in territorial birds, males increase song production rate when neighbouring males encroach on their territory. in great tits ("parus major"), nightingales ("luscinia megarhynchos"), blackbirds ("turdus merula") and sparrows (family passeridae), playing song recordings slows the rate at which males establish territories in an unoccupied region, suggesting these birds rely on song output in establishing territorial boundaries. experimentally muted scott's seaside sparrow ("ammodramus maritimus") lose control of their territories to other males. thus, territorial birds often rely on song production to repel conspecific males.