Radio-tagging and Monitoring

by Pat Leonard last modified 2007-04-19 16:44

A High-Tech Game of Tag


The Bioacoustics Research Program (BRP) helps researchers listen in on the world’s creatures, track their movements, and decipher what animal sounds and behaviors mean. A group of creative BRP design engineers develops the cutting-edge radio frequency (RF) hardware needed to make this possible for studies on everything from Arctic whales to African elephants.

“We’re on the brink of an animal tracking revolution,” says BRP design engineer Rob MacCurdy. “We’re doing things that people have not chosen to do and we’re doing them on a scale that’s appropriate for biologists and for small organizations.” The technology is an integral part of scientific studies taking place at the Cornell Lab of Ornithology. Lab scientist Dr. Alejandro Purgue is the principal investigator on all the radio frequency projects. “My first interest is science," he says. "I do engineering not as an end in itself but because the biological questions I want to answer cannot be answered with existing technology.”

Gizmos and Gadgets

Among the devices already designed, tested, and put into service by the design group are the workhorses of the Bioacoustics Research Program: underwater recorders called pop-ups and their land-based cousins, the autonomous recording units (ARUs).

Pop-ups are anchored to the ocean floor to record the sounds of marine mammals within a pre-set range of frequencies. When the hard drive is full, a signal is sent to the device to cut loose from its tether and “pop-up” to the surface. A radio frequency transmitter then sends out a signal that allows scientists to find and retrieve the device. Pop-ups are used in monitoring North Atlantic right whales and in other marine projects.

ARUs do the job on land. A length of PVC tubing houses the hard drive and electronics. A microphone array is attached to one end, covered by a windscreen. The latest incarnation of these devices allows users to program when they record and for how long. ARUs may be left in the field for two weeks or more before the information is downloaded. The recordings can then be screened and turned into spectrograms for analysis. This technology is used in the ongoing search for the Ivory-billed Woodpecker.

Building Better Mousetraps

The RF design group is now hard at work on two exciting grant-funded projects, both of which address specific problems in remote and long-distance animal monitoring.

Moore Foundation Project

Researchers scanning the horizon with metal antennas to pick up radio signals from tagged animals are a familiar sight in television nature shows. For more than 60 years, there has been little improvement to this cumbersome and time-consuming tracking method. Thanks to a grant from the Moore Foundation, the RF group is creating an automated system of receivers and transmitters that can do the job quickly, accurately, and much more easily. Design engineer Rich Gabrielson is one of those designing the new system. He says, “We’re using GPS technology with more accurate time-stamping as well as smaller, more powerful computer chips for transmitting and processing information. These are recent innovations that are making our design possible now.”

An animal is fitted with a radio collar and antenna. The collar contains a battery and a tag designed by the BRP engineers. The tag (left) is essentially a mini-computer that emits amplified radio-frequency signals. The most innovative part of the project is the receiver array (below). Each receiver looks like a metal suitcase on tripod. Three or more are set up in an area of study, usually on high ground. Each precisely measures the time it detects a signal from the animal’s collar and shares that information with the other receivers. Because the animal is a different distance from each receiver, the signal from its collar will arrive at a different time for each one. From
those differences in time of arrival, the exact position of the animal can be calculated to within a radius of 200 meters. The receivers are also about 10 times more sensitive than traditional receivers, extending the range over which they can “hear” a transmitting collar and allowing for tracking in real time. This system will be field tested on jaguars in Peru. When the system is ready for prime time, the technology will be made available to everyone.

National Science Foundation Mini-Tagging Project

Another challenge for scientists is tracking small animals over long distances, especially birds. A National Science Foundation grant is funding the development of lighter, smarter tags that smaller birds and animals can carry.

The tags being used now do not do much more than transmit. Lab scientist Alejandro Purgue says, “Our mini-tags have a built-in computer that can be programmed to gather data at specific times. They can also store information and share data with tags on nearby animals.” Currently, tags transmit on a pre-set schedule regardless of whether anyone is listening. The mini-tags are silent and only transmit when they are being queried by a transmitter in range—so there are no idle transmissions. “This saves a lot of power,” Purgue says, “It extends life of the unit, and allows the use of a smaller battery.”

The new tags also have a light sensor built in. Based on light levels, they establish the time of sunrise, midday, and sunset. With those three data points the tags log the position of the animal. While a bird migrates, this position data is being stored in memory. When the bird returns to the tagging site, the data is downloaded and scientists have a day-by-day log of the bird’s travels. Data could also be downloaded at points along the bird’s journey via receiver units set up to query the bird’s tag, download the data, and store it locally. A program to analyze the data downloaded from the mini-tag will also be developed by Dr. Purgue, converting files of times into geographical positions.

A prototype system was ready at the end of 2006. Dr. Purgue will be there when it is deployed by the Netherlands Institute of Oceanographic Research (NIOZ) to study Red Knots flying from Africa, over Germany, on to Siberia. It’s likely some version of this technology will be used for his primary area of interest, whale tagging. In this case, the stored position data would be uploaded to a tag on a passing bird perhaps, and downloaded by a scientist on shore when the bird comes within range—rather like a cell phone call skipping from cell to cell to get to its final destination. Whales stay too far from shore to make a direct tag query feasible—at least for now.

The Greater Good

In the past researchers have only been able to track one animal at a time and collect sporadic information about where it went. The work being done by the RF group will help advance understanding about how much land animals actually need, what areas of the earth they are using, and what impact humans may have when they disturb habitats. Armed with that data, leaders can make informed decisions about how land will be managed. “There are lots of places where you can do interesting engineering work,” says Rob MacCurdy, “But very few places where you can do interesting engineering work and have a real impact on animal conservation.”