Acoustic Ecology in Birds: How to Avoid Danger in Noisy and Cluttered Environments

Abstract

Information is crucial in predator-prey interactions, yet can be difficult to obtain in complex environments. Sounds, such as alarm calls and direct sounds from predators, are an important source of information for animals assessing the potential risk about the surroundings. However, acoustic information can be disrupted by anthropogenic and other noises, a growing concern due to increasing global noise levels. Furthermore, acoustic information becomes even more valuable in cluttered environments where predators may be visually hidden. Therefore, to avoid predation, animals need to be flexible, gaining information from various sources and actively minimising information available to predators. My PhD research focused on how birds handle acoustic information related to danger in acoustically or visually restricted environments.

The thesis is divided to two main sections. First, I investigated the challenge of noise on bird acoustic communication, using superb fairy-wrens (Malurus cyaneus) as a model species. Many studies show that noise can disrupt acoustic communication, but rarely know the mechanism. I therefore explored how noise disrupts communication, even when noise occurs before or after a signal. I found masking was the mechanism that stopped fairy-wrens responding to alarm calls, but noise before or after the alarm calls was unlikely to affect fairy-wrens fleeing. Second, I examined the challenge of information use by white-browed scrubwrens (Sericornis frontalis) during incubation, a period typically ignored in studies of communication. Scrubwren nests are extremely cryptic, and so difficult for predators to find, but this also means that incubating birds have a very restricted view outside the nest, that leaves them vulnerable to predator approach. I found that incubating scrubwrens assessed acoustic information of danger at nests, and used a specific call, which had never been described acoustically, to signal group members to stay away from the nest and so help maintain nest crypsis.

Overall, my research underscores the crucial role of acoustic information in predator detection and survival strategies for birds, particularly in noisy and visually restricted environments. By examining noise mechanisms, this work contributes to predicting and potentially mitigating the impacts of noise pollution on avian behaviour. Studies on scrubwrens highlight the adaptability of birds in using vocalisations to communicate about danger while maintaining nest concealment. This research emphasises the importance of understanding animal communication to support conservation in increasingly complex and changing habitats. Show more