Pulling it All Together: Biology, Spanish, & Education

Our time in Costa Rica is wrapping up, but not before a culminating event to showcase what we’ve accomplished.  After completing our independent research projects, we held a poster symposium for a visiting group of students from the Universidad Estatal a Distancia.  As the students had interests in ecology but were pursuing degrees in a wide variety of disciplines, we got the chance to practice communicating science to a broad audience.  Putting our Spanish skills to the test, we presented our findings to the students and then led them into the forest to explain our field sites and data collection.



Title translation: Effects of interference noise on Dendrobates pumilio calling behavior.

Overall, the perfect end to our journey in biology and Spanish in Costa Rica!


To Catch a Frog

Walking through La Selva’s forested trails, many sounds greet you: peccaries chomping on leaves or tree roots, crested guans trilling from the canopy, lizards scuttling at sonic speeds over leaf litter, and cicadas chirping so loudly and monotonously that they almost fade into the wind.  Cutting through these noises you can hear the call of the strawberry poison dart frog, a squeaky, repetitive ch-ch-ch-ch sound that can last anywhere from 10-40 seconds.  Males call from their territories (about 2-3m diameter of forest floor) to advertise themselves to females, who have the luxury of choosing the guy with the most attractive salutation – usually, they go for males with fast, long, and loud calls.  With all of the noises that surround them in the forest, how do male frogs decide when it is worthwhile to call, and when they might get drowned out?  We set out to investigate this question empirically, and as our interference noise of choice we selected one of the most common natural noises that is likely to mask a frog’s call (since it occupies the same sound frequencies)—a cicada call.

Before we could perform any experiments, we had to catch our test subjects.  Strawberry poison dart frogs are active throughout the day, but calling activity is highest from about 7-9:30 a.m.  Their bright red aposematic (warning) coloration makes them easily visible against the drab shades of brown that compose the leaf litter, but unless you’re up close their small size (less than an inch long) often makes them undetectable by the human eye.  Instead of going by sight, we relied on sound to guide us to the frogs.  After just two days of practice in the field, we had our method down:

Step 1) Walk slowly down the forest trail with your ears peeled.

Step 2) When you hear a call (ch-ch-ch-ch….) gauge how close you think you are to the frog (walking with quiet feet in the direction of the sound with help with this).  If it’s more than about five meters off the trail, forget about it—the frog will stop calling well before it comes into view.  But if it’s nearer than that, proceed to step 3.

Step 3) Contrary to intuition, do not try to sneak up on the frog.  Most will cease to call when they hear footsteps approaching even from a decent distance, so taking brisk strides in the direction of the call will get you closer to the frog before it stops calling.

Step 4) Get as close as you can before the call stops.   Scan the area, taking care to check perching hotspots, such as tree roots, logs, and tops of leaves (exposed places where a female would be likely to see him).  Nine times out of ten, a little strawberry-red dot will catch your eye.

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Male strawberry poison dart frog (right) calling to a female (left)


Step 5) Lunge.  These frogs move in quick, jerky hops that make them hard to follow or corner.  So roll up your sleeves, keep your eye on the prize, and grab!

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Strawberry poison dart frog hopping through leaf litter


These tactics worked pretty well for catching male frogs, but we also needed some females to provoke the males to call in the lab.  Since females don’t provide calls to follow in the forest, we had to rely on sight and a bit of luck to find females hopping along the forest floor.  Males and females are easily distinguished by examining the gular (throat) region, which is dark grayish-blue on males and red or asymmetrically patterned on females.

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Male — note the dark grey gular region on its otherwise red vent

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Female — this one has some light blue patterning but distinct lack of a gray gular


Back in the lab, we set up a cardboard box arena to conduct our experiments.  We placed one male and one female on opposite ends of the arena and waited for the male to call, which usually happened after only a minute or two.  When the call began, we started audio recording on our fancy recording device, i.e. the voice memo app of an iPhone 5.  Depending on whether the trial was a “noise” or a “silence/control” treatment (predetermined) we would wait 10 seconds into the frog’s call and then either play the cicada call playback (obtained from Macaulay Library, Cornell Lab of Ornithology) from a speaker for 10 seconds or do nothing during that time.  We continued to record the frog calls for 10 seconds after cicada playback to get an idea of how quickly they can rebound from being interrupted by interference noise.

