The social intelligence hypothesis posits that complex social interactions drive cognitive evolution in animals. However, empirical support remains inconsistent, likely because most studies rely on crude measures like group size rather than examining the nuanced patterns of individual social interactions. Additionally, while cognitive sex differences are well-documented across species, whether these differences stem from sex-specific social interaction patterns remains unclear. To address these gaps, we investigate how individual-level social complexity and nuanced social interactions influence cognitive performance in Budgerigars (Melopsittacus undulatus). Birds were reared in mixed-sex groups. We quantified social complexity and nuanced social interactions before testing cognitive performance across four tasks. Our results indicated that general intelligence did not predict performance across tasks in Budgerigars, supporting a modular rather than general intelligence framework. More importantly, social complexity effects on cognitive performance were both sex- and task-dependent. Competitive interactions, rather than affiliative ones, positively influenced spatial memory performance, but the specific patterns differed between sexes. Males showed enhanced spatial memory performance with higher overall frequency and variability of competitive interactions, while females showed improved spatial memory with a higher proportion of competitive interactions toward specific individuals and greater interaction variability. These findings demonstrate that cognitive performance is associated not just with social complexity, but with the nuanced structure of social interactions, and that these relationships are shaped by sex-specific strategies and domain-specific cognitive abilities. Our results highlight the critical importance of moving beyond simple group metrics to understand the social drivers of cognition.