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.