The Great Mexican Bat Bash

NOTE: No bats were harmed in the making of these movies or during data collection!

This summer we spent developing some projects in Mexico. We mistnetted bats and
recorded their calls using ultrasonic detectors. This methodology is great fun when it works, but we did spend a lot of time fussing with equipment, some of which we never did get to work. As a side topic: last summer I had hired an undergraduate (with a dual major in wildlife science and computer science—note to those of you looking for careers!! These skills are highly valued!!) to work in Delaware with one of my graduate students. She had our program figured out in three days and was instrumental (forgive the pun) in getting our equipment working, but sadly, she wasn’t in Mexico with us. We did, eventually, get the ultrasonic detector working and hooked into the laptop to record bat calls. This detector translates bat calls (which are usually at a frequency too high for human hearing; greater than 20 KHz) into lower-pitched sounds we can hear. Then we can download these calls onto a laptop to view them. These techniques allow us the listen in on bat behavior.

We were in the State of Jalisco along the west coastline. This area is known for its beautiful beaches, great reefs, pozole, a soup with hominy, and ceviche, raw fish or seafood marinated in lime juice. The habitat here is classified as dry tropical forest and most of the trees are bald during the dry season. We were lucky to be there at the beginning of the rainy season, when the trees just start to leaf out. Within two weeks the landscape went from brown and grey to bright green. It was a novel experience for someone used to the ever humid and incessantly green of humid tropical forests, such as the Amazon.

In Mexico, we used mistnets (very fine threaded large nets that are used to trap both bats and birds) to capture bats. We then recorded information about the bats (sex, weight, size, reproductive condition) and turned them loose. Although, we were very careful and gentle in handling these guys, a few became very aggravated! See the first video clip. You can hear Luis and Pamela talking about the bat (Artibeus intermedius) and you can also hear the bat yelling at us. Luis has red color on his gloves; this is not blood, but is bat feces loaded with red-colored cactus fruit juice! If we translate what the bat is saying, it’s something like this: “Hey, you big lout! Let me go! I’m going to call my lawyer! What’s going on here, anyway!”

We hear this bat in the video because bats’ distress and defensive calls are pitched at lower frequencies than their commuting or foraging calls. It makes sense. If a bat wants to scare away a predator, its angry calls should be in the audible range.

We also recorded bat calls in the field for several hours per night. We recorded bats at various locations and habitats using ultrasonic detectors. One of the most fun places we went to was right at the beach outside of an open restaurant and bar. In their parking lot was a large calabash tree (Crescentia alata). This species of tree has flowers and fruit that grow directly from the trunk and it is pollinated by bats. As we recorded bat calls, we tried to get some video of bats flying to the flowers, but it was very difficult because they were moving so fast and we were juggling numerous pieces of equipment. We did get this interesting video, though. You can see the flowers on the tree as I pan across it. In the background you hear music from the nearby bar. The loud chirps are the leaf-nosed bats “hitting” a flower for nectar. As they stick their head into a flower while on the wing, they make a very distinctive sound that is different than their approach call. As you watch the video, you will hear a human cough, and then look at the upper left of the frame to see a quick little bat fly by. You also hear a soft hissing sound in the background. That is the ocean, only 100 meters away.

It made for a rather amusing scene: I sat in the back of a small pickup holding a laptop and the camera, while Dave held the bat detector close to the tree. The restaurant’s customers drove up into the parking lot, which was patrolled by a couple of large, possibly armed men who had kindly allowed us to be there. Both of us are wearing headlamps and rumpled field clothes, while the parking lot guards wore uniforms. The customers were in linen suits and tiny cocktail dresses and spike heels. We got a lot of curious looks, but it was fun to hear the music while we worked! At least this night they were not playing heavy metal. Generally, the bat detector did not pick up the sounds from the music because the frequency was too low (the detector is tuned to the higher frequencies that humans can’t normally hear). However, car engines and the occasional pop-top have sounds that range into the ultrasonic and these made for some very interesting patterns on the computer screen!

