For the past three summers, I have worked on a Flat-Tailed Horned Lizard (Phrynosoma mcallii) Reproduction project. Our objectives were to determine behavior and movement of gravid female lizards. It is difficult to reliably find the same individual by following tracks in the sand, as lizards may not be out or in the same area anymore. Instead, we use radio telemetry to follow, monitor, and relocate individuals multiple times per day. Radio telemetry is one of my favorite things to do because it allows us to learn about a species’ behavior, life history, movement patterns, and habitat use at the same time.
Radio telemetry requires three pieces of equipment: a transmitter, an antenna, and a receiver. The transmitter is attached to an individual animal, which in our study was glued to the dorsal side of the lizard’s body. Other methods of attachment include the use of collars, backpacks, ear tags, and inserting the transmitter within the animal’s body cavity through surgery. The method of attachment depends on the size and life history of the study species. Transmitters come in a variety of sizes, so we had to weigh the costs and benefits of transmitter battery life with the impact of additional weight on the individual. Ideally, the transmitter should not have an effect on the individual or the data.
After turning on and attaching the transmitter, it will start giving off a signal similar to a radio station. The antenna picks up the signal and relays it to the receiver. The receiver then interprets the signal through a series of "beeps" with the loudest pointing in the direction of the transmitter. The second loudest beep, referred to as the Back Signal, indicates the opposite direction of the transmitter. It can help to point the antenna in multiple directions to determine where the strongest signal is coming from. Once you narrow down the strongest direction of the signal you can start moving towards the animal. The gain function on the receiver allows you to estimate how close you are to the animal. Increasing the gain amplifies the signal and allows you to hear it from further away. As you move closer to the signal and the animal, you should slowly decrease the gain until it is almost all the way down.
In our study, we needed to weigh individuals every day to see when females laid their eggs. In order to do this, we used radio telemetry to find exactly where the lizard was. Because we are working with a small cryptic species, we do not walk straight towards the signal to ensure that we do not step on the lizard. As we got closer to an individual, we would start circling in on it and trying to visually find the lizard or its burrow. After locating the lizard, we recorded GPS coordinates and collected data on weather and lizard behavior.
Over the course of our study, we affixed transmitters to 69 individuals. Many of these individuals were tracked multiple times, resulting in 80 tracking periods. A majority of these lizards were tacked for multiple weeks 2-3 times per day. This resulted in 2,827 fixes, or locations. The use of radio telemetry provided insight into the behavior and movement patterns of gravid female Flat-tailed Horned Lizards.