Sociality can provide many benefits, including increased foraging success, reproductive opportunities, and defence against predation. How does sociality influence the dominance hierarchies of ecological competitors? Here, we address this question using a large citizen science dataset of competitive interactions among birds foraging at backyard feeders, representing a network of over 55,000 interactions among 68 common species. We first show that species differ in average group size (the number

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... f conspecifics observed together) as a fundamental measure of sociality. When analyzing heterospecific competition, we find that sociality is inversely related to dominance. On average, a single individual from a solitary species is more likely to displace a size-matched opponent than a single individual from a social species. Yet, social species tend to gain an increase in their competitive advantage when in the presence of their conspecifics. Finally, we show that more social species have relatively fewer dominance interactions with heterospecifics, and more with conspecifics. Overall, these results demonstrate that sociality can influence competition in ecological networks. More social species have decreased competitive ability as individuals, but they may gain competitive ability in groups.