Aggression and multimodal signaling in noise in a common urban songbird

Abstract

The effect on anthropogenic noise on acoustic signals is widely studied although the extent to which this is due to short-term flexibility or long-term adaptation is unclear. Anthropogenic noise may disrupt signals used to mediate aggressive interactions, leading to more physical aggression between opponents. One solution to this problem is to switch signaling effort to a less noisy modality (e.g. the visual modality). In the present study we ask whether urban and rural European robins (Erithacus rubecula) use multi-modal signals flexibly in response to anthropogenic noise during territorial defense. We predicted that during simulated intrusions with experimental noise, European robins would increase their physical aggression, respond with more visual threat displays and sing fewer songs, i.e. show a multi-modal shift. We also predicted that urban birds, living in noisier habitats, would be generally more aggressive than rural birds. The results showed that urban birds were more aggressive than rural robins, but an increase in aggression with experimental noise was seen only in the rural birds. Urban birds also used visual signals more often than rural birds. However, birds did not use visual signals more in experimental noise. Instead, both urban and rural robins sang at higher rates under noise conditions, thus increasing signaling effort in the noisy modality. These results point to a complex role of immediate plasticity and longer-term processes in affecting communication during aggressive interactions under anthropogenic noise.Significance StatementHuman activity has an enormous effect on wildlife, including on their social behavior. Animals living in urban areas often tend to be more aggressive than those living in rural areas, which may be due to urban acoustic noise making communication between individuals more difficult. In a study with a common songbird, the European robin, we investigated the role of urban acoustic noise in aggression and territorial communication. Urban robins were more aggressive than rural robins, and additional noise in the territory increased aggression in rural but not urban robins. Robins increased their singing effort but did not increase visual signals in acoustic noise. These results suggest that noise can indeed make animals behave more aggressively although the effect may depend on how noisy it is already. These results further our understanding of how human-made noise changes animal communication and social behavior.

How Are Urban Birds Affected by Surrounding Forests and Agricultural Landscapes?

“…In certain parts of Europe, the European Robin is commonly observed in anthropogenic landscapes and is considered an urban species [82]. Recent studies have analyzed the species' adaptation and behavioral changes in urbanized areas [80][81][82][83][84][85]. In Lithuania, the European Robin is a migratory species that rarely or occasionally winters.…”

Communication breakdown! Signal modality drives the effect of information loss on the behavioral responses of the threatened Great-Billed Seed-Finch, Sporophila maximiliani (Thraupidae: Passeriformes)

“…Also, we expected that ii) aggressiveness would be readily used as a coping strategy, as we are simulating a territory dispute. Aggressiveness is a common behavior for territorial birds in contexts where the risk assessment is di cult (Onsal et al 2022). To territorial owners, the cost of losing the territory in dispute is larger and the aggressiveness would be the most e cient coping strategy without an accurate evaluation of its competitor (Furtado and Nomura 2014) (Figure 1).…”

Communication breakdown! How information loss affects behavioral responses in the Great-Billed Seed-Finch, Sporophila maximiliani (Thraupidae: Passeriformes)

“…Thus, the motivational con ict would be greater in partial information contexts, since the context of either total information or little information (strong degradation) would result in lower ambiguity for the receiver to interpret. Also, we expected that ii) aggressiveness would be a common behavior for territorial birds in contexts where the risk assessment is di cult (Onsal et al 2022). To territorial owners, the cost of losing the territory in dispute is larger and the aggressiveness would be the most e cient coping strategy without an accurate evaluation of its competitor (Furtado and Nomura 2014).…”