Tracking deer using only sound

In national parks throughout Japan, park rangers are faced with the daunting and time-consuming task of tracking deer populations. Deer are not native to these ecosystems, and can have damaging effects if they are not monitored and controlled. 

In a new study, experts at the University of Tokyo have developed a new technique for tracking deer movements using unmanned listening devices.

“Determining deer position enables the elimination of repetitive calls from the same deer, thus providing a promising tool to track deer movement,” explained the researchers. “The validation results revealed that the proposed technique can provide reasonable accuracy for the experimental and natural environment.”

The technology could soon take the place of current methods of monitoring deer populations, which range from counting droppings to using images from trail cameras.

“The problem with using recording devices to estimate the size of deer populations in the past was that it was difficult to avoid counting the same deer multiple times – by setting up a grid of listening stations, we are able to triangulate the position of each deer with precision and track its movements,” explained study co-author Tadanobu Okumura.

The researchers built a prototype listening station which is powered by solar panels and automatically synchronizes its internal clock with a GPS satellite. The recordings can be used to determine the precise location of deer based on a triangulation technique.

“When we tested our prototype in an experimental setting in the playground of the University of Tokyo, we were able to pinpoint the location of a sound within five meters. In a second trial under more realistic conditions in the marshland at Oze National Park, it was possible to locate a sound to within about fifteen meters,” said study co-author Kazuo Oki. During a two-hour trial, the system picked up 72 distinct deer calls. 

“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,” wrote the study authors. 

“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.”

The research is published in the journal Sensors.

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By Chrissy Sexton, Earth.com Staff Writer