Catching Túngara Frogs in Palo Verde National Park

By Genevieve Valladao

Up until a week ago, I had never touched a frog. I prefer big predators – jaguars, sharks, crocodiles – organisms that humans aren't able to just grab and play with. So, when I found out that one of the first research projects I was going to be working on in Costa Rica involved trapping frogs I was a little nervous. The project was designed to test for effects of Belostomatid (Lethocerus annulipes) predators on site selection of prey Túngara frogs (Engystomops pustulosus). It involved capturing Túngara frogs at ten different sites, marking each of them individually, applying a treatment of Belostomatid chemical cues to half of the sites the next day, and then checking the sites the next night to see how the dispersal patterns of the frogs were impacted. Túngara frogs mate in small pools of water, so the study sites for our experiment were large puddles along the dirt road outside of the Palo Verde Research Station. Our program was split into two groups, each going out to catch frogs a different night and I was assigned to the second group.  

Photograph courtesy of Ray Hopkins

            Group one caught 48 frogs individual frogs the first night of the project, but also came back covered in mud and mosquito bites. Their complaints made me even less excited to go out the next night. But when night rolled around the following day, I put on my rain gear, rubber boots, headlamp, and face mosquito net, and headed out. I was unsure of what to expect. “Okay,” Brian said about 100 meters from the station, as we came up on our first puddle and he handed each of us a small plastic bag. “This is our first site.  Surround the puddle, grab as many frogs as you can, and drop them in your bag.”  Before I could question how I was even supposed to catch a frog, Brian and the rest of the students were along the edges of the puddle, shining their lights in the water.  Two frogs were caught at our first site.  As Brian tagged and documented one of the frogs, I watched the way he held it by the back leg.  “Can I hold it?” I asked - I did not want the first time I had to hold a frog to be one that I was trying to catch for our project.  I was not at all confident that I would be able to hold it without either hurting it or letting it go away.  Brian handed the small frog off to me and I got to get a good look at it - it was a male so its throat was stretched out from calling to females, which was amazing.

Photograph courtesy of Milena Cambronero

            We didn’t catch many frogs the rest of the night, possibly due to the puddles being small from a lack of rainfall.  And I stayed in the back of the group when we would approach a site, so the few frogs that we caught had already been captured by the time I came up on the site.  Sometimes, after a frog had been tagged and released, I would try to recapture it for practice.  Sometimes I would be able to catch it, and other times it would slip through my hands. I was relieved coming up on the last site – I hadn’t been the first to spot any frog so I hadn’t had the pressure of catching one.  But as I ran my headlamp over the puddle, my light illuminated something in the water – a Túngara frog.  I palmed it, just as Brian had instructed, and was able to pass it off to be marked.  I had caught my first frog for our project!

            The day after our experiment was supposed to be finished, it poured rain.  Frogs love rain.  So Brian asked for volunteers to go out one more night and survey all of the sites again.  I had practiced capturing frogs so much the prior night, but only caught one that contributed to our dataset.  So I geared up, this time in a full body bug net, and headed back out.  As soon as we got down to the road we could hear the Túngara frogs calling.  Every site was full of them, we caught 58 frogs for the night and I caught almost a quarter of them.  By the end of the second night, I was completely comfortable handling the frogs and would catch them for fun to try to identify their sex or just to watch them swim away after being released.  I even caught a large toad I saw along the road just to further examine it.  Having to catch frogs during my first week in Costa Rica was a great introduction to my OTS program.  It immediately forced me out of my comfort zone and taught me to not be afraid to try new things. I know that catching frogs is the first of many experiences that will push my comfort zone this semester in Costa Rica, and I can’t wait to see what direction I will be pulled next.