Forest Elephants Passive Acoustic Monitoring

Forest elephants are rapidly disappearing, with over 60% lost in the past decade and more than 12,000 killed annually for their ivory. Despite these alarming statistics, there is hope for their survival through immediate action.

A critical challenge in conserving forest elephants is the lack of essential data. We currently have insufficient knowledge about where elephant populations are located over time and space, as well as inadequate data on patterns of poaching. These gaps are crucial for developing effective conservation and anti-poaching strategies, especially in the expansive forests of Central Africa where prioritizing protection is essential.

Our vision is to conserve the tropical forests of Africa through acoustic monitoring, sound science, and education, focusing on forest elephants

– The Elephant Listening Project

Vital Roles of Forest Elephants in Ecosystems

Forest elephants of Africa play a crucial role in maintaining the health and balance of their ecosystems. Here are several reasons why they are vital:

• Seed Dispersal: Forest elephants are key seed dispersers. They consume a variety of fruits and plants, and their movement through the forest helps in spreading seeds over large areas. This promotes forest regeneration and diversity, ensuring the survival of many plant species.
• Habitat Modification: As they move through the forest, forest elephants create clearings and pathways. This behavior helps in maintaining a mosaic of different habitats, which supports a variety of plant and animal species. Their foraging activities also prevent any single species from becoming too dominant, thus maintaining ecological balance.
• Nutrient Cycling: By feeding on various plants and depositing dung, forest elephants help recycle nutrients within the forest ecosystem. Their dung is rich in nutrients and serves as a fertilizer, enhancing soil fertility and promoting plant growth. It also provides food for a range of other organisms, including insects and fungi.
• Water Distribution: Forest elephants often dig for water in dry riverbeds, creating water holes that are crucial for many other species during dry periods. These water sources are vital for the survival of numerous animals and help sustain the biodiversity of the forest.
• Biodiversity Support: The presence of forest elephants supports a wide range of biodiversity. By maintaining diverse and dynamic habitats, they provide the necessary conditions for various plant and animal species to thrive. This biodiversity is essential for ecosystem resilience and stability.
• Climate Regulation: Forests where elephants live are important carbon sinks. By promoting forest growth and regeneration through their activities, elephants help in sequestering carbon dioxide, thus playing a role in mitigating climate change.

In summary, forest elephants are ecosystem engineers whose activities support the structure, function, and biodiversity of their habitats. Their conservation is not only crucial for their survival but also for the health of the entire ecosystem they inhabit.

Conservation Threats to Forest Elephants

Forest elephants face significant threats that challenge their survival and conservation efforts. In addition to the widespread issues of poaching for ivory and habitat loss, these elephants are increasingly pressured by hunting for meat, accelerating natural resource extraction, and a lack of development in ecotourism that could provide alternative economic value. Combined with their slow reproductive rate, these factors create immense challenges for conservation.

We have lost 60% of all forest elephants in the past decade

– The Elephant Listening Project

Ivory Poaching

Forest elephant ivory is highly prized, particularly for its hardness and distinctive rose-colored tint, making it ideal for carving and demanding higher prices in the marketplace. This preference is especially strong in Japan, where “harder” ivory has dominated the trade for decades. Premium quality bachi, traditional Japanese plucking tools for the shamisen, are made exclusively from forest elephant tusks.

Gallery / basket of rhino horns left next to a pyre of burning elephant ivory in Kenya, 2016. Photo credit to Ben Curtis, AP

Poaching is particularly difficult to detect in the dense rainforests of Central Africa. Most estimates of poaching levels come from ivory seizures at ports, which have been increasing. As anti-poaching efforts in East and Southern Africa become more effective, Central Africa’s sparsely populated and poorly protected forests have become more attractive to organized poachers. However, improved anti-poaching systems in places like Nouabalé-Ndoki National Park in Congo are beginning to show positive results, with more poachers being successfully prosecuted.

Bushmeat Trade

Ivory is not the only driver of forest elephant poaching. The bushmeat trade has become an international business, with markets for African rainforest animals extending to major cities in the U.S. Hunting forest elephants for bushmeat is on the rise, posing a grave threat to elephants of all ages, including calves. Local economies often rely on bushmeat for protein, but growing human populations have made this practice unsustainable. Efforts to reduce the bushmeat trade include establishing checkpoints on major roads and key railroad stations to disrupt commercial networks and control vehicle access to remote areas.

Natural Resource Extraction

The extraction of natural resources such as wood, minerals, and oil poses severe threats to forest elephants. Logging is currently the most pervasive industry, with selective logging often creating small openings that can benefit forest elephants by promoting new vegetation growth. However, the construction of roads for resource extraction increases access for hunters and the number of people living in the forest. The demand for sustainable wood products has led to improvements, such as internationally recognized certification for large companies, but these measures do not yet include requirements to close roads and monitor access by private vehicles.

Elephant Rumbles

Elephant rumbles are low-frequency vocalizations produced by elephants, primarily for communication.

