Grey-headed flying-foxes in an urban environment disrupted by noise.

Silent Skies: How Urban Noise Impacts Flying-Fox Communication—and What We Can Do

Avery Sinclair in Climate & Environment August 2025 • 5 min read.

"Discover the surprising ways city sounds affect these vital creatures and explore the simple steps we can take to protect their connection."

Imagine a world where the sounds you rely on to connect with others are constantly drowned out by the clamor of the city. This is the reality for many grey-headed flying-foxes, a highly vocal species increasingly making their homes in urban environments. As human populations expand, encroaching on wildlife habitats, the noise we create significantly impacts animal behavior. It’s not just about being a nuisance; it's about disrupting essential communications.

These amazing creatures, native to the rainforests and woodlands of eastern Australia, are now frequently found in urban areas due to habitat loss and the availability of alternative food sources. In cities, they face many challenges, one of the most pervasive being noise pollution. Noise can mask important acoustic signals, affecting how they communicate, find mates, and avoid danger. Think about how difficult it is to have a conversation in a crowded, noisy room—now imagine that's your everyday environment.

A recent study investigated the effects of urban noise on the communication behavior of grey-headed flying-foxes, focusing on how these animals adjust their vocalizations in response to varying levels of environmental noise. The research sought to understand whether urban noise affects the acoustic structure of their calls and if these animals are conforming to what’s known as the 'ultimate level hypothesis,' where they call to one another at maximum power levels, regardless of the surrounding noise.

Decoding the Sounds of Silence: Understanding the Silentium Effect

Grey-headed flying-foxes in an urban environment disrupted by noise.

The researchers explored whether there were differences in the acoustic structure of flying-fox calls between rural roosts (lower environmental noise) and urban roosts (higher environmental noise). To do this, they recorded and compared sound pressure levels and dominant frequencies of colony sounds across a gradient from highly rural to highly urban roosts. They also analyzed the signal structure of individual flying-fox calls to see if the bats were changing how they communicate.

Interestingly, the study found no significant differences in the colony soundscapes regarding amplitude or the dominant frequency of flying-fox vocalizations across the different roosts. This means that whether the bats were in a quiet rural area or a bustling urban center, the overall sound levels and frequencies of their calls remained relatively consistent. Similarly, there were no notable differences in the dominant frequency or syllable rate of individual courtship brays (a type of vocalization used during mating rituals) between highly rural and highly urban roosts.

Consistent Vocalizations: Regardless of the environment, the basic characteristics of their calls remained the same.
No Change in Courtship Calls: The mating calls didn't change in frequency or rate, whether in quiet or noisy areas.

However, the researchers uncovered a fascinating behavior: the flying-foxes temporarily stopped vocalizing when low aircraft flyovers caused environmental noise levels to spike dramatically. This cessation of vocalizing in response to high levels of anthropogenic noise was termed the 'silentium effect.' This behavior has been observed in other species, such as cetaceans and anurans, indicating a potential widespread strategy for coping with extreme noise.

Looking Ahead: Protecting the Soundscapes of Our Shared Environments

While the study indicates that current typical urban noise levels do not appear to alter the acoustic structure of grey-headed flying-fox bray vocalizations, the 'silentium effect' raises concerns about the potential impacts of extremely high noise levels, such as those from airline traffic. By understanding how noise pollution affects these animals, we can work towards creating quieter, more sustainable urban environments where both humans and wildlife can thrive. Simple steps, such as supporting policies that reduce urban noise and being mindful of our own noise footprint, can make a significant difference.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1007/s11252-018-0814-2, Alternate LINK

Title: Urban Noise And Grey-Headed Flying-Fox Vocalisations: Evidence Of The Silentium Effect

Subject: Urban Studies

Journal: Urban Ecosystems

Publisher: Springer Science and Business Media LLC

Authors: Tim Pearson, Jennifer A. Clarke

Published: 2018-11-06

Everything You Need To Know

What specific challenges do grey-headed flying-foxes face in urban environments due to noise?

Grey-headed flying-foxes in urban environments experience significant challenges due to noise pollution. This noise masks acoustic signals, hindering their ability to communicate, find mates, and avoid danger. The constant clamor of the city disrupts their essential communications, impacting their daily lives and behaviors within these environments. This can affect their ability to coordinate activities and maintain social structures.

What is the 'silentium effect' observed in grey-headed flying-foxes, and why is it significant?

The 'silentium effect' refers to the temporary cessation of vocalizations by grey-headed flying-foxes in response to extremely high levels of noise, particularly from low aircraft flyovers. This behavior is significant because it indicates that these animals are actively responding to and coping with extreme noise pollution. It highlights their vulnerability to anthropogenic noise and suggests that while typical urban noise might not alter their vocal structures, sudden, intense noise events can disrupt their communication, potentially affecting their behavior and survival.

How did the researchers investigate the impact of noise on grey-headed flying-fox communication, and what were the main findings?

The researchers investigated the effects of urban noise on the communication behavior of grey-headed flying-foxes by comparing the acoustic structure of their calls in rural (lower noise) and urban (higher noise) roosts. They analyzed sound pressure levels, dominant frequencies, and individual call characteristics. The study found no significant differences in overall sound levels or frequencies of their calls between different roosts. Similarly, the dominant frequency or syllable rate of individual courtship brays did not show notable differences between rural and urban environments. The main finding was the 'silentium effect', where the flying-foxes temporarily stopped vocalizing during low aircraft flyovers.

What are the implications of the study's findings for the conservation of grey-headed flying-foxes in urban areas?

The study's findings have several implications for the conservation of grey-headed flying-foxes in urban areas. While typical urban noise may not significantly alter their vocalizations, the 'silentium effect' indicates a vulnerability to extreme noise events. This highlights the need for policies that reduce noise pollution in urban environments, particularly from sources like aircraft. Creating quieter urban spaces can help protect these vital creatures and allow both humans and wildlife to thrive, ensuring these animals can communicate effectively and maintain their essential behaviors.

What practical steps can be taken to help protect the communication of grey-headed flying-foxes from urban noise pollution?

Several practical steps can be taken to protect the communication of grey-headed flying-foxes from urban noise pollution. Supporting policies that reduce urban noise is crucial. This includes advocating for noise reduction measures in city planning and transportation. Being mindful of our noise footprint by reducing unnecessary noise in our daily lives, like traffic and loud activities near habitats of the grey-headed flying-foxes, can also make a difference. These simple steps can create quieter, more sustainable environments, allowing the grey-headed flying-foxes to thrive and communicate effectively.