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Experimental arena, and adjacent box for placing iPhone microphone/audio recorder

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Frogs in the arena (left: female, right: male)


After testing over 60 frogs, we ended up with a pretty nifty result.  Frogs lowered their call rates (speed of the ch-ch’s) during cicada noise compared to pre-playback, indicating a decrease in calling investment when faced with interference noise.  Interestingly, males neither increased nor decreased their call volume from pre- playback to during the cicada noise, suggesting that males always call at their maximum volume and maintain it even during masking noise.  This could mean that energy expenditure is mediated more by how fast the calls come rather than how loud they are; in other words, calling loudly is not as big an investment as calling rapidly.

What does this mean for frogs?  Cicadas and other sources of noise are ubiquitous in the forest, and a frog that calls to attract females only in periods of silence will likely suffer reduced reproductive success.  Studying how natural acoustic interference affects animal communication can help us predict the effects of added anthropogenic noise as forested areas become more developed.

Inside the Tropical Wet Forest

La Selva Biological Station is the epitome of a tropical rainforest (although by Holdridge life zone classification it is actually a tropical wet forest, experiencing a wet and a wetter season as opposed to a full year of downpours) and is OTS’s most popular field station for researchers.  Located at the junction of two rivers in the province of Herendia, La Selva (literally “The Jungle”) is home to the widest diversity of wildlife we’ve experienced in all of our time in Costa Rica.  Walking down any of the various trails that surround the station, crossing the famous hanging bridge, or even just sitting on a bench in one of the open areas on campus, you’re bound to see some amazing creatures.

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DSCN6453 Hanging bridge (above) and, on the other side, Sendero Tres Rios (Three Rivers Trail; below) at La Selva Biological Station.


Our first class at La Selva consisted of no textbooks or powerpoint presentations, but simply a nature tour through the trails in order to begin to learn the landscape.  Peccaries were the first to greet us at the trail’s entrance.  While strange and exciting at first, these “pets” of the station would come to elicit no more than a sideways glance within just a few days.

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peccaries 2 Collared peccaries, eating and lounging around campus

Less than three steps onto the trail we spot one of the iconic creatures of the tropical rain forest habitat: the strawberry poison dart frog.  About the size of a thumbprint, these aposematically colored frogs advertise their toxicity to predators, making them easy to spot amid the collage of greens and brown that composes the forest floor.

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Strawberry poison dart frog (also called the blue-jean frog–can you see why?)

During our hike, we encountered some old favorites from our days at Las Cruces, including the crested guan, chestnut-mandibled toucan, and Cherri’s tanager.  New to the list was the collared aracari, considerably smaller than the other toucans we’ve seen and sporting rich flame-colored feathers and bill.  These guys have become a fairly regular sighting in the open areas on campus or in trees towering over the hanging bridge, but every time they’re as surprisingly stunning as the first.

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Collared aracari

Rounding out our tour was one of La Selva’s notably precious rarities—the eyelash pit viper.  This venomous snake that could fit in the palm of your hand when neatly coiled gets its name from the two small scales that protrude vertically above each eye.

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Eyelash pit viper (Photo credit: Rachel Moon)

The structure of the station is expertly done, creating spaces that are conducive to seeing animals up close without being in their way.  Sitting at breakfast in the open-air dining room, you can watch as kiskadee parents gather dragonflies, berries, and whatever else they can find to feed their chicks in the nest tucked against the side of the building.  Both parents make trips to the nest, never letting more than five minutes or so pass without providing another snack for their offspring.  The constant peeping from the little ones reminds the parents that no matter how much they get fed, they still have room for more.

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Great kisdadee with a dragonfly meal

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Great kiskadee chicks begging for food in the nest

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Parent returns to nest to feed chicks

While crossing the hanging bridge to get to class, this rufous-tailed jacamar zipped just over our heads and landed on the top of a tree, which is nearly at eye-level when standing on the bridge.  After a moment’s rest it flew up again so quickly that it nearly vanished from sight, and in one swift movement returned with a butterfly flattened within its beak.  We watched as it literally tore the insect to shreds through a combination of thrashing its head and making quick snapping motions with its beak.

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A hungry jacamar

On an early-morning hike to beat the heat, we crossed paths with another poison-dart frog, this one of the green and black variety.  As it hops about in and under the leaf litter, I’m reminded of its plastic toy replica I played with as a kid.  A bit further along, this glasswing butterfly flutters out of the forest edge, disappearing and reappearing before our eyes.  When it finally lands on a leaf, we see that its wings are completely transparent.  It seems like tropical creatures have much more creative ways of evading predation than prey in the temperate zone, whether they are flaunting their unpalatability or making their predators dizzy with confusion.


