Avian nests face a wide variety of nest predators, which pose different risks that could select for the ability of parents to notify conspecifics of nest predator type. We previously demonstrated that the Japanese Tit (Parus minor) produces acoustically distinct mobbing calls for different nest predators (crows and snakes), thereby eliciting different and appropriate anti-predator responses not only in parents, but also in nestlings. However, the variation in mobbing call behavior may have been caused by differences in the experimental methods used, whereby each nest was presented with either a mounted crow or a live caged snake. In the present study, we observed a total of seven natural encounters of Japanese Tits with crows (n = 4) and snakes (n = 3) near their nests. Consistent with the previous experiments, Japanese Tits produced distinct mobbing calls, namely, “chicka” calls for crows (4/4) and “jar” calls for snakes (3/3). Thus, we conclude that mobbing calls of Japanese Tits signal nest predator type to both parents and nestlings.