麻豆社

How can canaries sing continuously for minutes on end? Between the notes it takes mini-breaths to replenish its air supply. It can do this 30 times a second in full song. A bird's voicebox can also produce two notes simultaneously because it lies deep in the bird's chest and not high in the throat like ours. Low notes come from one side of the chest and high notes from the other. By alternating between high and low notes, even short songs can be made to carry very complex messages. The cowbird, for example, has the most complex song of any bird, with over 40 notes in its songs. Some of the notes are so high they are beyond human hearing. It can take a cowbird two years to learn its song.