Black and green frog


Glasswing butterfly


Crossing the bridge once more in the late afternoon to get home to our comfy cabins, I see something large and hairy crawling along the bridge cable.  A sloth?  But wait, it’s moving, and not in slow-motion.  Getting closer, its form becomes clear: a howler monkey!  And she’s with her baby, too.  The pair sits less than five feet above my head, tails wrapped around the cable for support and relaxed gestalt suggesting that they barely notice me at all.

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Howler monkeys on the bridge


Walking around La Selva, ecological questions come naturally.  Why do leaf-cutter ants travel so far from their nests and to the top of the canopy to gather leaves?  What drives variation in the amount of blue and red coloration in strawberry poison dart frogs?  What do all of the different oropendola calls mean to the other birds?  How did so many types of drip-tips on plant leaves evolve?  And why is it that the tropics have so much biodiversity?

Regrettably, intriguing questions such as these are difficult to tackle in four days, which is the allotted time we have to conduct an independent research project here at La Selva.  Building on experience from our jacana study back in Palo Verde, I’ve discovered that the key to a successful project is to choose a study organism that is 1) interesting, 2) abundant, and 3) at least somewhat cooperative.  For me, it was a no-brainer: the strawberry poison dart frog.  Since the males of this species spend all day calling, usually from a conspicuous perch, there were plenty of interesting directions from which to examine their acoustic behavior.  The question, how we did it, and what we found coming soon!

Rainforest of the Sea

Entering the mangrove forest is like dipping into a strange dream where you’re not quite sure which way is up and your surroundings seem other-worldly.  Seated on the boat and looking up, the leafy branches of mangrove trees have come together to form a whimsical archway that blocks the outside climate—whether rain or sun—from penetrating.  Tall, gangly prop roots stretch out like stilts from the bases of the small trees and dangle underwater; emerging from the water and scuttling up the roots are crabs, a parallel to the scampering insects and lizards of terrestrial forests.  Mollusks foul some of the roots, indicating the height reached by the water at high tide.  The place is undoubtedly aquatic, but looking straight up you could fool yourself into believing there is solid ground and soil supporting the foliose trees.

The short boat ride through this surreal habitat at the interface of land and sea was just what we needed after a long, complicated journey over the border from Costa Rica to Panama, involving crossing on foot over a very dicey wooden bridge with tremendous gaps between planks that revealed the crocodile-filled river below.  But our habitat of study at the field station on the island of Bocas del Toro was not the mangrove forest; rather, it was the adjoining coral reef.

The first striking thing about the coral reef is that it comes out of nowhere.  Bobbing up and down on the waves in the mid-morning drizzle, we couldn’t see to any depth in the turbid water.  You wouldn’t think there was anything besides sand beneath the surface, but as soon as we stuck our heads underwater, a vibrant community of fishes, corals, and other marine invertebrates greeted us.  Through my snorkel I squealed with delight, taking a hundred mental pictures a second and whipping around in all directions, not sure what to investigate first.

With no trails to follow, as we so comfortably have in terrestrial forests, I decided to pick a fish (a yellow butterflyfish with black stripes stood out) and follow it.  We swam over large yellow brain corals, past bright red tunicates puffing sandy squirts of water, between bunches of threatening-looking sea urchins wriggling their sharp spines.  It was interesting to see how everything in the habitat seemed to use each other: brittle stars wrapped themselves around coral, and fish munched algae off of the reef or dashed into anemones to hide.  The coral growing on the roots of the mangroves provided a seamless transition between the two habitats.

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A glimpse of the underwater view at Bocas del Toro.(Photo credit: www.123rf.com)

Suddenly, a shimmering something caught my eye.  It was a fish, slate blue (nearly fading into the color of the water) with pinkish fins and generally nondescript except for the fact that about every other scale on its body was shimmering with iridescence.  The fish looked inexplicably familiar; after a moment I matched it to the illustration from an old childhood book, “The Rainbow Fish”—a heartwarming tale in which a glamorous but egocentric fish learns the virtue of generosity by giving away her flashy scales to friends without.  The fish I had spotted resembled this character so strongly that in my excitement I dove to get a better look, inhaling saltwater through my snorkel in the process.


Stoplight parrotfish (Photo credit: divers.neaq.org). 


Book cover of “The Rainbow Fish” by Marcus Pfister.  OK, maybe they’re not identical, but there’s a resemblance.

