DOI: 10.5061/dryad.rbnzs7hm8
title: Pair-coordinated calling: Eurasian magpies respond differently to simulated intruder pairs that overlap or alternate their calls

description: Animal vocalisations are widely used to signal strength or motivation of a
 caller in competitive interactions, such as in territorial defence.
 Substantial understanding of signalling functions in territorial conflicts
 is based on singing by male songbirds. Yet, in many species, both pair
 members call during territorial conflicts, as well as in predator-induced
 situations, leading to complex signalling interactions in which calls
 overlap or alternate. This raises the question as to whether or not
 variation in how individuals in pairs time their calls is perceived as
 meaningful by receivers. Here, we tested with playback experiments whether
 Eurasian magpies (Pica pica), a species producing alarm calls (so-called
 chatter calls) in territorial defence, respond stronger to simulated
 pair-intruders who overlap their calls with each other than to those who
 alternate them. Magpies emitted a significantly longer first chatter in
 response to playback with overlapping call but tended to more closely
 approach the loudspeakers playing back alternating (and therefore longer)
 call sequences. These findings exemplify that the timing of calls by pair
 members matters, but in more complex ways than we predicted. The
 overlapping playback appeared to trigger a stronger initial chatter
 response but a weaker approach response, suggesting that the different
 ways in which magpies respond reflect different levels of arousal or
 defence strategies. These findings expand on classical experiments on call
 function, suggesting that pairs can vary the message by coordinating their
 alarm calls in different ways, similar to how duetting pairs time their
 song contributions in advertisement signalling.
description: We conducted playback experiments simulating a territorial
 intrusion by a pair of magpies were the timing of calls from the pair
 members differed. Specifically, we used two loudspeakers broadcasting
 chatter-calls with the calls from the second speaker either alternating or
 overlapping the calls from the other loudspeaker. The playback trials were
 conducted in the vicinity of magpie nests. A trial consisted of one minute
 playback plus two additional minutes observation time. During the trial,
 we recorded magpie vocal responses and noted the closest approach distance
 to the loudspeakers of any magpie. Audio recordings were analysed in
 Audacity® v3.1.3 (Audacity Team, 2023) by setting labels over all chatter
 calls and overlapping chatter sequences. Those labels were exported as
 text files and merged with trial data in R v4.3.2 (R Core Team, 2023). We
 used the packages tidyr v1.2.0 (Wickham & Girlich 2022) and dplyr
 v1.0.8 (Wickham et al. 2022) to extract for each trial a) the closest
 approach distance of magpies to the speakers, b) the total number all
 chatter calls (including those that overlap with another) and total
 duration of chattering (i.e. total duration of all single chatter calls
 and overlapping chatter sequences), and c) the number of overlapping
 chatter sequences. For those trials in which chattering occurred, we
 further extracted d) the latency between the start of the playback and the
 first chatter and e) the number of syllables of the first chatter. This
 dataset contains the resulting summary file per trial. The details of the
 methods are described in the manuscript itself
description: # Pair-coordinated defence: Overlapping calls alter territorial responses
 in Eurasian magpies
 [https://doi.org/10.5061/dryad.rbnzs7hm8](https://doi.org/10.5061/dryad.rbnzs7hm8) This dataset contains the general trial information and measured response variables for a two-loudspeaker playback experiment, described in the manuscript, as well as the R code with which we analysed and plotted the data. We played back Eurasian magpie chatter-calls close to nests of Eurasian magpies and measured vocal and approach responses to the playback. We were interested if the timing of calls (i.e., overlapping or alternating calls) of a simulated intruding pair would affect how receivers respond to the playback, assuming that a stronger response indicates that the playback is perceived as a stronger signal. Both playback types were broadcasted at each playback site, with two to five days between experiments at the same location. ## Description of the data and file structure The dataset is structured in a table with one row per trial, with relevant trial information and response variables in columns. If no magpies were present during the first round of playback and a second round was conducted, then the response variables of the second trial were given and the round specified in an extra column. We used NA to indicate if no data was available for a specific column (e.g., if no magpies were present or vocalised). These are the column names and respective explanations: | Column name | Description | | :-------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Trial | Trial identifier in the form YY-TpbXXX | | Date | Date at which the trial was conducted, in the forn dd/mm/YYYY | | Time | Time at which the trial was conducted, in the form hh:mm:ss | | NestLocation | Nest identifiers at which the playback was conducted. In few cases, more than one nest was located close to the playback site. | | Coordinates | Coordinates of the trial location | | Treatment | Playback type that was used for the trial, either using alternating or overlapping chatter calls | | Replicate | Identifier of the playback replicate used in the trial | | TrialSeq | specifies if this was the first (1) or second (2) trial at this location | | nRounds | Round number of the trial data (1 if magpies were present during the first playback round of a trial, two if magpies were neither seen nor heard during the first playback round and therefore the playback was started a second time) | | Cat | indicating if a cat appeared during the trial and therefore all subsequent vocalisations were excluded | | binomPresent | binomial if magpies were present during the playback | | binomChat | binomial if magpies chatter-called during the trial | | binomOv | binomial if overlapping chatter sequences occurred during the trial | | nSinChatter | Number of single chatter calls | | nChatOv | Number of chatters that overlap another chatter call | | novChatSeq | Number of overlapping chatter sequences | | nAllchat | Number of all chatter calls | | totSinchatdur | Total duration of all single chatter calls, in seconds | | totovChatdur | Total duration of all overlapping chatter sequences, in seconds | | totChatdur | Total duration of all single chatter calls and overlapping chatter sequences, in seconds | | latChat1 | Latency from the playback start to the first chatter, in seconds | | latovChat1 | Latency from the playback start to the first overlapping chatter sequence, in seconds | | latanyChat | Latency from the playback start to the first single chatter or overlapping chatter sequence, in seconds | | SylChat1 | Number of syllables of the first chatter call | | latAppear | latency until we first noticed a magpie (zero if they had been seen or heard prior playback start) | | stClosestDistAny | Closest approach distance, i.e. the closest distance between the loudspeakers and the magpie that approached closest during the trial, measured in meters | | standNmagpies | Number of magpies present during the trial | | FledgePresent | y (yes) or n (no) for if fledglings were present during the trial | | distObs-Speaker/Model | Distance between the observer and the loudspeaker during the trial, measured in meters | | distSpeaker-Speaker | Distance between the two loudspeakers, measured in meters | | Trial\_PB1 | Trial identifier from which the first chatter was extracted for playback | | Lat\_PB1 | Latitude of the location from where the first chatter was extracted for playback | | Lon\_PB1 | Longditude of the location from where the first chatter was extracted for playback | | Trial\_PB2 | Trial identifier from which the second chatter was extracted for playback | | Lat\_PB2 | Latitude of the location from where the second chatter was extracted for playback | | Lon\_PB2 | Longditude of the location from where the second chatter was extracted for playback | | T.lat | Latitude of the trial location | | T.lon | Longditude of the trial location | | PBdist1 | Distance in meters between the trial location and the location from where the first chatter was extracted for playback | | PBdist2 | Distance in meters between the trial location and the location from where the second chatter was extracted for playback | The second file contains the R code with which the data were analysed.