The fertility announcement hypothesis proposes that avian males should sing at a high rate when their mate is fertile to guard their paternity. We examined if male Song Sparrows (Melospiza melodia) sing more during the incubation period when they are free of constraints of physical mate guarding. We assessed song rates of eight males for 1 hr-periods every 1–2 days during each breeding stage over two consecutive broods within one season. Males sang significantly more during periods when their mate was incubating than during the pre-fertile, or fertile periods, or while feeding young (second brood). Males may be singing at high rates during incubation to maintain contact with their mate and/or to advertise for extra-pair copulations.