It turns out that the species’ actual name is the stoplight parrotfish (initial phase).  The “stoplight” aspect became apparent after witnessing the species’ magnificent ability to change color in order to hide.  Farther down the reef I had to do a double-take in order to distinguish one mottled brownish-tan fish taking the color and texture of the coral it was hiding under.  I watched as, in an instant, it darted away while simultaneously morphing into a lighter hue with the scaly texture you would normally expect for a fish.  This lighter morph was the very same “rainbow fish” I’d spotted earlier.

We explored the reef for hours, gliding over the bustling community below while trying to avoid being pricked by a sea urchin or smashing our fins into the fragile corals.  Underwater, we become detached observers, a stark contrast to the sense of oneness you get from walking through a forest.  But, as in tropical forests, diversity abounds in the coral reef as organisms are highly specialized for their distinct niches in these astounding “rainforests of the sea.”

Spring Break at Jacó Beach

When tackling Costa Rica’s jungles or navigating its bustling cities start to wear you down, you find that all you really need to become perfectly content are a few days at the beach.  Although we had merely planned to indulge in Jacó beach’s warm Pacific Ocean waters and slow, gentle waves, our encounters with intriguing intertidal life from the sky to the sand proved that in Costa Rica, natural wonders present themselves even when you’re not on the lookout.

Walking along the fine, gray sand, you’re stepping over a myriad of life.  As the foamy ripples of a crashing wave subside back into the ocean, the sand is puckered with tiny snails hurriedly burrowing into the moist layers of the substrate.  When the remnants of the next wave lick the shore, the snails resurface, use their fleshy muscles to propel themselves forward in a way that is reminiscent of a sea lion using its flippers on land, and then—after this running start—slip into a smooth, gliding crawl.  Viewed from above, they look like tugboats traveling between city ports on a map of the world’s oceans.

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Shifting our gaze from the sand into the lapping waves, we notice zig-zagging darts of movement that could only be fish swimming in dangerously shallow waters.  From the distance, pelicans soar inland, looking for a meal.  While they’re still at least a hundred meters in the air from the water’s surface, however, something else plunges from out of the sky, swoops low on the water, and snatches the hefty fish with ease.  This bird had wings too narrow and a bill too short to be a pelican, but we couldn’t quite make out what it was until it gained altitude directly over our heads.  All at once we saw the kinked wings, forked tail, and white chest against an all-black body—unmistakably, it was the magnificent frigatebird.

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Over the next couple of days we would see these large waterbirds soaring overhead, but interestingly all of them appeared to be females (males have a distinctive red throat pouch).

Another avian friend that likes to scan the beach every few minutes is the scarlet macaw, flying in pairs or small groups from one treetop to another.  Once you know the particular squaaak! to listen for, you can’t miss them.  Often we would watch them overhead until they faded into the mountains, but one morning we were lucky enough to follow their flight to a tree right on the beach.  Apparently ravenous, the pair spent at least twenty minutes feasting on seeds while we gazed, enamored, from below.

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As always when spending time at the beach, our trip came to a close too soon—but getting a taste of the ocean piqued my hunger for more explorations with sea life at the coral reefs of Bocas del Toro, our next field site!

La Semana Santa in San Jose

For Costa Rica, and almost every other country in Latin America, la Semana Santa (Holy Week) is the most important week of the year.  It begins on Palm Sunday and culminates one week later with the holiest day of the year in Catholicism: Easter Sunday.  Each country has a slightly different way of celebrating, but certain traditions are widespread, including the procession through the city streets on Good Friday.

At 9:30am we were on our way to the Metropolitan Cathedral of San Jose when we encountered a street staged with people in costume.  About twelve men staggered in lines of two or three were dressed in ancient Roman centurion garments, gold-colored armor, and helmets fringed with palm-like fronds.  We joined the crowd on the sidewalk, pacing the block to find a good viewing spot.  Behind the centurions was a line of priests, and further back we could see the life-size figure of Jesus carrying an ornate cross set on a platform heavily adorned with crimson flowers.

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People representing Roman centurions line the street.

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Drummers keep the beat that signals everyone in the procession to advance.


