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Dominance interactions and hierarchies are of long-standing interest in the field of animal behaviour. Currently, dominance hierarchies are viewed as complex social structures formed by repeated interactions between individuals. Most studies on this phenomenon come from single-species groups. However, animals are constantly surrounded by and interact with individuals of other species. Behaviour and social interactions of individuals can be shaped by the presence or behaviour of other species in their social ecosystem, which has important implications for social behaviour in groups. Given how ubiquitous mixed-species animal groups are, deeper study of the relationships between mixed-species group (MSG) structure and dominance will be key to understanding constraints on individual behaviour and decision making. Here we call for more research into dominance interactions among individuals in MSGs. Greater understanding of the dynamics of dominance relationships among individuals in MSGs, whose size and composition can change considerably over shorter and longer term time frames, will be crucial to understanding their structure and functioning. This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’.

Signalers can vary their vocal behavior, depending on the presence or absence of conspecific group members, and on the composition of the group. Here we asked whether Carolina chickadee () signalers varied their vocal behavior, depending on whether they were in the presence of familiar or unfamiliar flockmates. We sorted 32 Carolina chickadees into 4 groups with 4 familiar birds each and 4 groups with 4 unfamiliar birds each and recorded their behavior in seminatural aviary settings. We presented the familiar and unfamiliar aviary groups with a variety of stimuli ranging in level of threat and assessed birds' calling behavior in these contexts. Birds housed with familiar flockmates called sooner in threatening stimulus presentations compared with birds housed with unfamiliar flockmates. Call rates and note compositions of calls produced did not differ for the 2 types of flock. Upon release from the captive aviaries, birds from familiar flocks were also more likely to call in flight than were birds from unfamiliar aviaries. These findings suggest that chickadees vary their calling behavior as a function of experience with their surrounding social audience and provide insight into mechanisms of flock cohesion and relationship formation and maintenance within flocks. (PsycINFO Database Record

Individuals of a wide range of species are sensitive to the presence of other species, and can often benefit from associations with other species in mixed-species groups (MSGs) through food-finding or avoiding predation. In an earlier field study, we found that both Carolina chickadees, Poecile carolinensis, and tufted titmice, Baeolphus bicolor , were better able to solve a novel feeder task when their MSGs were more diverse in terms of species composition. Like most studies of MSGs, however, that earlier study did not experimentally manipulate MSG size and composition. We did that manipulation here, providing experimental flocks of chickadees and titmice with three novel feeder tasks in semi-natural aviary environments. We found that successful titmouse flocks generally had a higher proportion of titmice in them, going against the findings of our earlier field study. Conversely, successful chickadee flocks solved one of the novel feeder tasks more quickly with a higher proportion of titmice in them, corroborating the findings of our earlier field study. We now need to assess socio-ecological influences on MSG size and composition, and how those relate to individual behaviour. This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’.

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