Location and caller familiarity influence mobbing behaviour and the likely ecological impact of noisy miners around colony edges

Mobbing is a widespread, vocally coordinated behaviour where species approach and harass a threat. The noisy miner (Manorina melanocephala) is a notorious native Australian honeyeater, well-known for its hyperaggressive mobbing. Numerous studies have identified negative impacts of their mobbing behaviour, highlighting the exclusion of competitors from colony areas and the resulting loss of woodland-bird biodiversity. Despite this, few studies have investigated mobbing itself, and our understanding of the factors which influence its expression remains limited. Here, we use a field-based playback experiment to investigate whether mobbing responses vary in relation to colony borders and caller familiarity. Noisy miners were more likely to respond, reacted more quickly and responded more strongly to mobbing calls broadcast inside as opposed to outside the colony. These behavioural differences likely arise from variation in the relative costs and benefits of responding. When noisy miners did mob outside the colony, more individuals joined in response to unfamiliar as opposed to familiar callers. Our results reveal that noisy miner mobbing may not be as indiscriminate as often assumed, with caller familiarity and location influencing this behaviour. We suggest there are benefits to greater consideration of the factors impacting noisy miner mobbing behaviour.