Gallery / Spectrogram of elephant rumbles

These rumbles are a fundamental part of elephant social interactions and serve various purposes within their groups. Here’s a detailed explanation:

Characteristics of Elephant Rumbles

• Low Frequency: Elephant rumbles typically fall in the infrasound range, below 20 Hz, which is often below the threshold of human hearing. However, some rumbles can also be heard by humans as a low, throaty sound.
• Long Distance Communication: Due to their low frequency, rumbles can travel long distances, sometimes several kilometers, allowing elephants to communicate with each other across vast areas, even when they are out of sight. It can also travel through dense forests as the wavelength is very large.
• Vocal Production: Rumbles are produced by the larynx and can vary in frequency, duration, and modulation. Elephants use different types of rumbles to convey different messages.

Functions of Elephant Rumbles

• Coordination and Social Bonding: Elephants use rumbles to maintain contact with members of their herd, coordinate movements, and reinforce social bonds. For example, a matriarch might use a rumble to lead her group to a new location.
• Reproductive Communication: Male elephants, or bulls, use rumbles to communicate their reproductive status and readiness to mate. Females also use rumbles to signal their estrus status to potential mates.
• Alarm and Distress Calls: Rumbles can signal alarm or distress, warning other elephants of potential danger. These rumbles can mobilize the herd and prompt protective behavior.
• Mother-Calf Communication: Mothers and calves use rumbles to stay in contact, especially when they are separated. Calves may rumble to signal hunger or distress, prompting a response from their mothers.

Importance of Understanding Elephant Rumbles

• Conservation Efforts: Understanding elephant communication helps in conservation efforts by providing insights into their social structure, habitat needs, and responses to environmental changes.
• Human-Elephant Conflict Mitigation: By recognizing alarm rumbles, conservationists can better manage and mitigate conflicts between humans and elephants, especially in regions where their habitats overlap.
• Enhancing Animal Welfare: For elephants in captivity, understanding their rumbles can help caretakers improve their welfare by addressing their social and environmental needs more effectively.

Overall, elephant rumbles are a vital aspect of their complex communication system, reflecting the sophistication of their social interactions and the importance of acoustic signals in their daily lives.

Project Scope and Objectives

Fifty microphones are arranged in a grid within the Tropical Forest of Central Africa, continuously recording forest sounds around the clock. The collaboration aims at developing an advanced sound analyzer capable of processing these extensive audio recordings at high speed, allowing for the analysis of terabytes of audio data in just a few days. Making it possible to automatically detect and localize elephant rumbles from the large amount of audio data.

An audio analyzer capable of automatically detecting elephant rumbles can significantly enhance conservation efforts for forest elephants. Here are several key benefits:

Improved Monitoring and Data Collection

• Continuous Surveillance: An audio analyzer can operate 24/7, providing continuous monitoring of elephant populations. This is especially useful in the dense and often inaccessible rainforests of Central Africa.
• Non-Invasive Tracking: Unlike traditional tracking methods, audio monitoring is non-invasive and does not disturb the elephants or their natural behaviors.

Enhanced Understanding of Elephant Behavior

• Behavioral Insights: Detecting and analyzing rumbles can provide insights into elephant communication, social structures, and movement patterns.
• Stress and Distress Signals: By recognizing specific types of rumbles, conservationists can identify signs of stress or distress, potentially indicating threats such as poaching or human-elephant conflicts.

Anti-Poaching Efforts

• Real-Time Alerts: An audio analyzer can send real-time alerts when elephant rumbles are detected, enabling rapid response to potential poaching activities.
• Poaching Hotspot Identification: By analyzing data over time, it is possible to identify patterns and hotspots of poaching activity, allowing for more targeted and effective anti-poaching strategies.

Habitat Usage and Movement Patterns

• Spatial Analysis: Understanding where and when elephants are active can help in mapping their habitats and migration routes.
• Resource Management: This information is crucial for managing protected areas, ensuring that resources are allocated effectively to areas where elephants are most vulnerable.

Developed tools

Open source tools were developed during this project to process large amounts of audio data in batch, leveraging multiprocessing to localize forest elephant rumbles with high accuracy. The aim is to enable rapid analysis of large-scale audio datasets, potentially reaching terabyte scales, by optimizing processing speed and efficiency through the use of maximum CPU and GPU cores. Benchmark analyses show that processing a 24-hour audio file on an 8-core CPU takes approximately 35 seconds, while using a GPU (T4) and an 8-core CPU reduces the time to approximately 20 seconds.

Spectrogram	Prediction

Analyzing months of audio recordings can now be done in a matter of hours, not weeks!

Analyzing 1TB of data - approximately 1 month of audio recordings for the 50 recorders - would require 14.6 hours with CPUs, but only 8.3 hours using the GPU and CPU cores.

Conclusion

In summary, an audio analyzer that detects elephant rumbles offers numerous advantages for the conservation of forest elephants. It provides continuous, non-invasive monitoring, enhances our understanding of elephant behavior, aids in anti-poaching efforts, informs habitat management, supports research, engages local communities, and offers a cost-effective, scalable solution for conservation efforts.

One can try out the model from the ML Space or directly from the snippet below: