Mobbing miners

Submitted by Michi on 8 July 2024.

Photo above: noisy miners mobbing (Photo Credit: Paul McDonald).

Text by Julie Kern

Mobbing in noisy miners may be more selective than previously thought, with caller familiarity and location both influencing this behaviour, according to new experimental research by Julie Kern and Paul McDonald at the School of Environmental and Rural Science, University of New England (UNE), Australia.

Many bird species engage in mobbing, approaching, harassing, and even physically attacking a threat. Surely in the running for the title of ‘most successful mobber’ is the noisy miner, a honeyeater native to south-eastern Australia where it lives in colonies of up to several hundred individuals. Indeed, noisy miners are so successful when it comes to mobbing, that this behaviour is listed as a ‘Key Threatening Process’ under Australia’s federal biodiversity laws. Noisy miner mobbing has been described as despotic behaviour due to the number of birds that participate in mobbing, the persistence of it, and the wide variety of other birds that are mobbed (not just predators). Whilst numerous studies have identified the damage to woodland-bird biodiversity caused by noisy miner mobbing, however, less is known about mobbing itself, including which factors influence the decision of whether to mob or not.

                                          Group corroboree (congregation display) following a mobbing event (Photo Credit: Paul McDonald).

In this study, Julie and Paul investigated group mobbing behaviour in noisy miners, asking whether mobbing responses varied in relation to colony borders and caller familiarity. They conducted field-based experiments at a colony of noisy miners near UNE’s Armidale campus. After recording their mobbing vocalisations (known as ‘chur calls’), these were broadcasted both inside and outside of colony borders. Noisy miners heard calls from both familiar birds (members of their own colony) and unfamiliar birds (members of a distant colony).

                                                    Observation hide for playback experiments (Photo Credit: Julie Kern)

Noisy miners were more likely to respond, reacted more quickly and responded more strongly to chur calls broadcast inside as opposed to outside the colony, probably because of variation in the costs and benefits of responding. Inside the colony, the benefits are obvious, driving out predators and resource competitors from their colony. Outside, however, such benefits may no longer offset potential costs – colony borders generally mirror vegetation, excluding open habitat where miners may be more at risk of predation. When noisy miners did mob outside the colony, more individuals joined in response to unfamiliar as opposed to familiar callers. This suggests that noisy miners use identity-related information, known to be encoded in their chur calls from some of Paul McDonald’s earlier work.  

Given the strong interest in noisy-miner management, the authors suggest that future behavioural work needs to consider mobbing behaviour in more detail, asking questions applicable to management. For example, the question of how far beyond colony borders mobbing extends remains untested. The answer will inform the size and placement of vegetation corridors that link patches of woodland but increases the threat from noisy minor mobbing to avian biodiversity.

To combat the adverse effects of noisy miner mobbing to the broader avian community we need to develop a deeper understanding of noisy miner mobbing behaviour itself, and this study is an important step in that direction.

Link to paper. 

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