Territorial song sparrows tolerate juveniles during the early song-learning phase

Avian song learning is an important model system for understanding vocal learning in humans and other animals. Laboratory studies indicate that social interactions are critical for song learning, but field observations show that territorial males are aggressive to intruders, raising the question of whether young birds are tolerated, much less tutored in the wild. We examined how adult song sparrows (Melospiza melodia) treat juvenile and adult intruders during different seasons important for song learning-summer, autumn, and spring-using taxidermic mounts and song playback. Territorial adults responded aggressively to adult intruders throughout the year. Adults were tolerant of juvenile intruders in the summer, displayed somewhat reduced aggression in the autumn, but treated juveniles like adult intruders by the spring. In the summer and autumn trials, wild juveniles approached our simulated "interactions" between subjects and adult mounts; these wild juveniles were also tolerated, even at close distances. That juveniles can and do closely approach adults during the early sensitive phase of song learning suggests that direct interactions with adults are possible and might be important for learning. In contrast, since young birds are treated aggressively in early spring, most late song learning likely happens through eavesdropping or long-distance singing interactions.