Animal feeding behaviour is of key importance for individual fitness, and is strongly affected by inter-individual information transfer and competition. Studying such causal relationships are especially challenging for elusive taxa like bats. Bats increase their food search efficiency by being attentive to behaviour of other individuals, and adjust their behaviour either to avoid or increase the competition with them. The few studies available about the density dependence of competition show that small group size benefits to bats in search of food, while greater groups become less advantageous due to interferences (such as acoustic call overlap). Studies have so far focused on competition mechanisms (e.g. intentional acoustic interference towards other individuals), but none to our knowledge has assessed the consequences of the density dependence on foraging efficiency. Using 3D flight path reconstruction systems from echolocation calls of wild bats, we sampled hundreds of flight trajectories at two French regions (~60 sites) for several species, each exhibiting a gradient in foraging intensities and bat densities. We extracted information on flight behaviour (e.g. flight speed) and prey capture attempts (acoustic signatures). We tested the hypothesis of an optimal foraging theory, i.e. an increase in prey capture success as the number of conspecifics increases (by facilitation), followed by a decrease when the number of congeners becomes too great (by competition). We also hypothesized that these inter-individual relationships should have consequences for the energetically optimal flight strategy when hunting (e.g. lower flight speed), pushing individuals out of this optimal zone to maintain their competitiveness in the presence of other individuals. Overall, we found that individuals can cooperate to forage, but that this can have consequences for the flight behaviour of individuals, who have to opt for suboptimal flight to keep a given feeding rate. Such results will help to understand the mechanisms of species coexistence and the likely consequences of human activities on bat populations. This is especially true for the artificial light at night which deeply alters the spatial distribution of bat prey, leading to many areas with no food resource, and a few with many where competition could have detrimental consequences on the physiology of individuals.