Which acoustic parameters modify the great tit’s response to conspecific combinatorial mobbing calls?

Abstract

When responding to a conspecific call, especially when mobbing a predator, receivers rely on acoustic cues produced by callers. Variation in calls, either gradual or discrete, can inform potential mobbers about the situation. Great tits use a combinatorial call made of frequency modulated elements (FMEs) and D notes. The gradual properties of the D notes change when facing different situations (e.g., different predators). We tested the relative effect of the number of D notes per call or the number of calls per minute on the behaviour of great tits with a playback experiment on free-ranging tits. Great tits did not change their approach behaviour depending on the treatments broadcast. However, they increased their vigilance level with an increased number of D notes in the total sequence. We propose that great tits can consider the overall amount of D notes as a form of information about the predator being mobbed. In addition, an increased number of D notes did not modify the approach behaviour but modified the vigilance behaviour, possibly indicating that great tits process the complete FME-D call as a whole mobbing unit rather than the simple sum of a vigilance call (FME) and a recruitment call (D notes). Our study enlightens the coding system of great tits when mobbing a predator and more generally how animals can combine simple syntactic rules and gradual variations when communicating. Significance StatementInformation transfer when communicating about a predator is well described, particularly when mobbing a predator. However, it is unclear which specific variable(s) receivers rely on when adapting their response. Here, we test whether great tits adapt their response when the number of calls per minute and/or the number of notes 2 per call is increased. Our results indicate that great tits rely on the overall number of notes in a calling sequence as a proxy for urgency. We also propose that the combinatorial call they use when mobbing is considered as a whole rather than the simple sum of its constituents. Understanding how information transfer occurs in birds using combinatorial calls instead of simple note repetition adds to the current insights about compositional syntax in animals.

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

“…Interestingly, a recent study found that the approaching behaviour of great tits towards conspecific mobbing calls does not depend on the calling rate broadcast (Salis et al, 2022). However, since different calling rates were used in both studies (present study: high‐calling rate: 60 calls per min vs. low‐calling rate 20 calls per min; Salis et al, 2022: high‐calling rate: 30 calls per min vs. low‐calling rate 15 calls per min), and different populations may respond differently to calls even of their own species, depending on their ecological community, future studies in the present study population are needed. Specifically, future playback experiments investigating the responses of great tits to conspecific calls should use a high‐calling rate with 40 calls per min since our results suggest that this calling rate is given during very high‐risky situations.…”

“…Importantly, future studies are needed to investigate (a) if great tits respond as strongly as to high‐urgency calls of Southern house wrens as they do to high‐urgency calls of conspecifics and (b) if the response difference between high‐urgency and low‐urgency calls is similar for conspecific playbacks versus the house wren playbacks. Interestingly, a recent study found that the approaching behaviour of great tits towards conspecific mobbing calls does not depend on the calling rate broadcast (Salis et al, 2022). However, since different calling rates were used in both studies (present study: high‐calling rate: 60 calls per min vs. low‐calling rate 20 calls per min; Salis et al, 2022: high‐calling rate: 30 calls per min vs. low‐calling rate 15 calls per min), and different populations may respond differently to calls even of their own species, depending on their ecological community, future studies in the present study population are needed.…”

“…We kept a minimum distance of at least 200 m between experimental sites. However, it is possible that some resampling occurred since great tits were not marked (but see Salis et al, 2022).…”

Acoustic cues and season affect mobbing responses in a bird community

“…We did not use a negative control (e.g., heterospecific song or background noise) since we were interested in the difference between our treatments. Moreover, background noise has been used in several studies (Dutour et al 2019, Salis et al 2022, Suzuki et al 2016) and never triggered a response from Parids. We used recordings obtained by A.S. during the previous year in the same area where the experiment took place.…”

“…We did not use a negative control (e.g., heterospecific song or background noise) since we were interested in the difference between our treatments. Moreover, background noise has been used in several studies (Dutour et al 2019, Salis et al 2022, Suzuki et al 2016) and never triggered a response from Parids. To prepare our soundtracks, we elicited mobbing calls from wild crested tit and coal tit by broadcasting a mobbing chorus of various birds (including coal and crested tits, Dutour et al 2016).…”