The signal repertoire of the house wren. In contrast to the signals of the baboons illustrated in Figure 2, the signal repertoire of the house wren (Troglodytes aedon) (a, left panel), a common songbird, is diverse and highly structured . In this example, from a population from Western Canada, the repertoire consists of 27 different types of syllable (a, right panel), where each syllable type is composed of one, two, or in some cases three different individual notes. These syllables are then strung together in longer songs that involve the concatenation of multiple different syllable types. Within a song, each syllable type can be repeated several times before switching to the next syllable type. Further, there are consistent patterns in which syllable types co-occur within songs and in what order they typically appear. (b) Templates (right panel) for the 10 most common song types for Western Canadian wrens, three of which are illustrated in the spectrograms in the left panel. The values between syllable types within each song correspond to the transition probabilities between successive syllable types in a song. Regularities in the syllable constitution and syllable transition patterns of song types constitutes a rudimentary syntax.