Academic Reading — All-Types Test 4

Reading passage

The Science of Birdsong A Birdsong is one of the most familiar sounds in the natural world, yet the mechanics behind it remain surprisingly intricate. Unlike humans, who produce sound in the larynx, birds sing using an organ called the syrinx, which sits deep in the chest at the point where the windpipe divides into the two lungs. Because the syrinx has two branches, many species can generate two independent streams of sound at once, effectively singing a duet with themselves. This anatomical arrangement gives birds a range and flexibility that far exceed anything the human voice can achieve, and it explains why a bird no larger than a sparrow can fill a garden with such volume and variety. B Not every sound a bird makes counts as song. Ornithologists draw a careful line between calls and songs. Calls tend to be short, simple and instinctive; they warn of predators, keep a flock together, or signal the location of food. Song, by contrast, is usually longer, more elaborate and, crucially, often learned rather than inherited. In most species it is the male that sings, chiefly to defend a territory and to attract a mate. A rich, complex song can advertise that its owner is healthy, experienced and worth breeding with, which is why females of many species pay close attention to the quality of what they hear. C How young birds come to sing has fascinated researchers for decades. In a number of songbird species the process closely resembles the way a human infant acquires speech. A nestling first listens to the song of an adult tutor, usually its father, and stores a memory of it. Later, once it begins to vocalise, it produces a rambling, unstructured version known as subsong, which is often compared to the babbling of a baby. Over the following weeks the young bird gradually refines these attempts, matching what it hears itself sing against the stored template until the two align. Should a chick be raised in isolation, hearing no adult of its own kind, it will grow up singing only a crude and incomplete song. D The timing of this learning is strict. Many species have what is called a sensitive period, a window early in life during which the brain is especially receptive to acquiring song. If a bird misses this window, it may never sing normally, however much it is exposed to a tutor afterwards. Research at a field station in the Welsh borders has shown that some species can add new phrases throughout their lives, while others fix their repertoire after the first year and never change it. The difference appears to be linked to specialised clusters of brain cells that either remain flexible or harden into a fixed pattern. These findings have practical value as well, for a bird kept as a pet may fail to develop its full natural song if it is removed from its parents too early, before it has had the chance to memorise a proper model. E Song also carries a great deal of information beyond the simple identity of the singer. The dialect of a song can reveal where a bird was raised, since populations in different valleys often develop subtly distinct versions of the same basic tune. Small variations in pitch and rhythm can betray a singer's age or condition, and rivals listen closely for any sign of weakness. In this sense a garden at dawn is far from the peaceful scene it appears to be; it is a landscape crossed by invisible boundaries, each one announced and defended in sound. F For all that scientists have learned, much about birdsong remains unexplained. Why some species command a repertoire of hundreds of distinct phrases while their close relatives repeat a single note is still debated. What is clear is that song is not mere decoration. It is a tool shaped by evolution, as vital to a bird's survival and reproduction as its feathers or its beak, and every spring chorus is the audible edge of a contest that has been running for millions of years.