Deep in the heart of Panama, nestled amongst the rainforest flora and flanking the Panama Canal, is the little town of Gamboa. And here in this little mysterious town exists a gem of the Smithsonian that is famous for its groundbreaking work in tropical biology. The Smithsonian Tropical Research Institute (or STRI) has been dedicated to studying tropical habitats and wildlife since 1923, hosting over 1,500 scientists per year. I have been lucky enough to become part of this amazing institution, and alongside Professor Alex Trillo and STRI Staff scientist Rachel Page, I have been working with Trachops cirrhosus, the Fringe-Lipped Bat in field experiments to study their preference for prey species based on auditory stimuli. My name is Samantha Siomko, and this is the story of how I became Batgirl.
Trachops cirrhosus, or the fringe-lipped bat, has been the focus of many studies here at STRI because of the unique relationship with its favorite prey: frogs. Trachops hunt by eavesdropping on frog calls, using auditory cues from the frog’s mating calls to locate them. This is useful when studying their behavior, because we can use playbacks of frog calls in the field to lure the bats to what they think is a meal. Trachops are very social bats, living in roosts of dozens of individuals in caves, tunnels, hollowed trees, etc. They hunt using echolocation as well as auditory and visual cues to locate prey. Spanning all across Central and South America, from southern Mexico to Brazil, they prefer lowland tropical forests with plenty of open area to fly.
Dr. Trillo is interested in the sensory mechanisms that enable predators to find their prey. In this specific experiment, we investigate how bats choose which frog to prey upon when these frogs call from a mixed species group. Previous studies on insects and wildebeests show that individuals are preyed upon less when in a group of their own species. However, many frogs call from a mixed species group. Trachops show equal preference for both of the frog calls used in experimentation, the Hourglass Treefrog (Dendropsophus ebraccatus) and the Tungara Frog (Engystomops pustulosus). We are trying to quantify whether bats prefer to attack the more prevalent species, or if is it easier for them to locate and attack a frog when it is the sole member of its species in a group. The hypothesis is that, when in a mixed group such as this, a predator will be able to more easily pinpoint and attack the less common species, because it can be more easily distinguished from others in a group. If you can imagine how much easier it is to keep track of an orange fish in a pool of black fish, or vice versa, you have a good handle on the “oddity effect”.
Each night we set up six speakers, five of which are playing one species’ call (the common species) and one of which is playing a call of the other species (the rare species). We switch the rare species each night. We use infrared cameras to record visits to one of the speakers playing a common and a rare call, and the videos are then analyzed to determine the number of bat predatory visits. Frog models are also used to satisfy the bats’ use of echolocation cues. Shown below is a Trachops cirrhosus bat visiting one of the speakers. Bats are not the only species that use frog mating calls to locate prey. A species of blood-sucking midge is also attracted to frog calls, but they will attack E. pustulosus with more frequency than D. ebraccatus. We also test the midge’s preferences for common versus rare individuals in mixed-group species. Flies attracted to a speaker are captured on fly paper, and the number of individuals who are attracted to that species’ call are determined.
Why is this important? If the less common species is singled out more often in a mixed-species chorus, this would influence the locations from which frog species calls and whether they should actually call on a certain night depending on the species in the chorus. Having to account for this would influence a frog’s reproductive success as well as overall survival, which is especially important in the light of amphibian decline and a recent reduction in population numbers.
When Cultures Collide
My time down here is extra special because of Dr. Trillo’s vision to start a “Bi-national Internship.” This means I get to work with a Panamanian student, allowing for the two of us to exchange information that we would otherwise not be exposed to. Sara Vasquez and I have become fast friends, and she has already taught me so much about species names and Panamanian history and how to properly cut up a pineapple (seriously, there’s a very specific way to do it). It has so far been an amazing opportunity to work alongside her, and I hope she is learning as much from me as I am from her.
More Batty Adventures
We sometimes get the chance to help out other researchers here at STRI, especially when they need to capture wild bats in order to study their behavior in a flight cage. To do this, we help put up mist nets, thin nets covered in pockets to hold tangled bats, over bat flyways. There is always a need for extra hands to help out with this, and I get the opportunity to interact with all types of bat species, which is one of the most exciting parts. I mean, look at their little faces. What’s not to love?
Bats aren’t the only cool thing we see here. On a regular basis, I come across strange and wonderful species, giants frogs, sloths, anteaters and scorpions the size of your hand! Panama has more biodiversity than you could imagine.
Having the opportunity to come here has been incredibly humbling, and I am so glad I was given the chance to experience all of these amazing things and work with all of these amazing people. Holding a bat in your hand can be a life changing experience. Being able to actually look at one of these elusive creatures in the eyes and feel the membrane of their wings is such a great experience. These are intelligent, amazing creatures worthy of more respect than they get. But I know that, as long as places like STRI exist and as long as there are people who care so much about them, there is still hope for these wonderful creatures.
Other photo credits: Michael Caldwell