Detecting and Tracking the Positions of Wild Ungulates Using Sound Recordings.

Salem Ibrahim Salem,Kazuo Oki,Kazuhiko Fujisao,Tadanobu Okumura,Masayasu Maki

doi:10.3390/s21030866

Abstract

Monitoring wild ungulates such as deer is a highly challenging issue faced by wildlife managers. Wild ungulates are increasing in number worldwide, causing damage to ecosystems. For effective management, the precise estimation of their population size and habitat is essential. Conventional methods used to estimate the population density of wild ungulates, such as the light census survey, are time-consuming with low accuracy and difficult to implement in harsh environments like muddy wetlands. On the other hand, unmanned aerial vehicles are difficult to use in areas with dense tree cover. Although the passive acoustic monitoring of animal sounds is commonly used to evaluate their diversity, the potential for detecting animal positions from their sound has not been sufficiently investigated. This study introduces a new technique for detecting and tracking deer position in the wild using sound recordings. The technique relies on the time lag among three recorders to estimate the position. A sound recording system was also developed to overcome the time drift problem in the internal clock of recorders, by receiving time information from GPS satellites. Determining deer position enables the elimination of repetitive calls from the same deer, thus providing a promising tool to track deer movement. The validation results revealed that the proposed technique can provide reasonable accuracy for the experimental and natural environment. The identification of deer calls in Oze National Park over a period of two hours emphasizes the great potential of the proposed technique to detect repetitive deer calls, and track deer movement. Hence, the technique is the first step toward designing an automated system for estimating the population of deer or other vocal animals using sound recordings.

Highlights

Camera traps that are automatically triggered by movement have been used to monitor the density of various wildlife animals such as American marten (Martes americana) [10], livestock [11], and wild ungulates [12,13] to evaluate their impact on the surrounding environment [14,15]
This study introduces a new sound-based technique to estimate deer’s position based on sound recordings of deer calls at three stationary recorders
The sound editor windows of Praat (Figure 5a–c) illustrate the characteristics of the sound recorded by the three recorders when the deer whistle was used at point E (Figure 5d)

Summary

Introduction

National Park [6] in Japan, resulting in irreversible effects on the original ecosystem such as destruction of rare plant species [7]. Monitoring the population dynamics of deer is crucial for the effective evaluation and management of ecosystems [8]. The light-census survey is strongly influenced by weather conditions, deer movements, and accessibility of the location, which causes considerable uncertainty in the observed data. Camera traps that are automatically triggered by movement have been used to monitor the density of various wildlife animals such as American marten (Martes americana) [10], livestock [11], and wild ungulates [12,13] to evaluate their impact on the surrounding environment [14,15]. Thermal cameras have been used to automatically detect animals in a grassland habitat [16]

Methods

Results

Conclusion