest predation risk from natural predators and conspecific nest-raiders. Our results revealed that female EPC occurrence was negatively associated with individual body condition but positively associated with nesting density, whereas male EPC occurrence was unrelated to individual body condition but positively associated with habitat area and the proportion of cooperative breeding nests in the colony. Extra-pair partners of cuckolding females had significantly greater body mass than their social mates, but no such difference was observed between extra-pair partners and social mates of cuckolding males. Extra-pair young and within-pair offspring exhibited no significant differences in phenotypic traits and microsatellite heterozygosity. However, nests containing cuckolding individuals had significantly lower predation risk from predators but not from conspecific nest-raiders. Our findings suggest that female and male Azure-winged Magpies differentially weigh individual condition against shared natural or social factors when adopting EPC strategies, highlighting sex-specific tradeoffs in reproductive decision-making.