The occurrence of mixed-species foraging flocks is a worldwide phenomenon in terrestrial bird communities. Previous studies suggest that individuals participating in flocks might derive benefits in terms of improved feeding efficiency and/or reduced risk of predation. However, very little is known about how individuals establish mixed-species flocks. Here, I provide the first experimental evidence that long-distance calling by the willow tit, Poecile montanus, facilitates the establishment of mixed-species flocks at a foraging patch. Observations at experimental foraging patches showed that willow tits that find a food source produce long-distance calls, particularly when they are isolated from conspecific flockmates. The probability of long-distance calling was negatively correlated with the number of heterospecific foraging individuals near the food source. A playback experiment confirmed that calls attract both conspecific and heterospecific members of foraging flocks. This study demonstrates that willow tits use long-distance calls to attract conspecific flockmates to foraging patches, and these calls can also facilitate the formation of mixed-species flocks on patches.