Speedy revelations: how alarm calls can convey rapid, reliable information about urgent danger

Abstract

In the perpetual struggle between high-speed predators and their prey, individuals need to react in the blink of an eye to avoid capture. Alarm calls that warn of danger therefore need to do so sufficiently rapidly that listeners can escape in time. Paradoxically, many species produce more elements in their alarm calls when signalling about more immediate danger, thereby increasing the reliability of transmission of critical information but taking longer to convey the urgent message. We found that New Holland honeyeaters, Phylidonyris novaehollandiae , incorporated more elements in alarm calls given to more dangerous predators, but video analysis revealed that listeners responded in 100 ms, after only the first element. Consistent with this rapid response, the acoustic structure of the first element varied according to the danger, and playbacks confirmed that birds need hear only the first element to assess risk. However, birds hid for longer and were more likely to flee, after calls with more elements. The dual mechanisms of varying both element structure and number may provide a widespread solution to signalling rapidly and reliably about immediate danger.

Alarm calls of southern house wrens, Troglodytes aedon bonariae, convey information about the level of risk

“…In some species, callers use acoustically different calls to signal specific information about the perceived threat such as the predator type, size or location (Evans, Evans, et al, 1993; Farrow et al, 2017; Gill & Sealy, 2003; Seyfarth et al, 1980; Suzuki, 2011, 2015; Templeton et al, 2005). However, callers can also indicate the level or immediacy (“urgency”) of a threat by modifying the call structure and/or call parameters in relation to the degree of perceived risk (Evans, Macedonia, et al, 1993; Leavesley & Magrath, 2005; McLachlan & Magrath, 2020). In such urgency‐based alarm systems, calls may vary in their call rate, acoustic structure of the calls, and even the type of call according to the distance, approach speed and threat level of the predator.…”

“…For example, in domestic chickens ( Gallus gallus ), the number of calls uttered by individuals indicates the size and speed of aerial predators (Evans, Macedonia, et al, 1993). The Arabbian babbler ( Turdoides squamiceps ) use different calls depending on the distance from the predator (Sommer et al, 2012), and white‐browed scrubwrens ( Sericornis frontalis ) and New Holland honeyeaters ( Phylidonyris novaehollandiae ) use more elements in their aerial alarm calls when a predator is close or dangerous (Leavesley & Magrath, 2005; McLachlan & Magrath, 2020). Urgency‐based communication systems are thus characterized by a variation in the repetition rate or type of alarm call given according to the risk perceived by individuals and a matched response from the listening individuals.…”

A Cause for Alarm: Increasing Translocation Success of Captive Individuals Through Alarm Communication

“…Calls made at a lower frequency and slower speed are often classified as mobbing, recruitment or terrestrial calls (Kalb et al, 2019), because they are easily detectable to recruit others to the location of the predator to harass and deter it (Consla and Mumme, 2012). Upon detecting a high-risk predator, a number of fast and sometimes longer and higher frequency calls are made (Marler, 1955;Jurisevic and Sanderson, 1994;McLachlan and Magrath, 2020), which are classified as flee, aerial, or warning calls because they urge the listeners to hide and become difficult to be located by predators (Klump and Shalter, 1984;Igic and Magrath, 2014;Maziarz et al, 2018).…”

A study on the role of social information sharing leading to range expansion in songbirds with large vocal repertoires: Enhancing our understanding of the Great-tailed Grackle (Quiscalus mexicanus) alarm call

“…The alarm call vocalization in Q. mexicanus is known to vary in tone, range and pitch (Kok 1971). Alarm calls signal low intensity excitement (Kok 1971) and research in other species has shown that differences in the acoustic qualities of alarm calls reflect the urgency of threats tailored to the receiving audience (Carlson et al 2020, Sheldon et al 2020, McLachlan and Magrath 2020. However, due to the ecological importance of alarm calls in minimizing risk to group members, natural selection could promote stabilizing selection on alarm calls, resulting in homogenous alarm call structure across subspecies regardless of habitat and receiver.…”