The complex songs of two molossid species

Abstract

Birds are well known for songs while bats are well known for their developed sonar system. The chiropteran echolocation system has a long and extensive history of research because of the highly specialized neurocircuitry required for vocal production, perception, and vocal-motor integration. However, recent research has revealed that in addition to echolocation, bats produce highly sophisticated social vocalizations whose complexity is only rivaled by birds, humans, and cetaceans. In this chapter we discuss and define the terms “song” and “courtship call”, outline how acoustic signals are analyzed, and review what families of bats produce songs and calls. We then compare behavior, song structure, individual variation, and regional dialects in two species of Molossids, Tadarida brasiliensis and Nyctinomops laticaudatus. T. brasiliensis is a bat that sings like a bird-they produce songs with three key songbird features: hierarchical structure, syntactical organization, and syntactical flexibility. T. brasiliensis songs are composed of four main syllable types: chirp A (“A”), chirp B (“B”), trill and buzz. Syllables are combined to form three phrases, chirp, trill, and buzz and phrases are then combined to form songs (hierarchical structure). Specific syntactical rules are followed for combining phrases (syntactical organization). However, the number of syllables within a phrase and the number and order of phrases vary from one rendition to the next (syntactical flexibility). N. laticaudatus produce the same types of syllables and phrases as T. brasiliensis. However, the spectro-temporal structure of A and B syllables of N. laticaudatus are quite different, and they show much lower syntactical flexibility in combining phrases. Finally, while T. brasiliensis males produce highly stereotyped chirp syllables that do not vary between regions, N. laticaudatus chirp syllables are not stereotyped within males but do vary across regions. These findings are the first to show that complex songs are not only produced by a single bat species and that many aspects of songs are highly conserved across species.