Making music can be fun and relaxing. For gibbons(长臂猿) in the forests of Southeast Asia, singing is also a way to communicate.
    New research shows that these small apes vary the order of the notes in their tunes to get across certain messages. It’s the first evidence that apes use something called syntax, （句法）which is an early step toward humanlike language.
    Researchers studied 13 groups of white-handed gibbons in Thailand’s Khao Yai National Park. Between two and six gibbons lived in each group. Most groups contained a pair of adults and their offspring.（后代）
    White-handed gibbons are known for their loud songs. Pairs of adult males and females mate for life, and these pairs perform duets （二重唱）, often changing the tunes over time.
    To find out how gibbons react to predators(食肉动物), the researchers designed realistic models of predators. When the gibbons saw these “predators”, they responded with songs. Each song began with a series of soft notes that sounded like “hoo” and included many repeats of a second note.
    Hearing the songs, other gibbons could tell the difference between duets and warnings. When the songs they heard were inspired by predator sightings, for example, the animals waited for at least 2 minutes before calling back. And they loudly repeated the same set of notes.