Alarm Vocalisations in Australian Birds: Convergent Characteristics and Phylogenetic Differences

SummaryAlarm vocalisations were recorded from 30 species of birds in Australia, 25 passerines (including 12 honeyeaters), two parrots, two raptors and one kingfisher. The calls were recorded both fortuitously, when birds called in the presence of wild predators, and by design, when a stuffed or tame owl was presented in field locations. Spectrographic analysis revealed several types of alarm calls: (1) broad frequency calls (0.6–3.5 kHz to 6–10 kHz range, 29 species) that have a harmonic or noisy structure; and (2) narrow frequency calls (1–3 kHz to 2–5.5 kHz range, 10 species) that are whistles or tones. Broad frequency alarm calls have similar structural components across a wide range of species. The nine species that emitted both broad and narrow frequency alarm calls tended to produce these in different predator contexts, with narrow band calls elicited by flying predators and broad band calls elicited by other threats. However, six species of honeyeaters alternated between narrow and broad band calls during mobbing and in response to terrestrial intruders, including humans. In the northern hemisphere many passerine species have high frequency alarm calls (up to 8 kHz, Marler 1955, 1957) that are not easily detected by airborne predators. The Australian species investigated here had lower frequency alarm calls which could be detected by airborne predators. Thus, the Australian species may be utilising a different method of avoiding predators.