Animal vocal communication ranges from simple to complex based on repertoire size, structure, and 16 composition of calls and the information encoded in them. According to the social complexity hypothesis, 17 communication complexity tends to increase with an increase in social complexity. While several studies on 18 mammalian systems exist supporting this, evidence from avian systems is comparatively limited. Towards this, 19 we present evidence for complex acoustic communication in a cooperatively breeding passerine, Jungle Babbler, 20 based on three aspects of complexity: an extensive repertoire of acoustically-distinct calls, within-call structural 21 complexity and the diverse behavioural contexts in which these calls are used. Jungle Babblers were found to 22 possess a structurally and functionally diverse vocal repertoire comprising 15 different calls. Detailed acoustic 23 analyses of multisyllabic calls revealed that these calls are composed of different notes. Further, despite a large 24 number of notes present in the repertoire, the number of calls were limited to 15. This implies that there may be 25 underlying rules that determine call composition to give rise to functional calls to which receivers respond. We 26 also found that these calls were produced in a variety of affiliative and agonistic contexts and were employed 27 towards coordination of diverse social behaviours including group movement, foraging, brood care, aggression 28 and vigilance. Yet, 7 out of 15 vocalizations were produced in the context of vigilance. This disproportionate 29 investment of vocalizations towards co-ordinated acoustic vigilance is characteristic of many cooperatively 30 2 breeding birds. Our study extends support for the social complexity hypothesis and also lays the foundation for 31 future investigations on combinatorial and syntactical rules underlying call structure and function in bird 32 vocalizations. 33 34 Significance statement 35 Studies on vocal complexity in birds have focussed mainly on repertoire size, structure and function. However, 36 fine temporal and spectral features of elements that constitute a call/song are rarely examined to evaluate vocal 37 complexity. We examined complex communication in a cooperatively breeding social passerine, Jungle Babbler 38 for which we assessed repertoire size, function, acoustic features of calls and of their constituent elements. 39Jungle Babblers were found to possess a structurally and functionally diverse vocal repertoire comprising of 15 40 calls, 46% of which were in the context of vigilance, thereby extending support to the social complexity 41 hypothesis. We also found that several calls were composed of multiple, acoustically distinct notes. These 42 findings will be foundational in understanding the interrelations between sociality and communicative 43 complexity and underlying combinatorial rules that determine call structure and function. 44 45

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Time is an important and limited resource that can drive the trade-off between various essential activities in the lives of animals. Group-living animals need to perform different behaviour to meet their individual needs and also participate in group activities. They must, therefore, partition the available time between these activities which may vary considerably with environmental and ecological conditions. We examined time-activity budget of a cooperative passerine, Jungle Babbler (Argya striata) and how their behaviour vary across diel and seasonal scales. A repertoire of 13 behaviour was recorded of which 12 behaviour that occur throughout the year were examined further in detail. This included individual behaviour such as foraging, grooming, rest, shower and group behaviour such as allogrooming, movement, play, sentinel, mobbing and inter-group fight. Our results indicate that most of the time (about 70%) was spent performing individual behaviour and the remaining time (about 30%) was allocated to social behaviour. We also found almost all behaviour varied across diel and seasonal scale with respect to proportion of time spent performing them. This highlights the impact of environmental factors on how animals partition their time to perform various activities. Our study also lays the foundation for future studies examining the role of ecological factors such as habitat type and predation pressure in driving these patterns of behaviour in Jungle Babblers.