Structure and function of the vocal repertoire of the Rifleman ( Acanthisitta chloris ), a member of the earliest diverging passerine suborder, Acanthisitti

Birds communicate primarily using vocal signals. These signals undergo strong selection for effective transmission, which is often critical for survival. Passerines are an excellent group for studying vocal communication due to their diverse vocal repertoires, from simple calls to complex songs. However, the study of songbird calls is often overshadowed by studies of more conspicuous songs, which may bias our understanding of the true diversity of bird vocalizations. Here, we detail the vocal communication system of the Rifleman ( Acanthisitta chloris ), a New Zealand Wren (family: Acanthisittidae), a songless species from a species-poor suborder (Acanthisitti), sister to the oscine and suboscine Passerines. We describe nine adult call types and three juvenile call types, providing the most complete vocal repertoire of this species to date. Within these call types, we found variation in the spectral acoustic structure between different behavioral contexts. Furthermore, we also found negligible differences between sexes in contact calls, despite substantial size dimorphism. Using these data, we classify call types and discuss their probable function(s) based on behavioral context, such as foraging, provisioning nests, nuptial feeding, and alarm calling. Collectively, we hope that this study will provide a foundation for understanding the evolution and function of calls in Passerines and encourage more study of calls across taxa.