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

Abstract

Alarm calls are an antipredatory strategy widely used by animals. Some calls are functionally referential, giving specific information about the perceived threat. In other cases, the calls are less specific although they may also provide information about the level of threat or “urgency.” Here, we assess whether southern house wrens (Troglodytes aedon bonariae) provide information about the level of risk when they perceive a threat during nesting. We analysed the call acoustic structure and repetition rate of calls emitted by the breeding pair when we placed a model of a predator at different distances from the nest. The results showed that, although there were no structural differences in alarm calls among treatments, individuals increased the rate of alarm calling according to the distance of the predator model from the nest, reflecting a perceived level of threat. Playback experiments of alarm calls reproduced at different rates also showed that recruitment of conspecific and heterospecific individuals increased with the calling rate. These experiments showed that the rate of alarm calling in the southern house wren provides information about the perceived level of risk and that listeners respond accordingly.

How great tits respond to urgency‐based information in allopatric Southern house wren mobbing calls

“…We built 1‐min sound files by repeating these calls at either 60 calls/min for 4 high‐calling rate files or at 20 calls/min for 4 low‐calling rate files (one individual's call per file). These calling rates roughly corresponded to the maximum rates per minute observed in the high‐risk (with the predator model at <0.3 m from the nest) and low‐risk (with the model at 3 m from the nest) experiments (see Fernández & Carro, 2022 for more details).…”

“…For all playbacks, we used “Type I” mobbing calls that were previously recorded from house wrens between 2013 and 2015 near General Lavalle, Buenos Aires province, Argentina (36°20′S, 56°54′W) ( N = 4, Figure 1; Fernández & Carro, 2022). These calls are produced when house wrens are confronted with threats during nesting and have a frequency that varies from 1 to 9 kHz (reaching a peak frequency at 4–6 kHz) and a duration of between 0.4 and 0.6 s (Fernández & Carro, 2022). The “Type I” calls were elicited by exposure to a human at different distances from the nest boxes.…”

“…Mobbing calls of the house wrens are composed of a single note (Figure 1, Fernández & Carro, 2022), whereas mobbing calls produced by the great tits and the Eurasian wrens are more complex (Figure 1). Great tits produce mobbing calls made of two parts: a few frequency‐modulated elements, which are then followed by a string of broadband frequency notes (D notes, Figure 1, Dutour et al, 2019).…”

“…The "Type I" calls were elicited by exposure to a human at different distances from the nest boxes. Calls were recorded using a Fostex FR-2 LE solid-state recorder (Fostex Company; sampling rate: 44.1 kHz; accuracy: 16-bit; file format: WAV) with a Sennheiser K6/ME66 shotgun microphone (Sennheiser Electronic GmbH & Co. KG; see Fernández & Carro, 2022 for more details). We selected for playback four calls from each of four individuals.…”

“…This study investigated whether the great tit could perceive information about urgency in mobbing calls given by an allopatric non‐Paridae species, the Southern house wren ( Troglodytes aedon bonariae , Figure 1). Southern house wrens encode urgency information in their mobbing calls by increasing the rate of alarm calling in response to closer threats, to which conspecifics and sympatric heterospecifics respond appropriately (Fernández & Carro, 2022). Great tits encoded urgency in a similar way to that of wrens, by increasing the rate of alarm calling according to the level of the threat (Carlson et al, 2017; Kalb et al, 2019).…”