Abstract
Northern Bald Ibis are socially monogamous and year-round colonial birds with a moderate repertoire of calls. Their ‘croop’, for example, is used during greeting of mates, but also during agonistic encounters, and provides an ideal case to study whether calls are revealing with respect to motivational states. We recorded croop calls in a semi-tame and free-roaming flock of Northern Bald Ibis in Austria, and analysed the vocal structure to identify parameters (e.g. call duration, fundamental frequency) potentially differing between social contexts, sexes and individuals. Additionally, we conducted playback experiments to test whether mated pairs would discriminate each other by their greeting croops. Acoustic features showed highly variable temporal and structural parameters. Almost all calls could be classified correctly and assigned to the different social contexts and sexes. Classification results of greeting croops were less clear for individuality. However, incubating individuals looked up more often and longer in response to playbacks of the greeting calls of their mate than to other colony members, indicating mate recognition. We show that acoustic parameters of agonistic and greeting croops contain features that may indicate the expression of affective states, and that greeting croops encode individual differences that are sufficient for individual recognition.
Highlights
IntroductionIndividual recognition is important in many social contexts [1], and several sensory channels can be used for this purpose, either separately (visual: e.g. [2], and olfactory: [3], [4]) or combined (visual and acoustic: [5])
Individual recognition is important in many social contexts [1], and several sensory channels can be used for this purpose, either separately or combined
We found that Northern Bald Ibis croop calls differed between social contexts and sexes, but to a lesser extent between individuals
Summary
Individual recognition is important in many social contexts [1], and several sensory channels can be used for this purpose, either separately (visual: e.g. [2], and olfactory: [3], [4]) or combined (visual and acoustic: [5]). Individual recognition is important in many social contexts [1], and several sensory channels can be used for this purpose, either separately Most studies on acoustic individual recognition have been conducted in oscine passerines, which have large and complex song and call repertoires. In non-passerines, which have received comparatively less attention in acoustic studies, individually distinct vocalisations may rely on morphometric differences with a high genetic influence [6]. Individual recognition is not limited to the phylogenetic taxonomy but should rather evolve whenever social context requires repeated individualised interactions [1]. Biparental care is common [12] and requires repeated interactions among mated pairs, as both have to coordinate actions to optimise their investment [13],[14]. The ability of individual recognition should be beneficial and selected for [15]
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