For why bats are important and also at risk, See Tigga’s blog: http://www.pulseplanet.com/sci-diaries/sd_kingston/

For more on the ecology of the area, see:
http://www.worldwildlife.org/wildworld/profiles/terrestrial/nt/nt0217_full.html

As professors, one of the biggest challenges we face is finding projects for undergraduate students that will convey the thrill of scientific inquiry with the practical side of semester class structure. In many cases there just is not time to conceive of, implement, and complete a project in the 10 or 15 weeks the class will run. Field courses, like the one I co-teach in Belize are even more restricted time-wise. We get a total of 14 days in Belize and much of that is spent visiting sites and listening to lectures. We spend the majority of the time at the rainforest site, BFREE, but with all the activities we do, we only end up with four days to take data on our research projects. What to do? We work on short projects that garner a lot of data quickly, that are doable close to the bunkhouse and dining hall, and are scientifically alluring. It has taken some finessing and trial-and-error to find projects that will work. Fortunately, technology helped out! We discovered that with our bat detectors, we could get estimates of bat activity levels between two habitats at the same time. We also have set up camera traps to develop an idea of what terrestrial mammals are present in the area.While the camera traps are fun, they don’t yield rigorous data; we can only tell what species we “capture,” and that will not be an exhaustive survey. Nor can we tell anything about population size only using four cameras. We have also attempted to set up “traps” with peanuts circled by non-toxic florescent powder. This setup would hopefully allow us to estimate the rate of seed predation, and coupled with camera traps, determine what species are eating seeds. However, most of our set-ups never lost any peanuts and the one where the peanuts disappeared every night did not get any pictures. We aren’t sure if whoever was taking the peanuts was too small to set off the trigger on the camera trap (like a little spiny rat) or the equipment failed for another reason. Well, there’s downside of technology! However, we did get one extraordinary photo of a jaguar walking past one of our camera traps. This photo tells us a few things: it’s a male, and it is not the same jaguar that we “captured” last year (compare the spots on the photos), it was within ¼ mile of the bunkhouse, so students should be cautious during bathroom trips, and it looks healthy. With more cameras, we could potentially get an idea of how many others are out there, but that is for another time.

On the other hand our bat project worked really well. After the first night of collecting data at dusk by standing with bat detectors in one hand and swatting at the continual blitzkrieg of mosquitoes with the other, one of the students had a brainstorm that we could set up a couple of open-screened tents and sit inside. This plan actually worked well and our suffering was greatly diminished! And without a loss of data, that is, the screening did not seem to interfere with what we could pick up with our ultrasonic bat detectors. We had one tent set up in the middle of a clear-cut area (actually the helipad mowed and maintained for emergencies) and one tent set up along the edge of the forest. The hypothesis we tested was whether there is a difference in bat activity between the two habitats. One would expect that bats would forage in areas where they can maximize their energy intake while at the same time staying safe. We thought that bats would forage more along the forest edge because that would give them some cover from night flying predators (owls maybe), and this is the pattern we find in our home state of Delaware. But in Belize, at least in our little microcosm of the rainforest at BFREE, we found more bats foraging in the wide-open area. We were able to see this result in just the four nights of data collection and not only did we get usable data from this mini-project, and set the stage for future student research projects, but it was an excellent introduction for students in how to conceive and implement a scientific inquiry.

One of the projects we tried last year that DIDN’T work well was, unfortunately, our dung beetle projects. We had hoped to examine species diversity in different habitats and also to look at dung burial patterns. Well, one of the reasons it did not work was lack of good bait. We used horse dung and any good dung beetle biologist working in the Neotropics will tell you that horse dung is not particularly attractive to dung beetles. Hmmm, so what is attractive? Again, as any good dung beetle biologist will tell you, primate dung is very attractive; actually the human variety has been shown to be the MOST attractive (brings in the most species to traps). Folks just plain got squeamish about contributing to this scientific effort. Somehow, research on bats is more appealing to undergraduate college students! So, we go with where the interest is highest and we can actually get data fast.

