After dark during the breeding season, it calls with great persistence. A bird s song is an audible fence. It announces to rivals that the singer s territory is taken and will be defended. That saves a lot of needless fighting. The songs of spring are triggered by hormones, which may swell a male bird s gonads, or primary sex glands, to 400 times their normal size and weight.
Song is essential.
They depend entirely on voice to locate mates and rivals. But the bird is perfectly disguised to blend with her surroundings. Except when feeding, she stays on top of her clutch until the eggs hatch. Clutch size is about 2 eggs. This survey is typically performed in June by volunteers on over 4000 bird counts.