Backpacking Lizards For Science: Radio-Tracking Puerto Rican Anoles

Brad Lister and Andres Garcia report from Guanica, Puerto Rico:

Most likely, every researcher working in the field with anoles has had the same questions that we’ve wondered about for many years.  How much time do resident species spend in the canopy where they are hidden from our view? What is the home range of males and females? On average, how far do individuals move per day? On days when most of the lizards in a given habitat seem to disappear, where do they go? We tried to answer these and related questions by conducting hundreds of hours of observation on Anolis nebulosus in the Chamela dry forest in Jalisco, Mexico. Anolis nebulosus is very rare in this area and we spent more time finding lizards (2-3 hrs/individual) than actually making observations. Often, after hours of searching, the focal individual would disappear from view within minutes.

Obviously the ability to easily find and track small anoles using radio telemetry would be a major asset in our efforts to understand their behavior and ecology.  Previously, transmitter size limited radio tracking to relatively larger lizards such as Sceloporus, Phrynosoma, and Ameiva. Recently, however, Advanced Telemetry Systems has developed 0.2 and 0.5 gram transmitters that make tracking even 3-4 gram female anoles feasible. We are currently in Puerto Rico continuing with our research on climate change and Anolis ecology, and decided to use the ATS transmitters to track A. gundlachi, A. cooki, and A. cristatellus.

The photo to the left illustrates the ATS equipment we are using in the Luquiilo rainforest and the Guanica tropical dry forest. The brown case contains the ATS R410 scanning receiver. The receiver is very easy to use and program. It allows the creation of a different channel for each lizard that has a transmitted attached to it. Every transmitter has a different frequency so you can identify which lizard you are tracking from the particular frequency the transmitter is tuned to.  The frequency received by any channel can lie within a 4 MHz range. The antenna is a three element folding Yagi which connects to the back of the receiver via a 1.5 m coax cable. For better discrimination of the transmitter’s “pings,” sent out at 5 second intervals, earphones are also plugged into the receiver.

The photo at the top shows an 8 gram, adult male A. cristatellus from Guanica with a 0.5 g transmitter sewed to the dorsal surface of a custom made stretchable, nylon mesh jacket. A 2.5 cm transmitting wire protrudes from the back the transmitter.  After searching the literature for transmitter attachment methods, we decided that none of the available designs were appropriate for small anoles. After many attempts, we converged on the nylon jacket design. In brief, we first sew a 3.2 x 5.5 cm rectangle of the fabric into a tube. We then pull the tube over the lizard’s head and body, and make two small cuts on the ventral surface which we stretch to a larger size in order to insert the front legs. To attach the jacket more securely, we make a series of stitches encircling the anterior edge of the jacket, and then carefully tie the two ends of the thread together so the “cinch” constricts into a snug fit. Another cinching thread is also sewn around the posterior of the jacket. Finally, we sew the transmitter into a tight bag of the same fabric, and then sew the bag onto the dorsal surface of the jacket.

Caveats include the following: (1) The transmitters are pretty expensive, especially the 0.2 g variety; (2) The very small batteries mean that the transmitters last only three weeks or so at fairly slow (1 per 5 sec) transmission rates. The faster the transmission rate, the shorter the life time of the transmitter; (3) The jackets work great, but are very labor intensive, i.e. three  hours or so. Definitely not recommended for projects with lots of anoles! The quickest way to attach transmitters is to just glue them  to the back of the lizards, but we did not have sufficient time to test the reliability of this method.

Our initial test in the Luquillo rainforest with a 9 gram, adult male A. gundlachi worked better than expected. We could pick up the transmitting signal 30-40 meters from the lizard, and within minutes could find the tree where the individual was located.  Over one 24 hour period, our focal male utilized three adjacent trees whose trunks were 3-5 meters apart. Unfortunately, we were not able to see the lizard in any of the trees, which suggests that at least for one day this one male was spending a lot of his time up in the canopy.

So all in all, a successful proof of concept. No more “large lizard envy” for us!  On to Anolis GPS collars, mini-cams, and automated, continuous tracking!