I teach a course with a colleague every winter break called “Tropical Agriculture, Ecosystems, and Conservation”. This course takes students to the wonderful country of Belize in Central America. We are based at the BFREE site (for Belize Foundation for Research and Environmental Education) near the Bladen Nature Reserve in Southern Belize. In addition to lectures, field outings, and hands-on demonstrations, the students all participate in research projects. I discuss one of those projects–our traps for dung beetles–in the science diaries.

Another student project involved using camera traps to determine what kind of animal activity was in certain locations around the reserve. These cameras use motion and heat detectors to trigger the shutter. You set them up in a likely spot, set the trigger, wait for a day or so, and Voila! photos of animals you would not normally be able to see. Except, it was not quite that easy. Our biggest problem with these digital cameras was figuring out the instructions, which had to have been written by folks from Mars. That took four people about four solid hours of aggravation. Also, because there was no way to download the pictures (the camera trap had no screen), we had to wait until we were back in the states to see what was in the pictures. We had several hundred shots of nothing but “blanks” – that is, camera shots with no animal pictured, often triggered by insects or rain. Then, to our surprise, there was the shot of our male jaguar! A cat clearly on a mission! Camera traps, so called because you “catch” an image of the animal, are used for mammal surveys, especially with animals that can be individually identified from markings, like our jaguar. Once set up, they can be used to count the number of “recaptures” (those animals that appear more than once in photos), and the population size can be estimated from a ratio of the number of “recaptures” to “total captures”.

The other animal that we “captured” on camera was a low flying bat! The camera was only about three feet off the ground, and most cameras take several seconds to trigger the shutter once the infrared beam is broken. Our camera, on the other hand, triggers almost immediately, so even a fast flying object can be captured. It was still a very lucky shot!

For more about jaguars, visit: http://savethejaguar.com/jag-index

For more about bats: http://www.batcon.org/home/default.asp

Many people wonder what biologists do, especially those biologists not working in the medical fields. As an ecologist, I try to explain by saying that I work on the interconnectedness of living things. But how actually do I do that? As biologists, we are encouraged to examine the world through questions, as in “what is the question you are trying to answer?” That question could be how a theoretical construct fits the empirical data or something as simple as: “What is the use of a dung beetle, anyway?” Despite this urging from fellow scientists to frame our research around a specific question, most of use get into a line of questioning because we just plain LIKE the animals (or plants!). One of my problems is that I like so many different animals. I see an animal and I think, “Gee, it would be cool to work on frogs!” However, there is only so much time, so I have narrowed down my animals of choice to those that disperse seeds, mostly monkeys and dung beetles. Monkeys obviously disperse seeds through endozoochory, a fancy name for swallowing a seed whole and passing it out later with poo. But how do dung beetles disperse seeds? By finding the monkey dung and burying it, thus taking seeds along with it! The dung beetles aren’t interested in seeds, but they need to bury the poo fast to keep it for themselves, and they usually don’t take the time to remove the seeds. Thus, seeds get “planted” underground, safe from seed-chomping rodents and nasty fungi. So, I study the way that monkeys and dung beetles interact and help to move seeds around and regenerate the tropical rainforest. And I ask these questions: How do monkeys and dung beetles in a particular area contribute to forest regeneration? What is the impact of certain monkey species on seeds? What can we do to preserve this important interaction and the animals involved?

But, I have other responsibilities than just working on my monkeys and dung beetles. As a university professor, I teach, I contribute to the university community through service, and most importantly, I also have students that work on research projects and only some of those students can work on monkeys or dung beetles. Some of the other projects I work on with my students include: feral horses as seed dispersers on barrier islands (think Misty of Chincoteague!) and bat activity patterns on farm-woodland interfaces.

Over the summer, I will be posting notes to this blog about many of these projects.