Assertion: wren's song | /r/HasProperty | parker
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Source sentences:
text: Juveniles often use an indefinite, quiet warble that is less loud and precise than the adult territorial song (Anderson 1973; Parker 1986; Ricklefs 1973; Armstrong 1955; Ricklefs 1968; Simons and Simons 1990; Robbins 1966; Udvaldy 1994).