Behavioural plasticity shapes participation in a mixed-species flocking community of birds

Behavioural plasticity can modulate the costs and benefits of sociality and thus may play a prominent role in mediating competition and facilitation during social interactions in mixed-species groups. However, investigations of assembly patterns of mixed-species groups typically treat species' behavioural attributes as static rather than dynamic features that can change in social contexts. We investigate four axes of behavioural plasticity that may modulate interactions within mixed-species groups: (1) species' selective preference for joining certain groups, (2) species' ability to flexibly change their behaviour in response to groupmates' behaviour and (3) shifts and/or (4) flexibility of species' niche breadth resulting in either shrinking or expansion when foraging with conspecifics versus when foraging with heterospecifics. We assess variation in these axes of behavioural plasticity in an Australian mixed-species avian community. All species had selective preferences for flocks of certain strata, and some flexibly matched their flockmates' foraging strata. Three species exhibited patterns of niche shift, and one species showed niche expansion. These findings suggest that species converge in strata in mixed-species flocks despite the potential for increased competition and emphasize that species can plastically react to changes in their social environment in numerous ways. Acknowledgment of such plasticity is likely integral to understanding the nuances of heterospecific interactions.