Everyone in the procession remained still and waiting; people on the sidewalk were chatting quietly and watching the street expectantly.  Suddenly, the marching band at the tail end of the group began to play—a slow, solemn melody—as four assistants hoisted the platform onto their shoulders, stepping in synchrony so that the Jesus figure swayed from side to side, giving the illusion of walking.  On this cue, the rest of the procession began to walk forward in a rhythmic sequence of steps, with a drum major keeping the beat.  The first step was up and to the left, then up to the right, then straight, and a rest on the fourth beat before repeating the sequence.

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Platform with Jesus figure is carried through the street.


We followed the procession down the sidewalk—past the Soda (general name for restaurant with typical Costa Rican food such as rice, beans, and plantains), the MacDonald’s, the bank—shuffling amidst the crowd of people, a mix of old, young, tourists and ticos.  The procession turned a corner and arrived at a small scene set up on top of a little stage: a woman dressed in elegant robes, clutching a cloth to her chest and facing the oncoming assembly with a mournful expression.  It was one of the Stations of the Cross (Veronica wipes the face of Jesus).  When the men carrying the platform reached the stage, one of the priests began to narrate and we watched the scene while his voice echoed through the streets over loudspeakers.

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Veronica joins the procession, bearing a cloth depicting the face of Jesus three times.


The parade of personages continued in this way, with the cast of each Station joining in the procession as it went.  A little before 12:00 we rounded the corner to the Cathedral.  The final station was performed just outside its gates, and once concluded the platform supporting the Jesus figure was carried inside as the band played for the last time.

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Metropolitan Cathedral of San Jose

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Procession culminates at the Cathedral.


By this point, the small crowd of people we first encountered on the sidewalk had grown into a mass congregation that filled the central plaza and surrounding streets.  The main event had ended, and although the mood was still solemn, the gathering resembled a large community get-together as people engaged in friendly conversation and reunited with neighbors.  Groups took up benches in the park, found their way into the Cathedral, or strolled pensively down the sidewalks on this reflective holiday.

When the rain falls down, the frogs come out

The extreme change in habitat and climate that one experiences after traveling for just a few hours in Costa Rica never ceases to amaze me.  Whereas the dry forest of Palo Verde was bone-dry and scorching hot, Monteverde’s cloud forest is chilly and perpetually raining, thanks to a combination of altitude, topography, and the rain shadow effect.  Clouds moving up one side of the mountain cool and condense at the top and drop lots of rain, making that side of the mountain very wet.  Then the clouds, cool and void of moisture, sink down the other side of the mountain, warming as they descend and making that side very dry (thus, the mountain has cast a “shadow” of dryness).  Our biological station in the Bosque Eterno de los Niños sits near the top of the “dry” side—the Pacific Slope—but the intense winds push rain from the “wet” side up and over the top of the mountain, giving our cloud forest 5000mm precipitation annually (for reference, that’s about four to five times the amount in Boston, New York, or Washington, D.C.).

Monteverde is home to plenty of birds and mammals, but in all the wetness they tend to be less active and difficult to spot.  Instead, a different taxon is more comfortable in this moist environment: amphibians.  Since many amphibians are nocturnal predators, the best way to see them is by going on a night hike!  Huddled in raincoats, our class ventured out into the woods with our flashlights guiding the way.

Looking for frogs in the cloud forest is not an easy task.  Many frogs exhibit incredible mimicry of leaves, bark, and various substrates.  The easiest way to find them is by looking for movement when and where you step.  If you’re up for more of a challenge, look closely on and under each leaf you pass, and sooner or later one of those brownish blobs that you thought was a clump of wet moss or dirt will turn out to be a frog, sitting perfectly immobile as it waits for unsuspecting prey to crawl or fly by.

We encountered several species of ground toads on our walk; the males are rather flat and round and look like a wet conglomerate of sandy pebbles until you get a closer look.  The females are several times larger and much easier to spot from a distance.

ground toad (Rachel Moon)

Male ground toad (Photo credit: Rachel Moon)


By far our most impressive find was the rufous-eyed stream frog, which sports typical “tropical frog” characteristics like bright coloration, slick skin, and large toe pads for gripping to trees.

rufous eyed stream frog (Rachel Moon(

Rufous-eyed stream frog (Photo credit: Rachel Moon)


Not only are night hikes great for spotting frogs and toads, but you are able to see things that you would never consider looking for during the day.  On the walk back to the station, our professor stopped and instructed everyone to turn off their flashlights and look around.  For a few minutes we struggled to see into the dark forest, no one daring to move an inch for fear of toppling into the stream below the trail.  Suddenly someone spotted specks of light on the ground.  It looked as if as if a bunch of lightening bugs had been crushed over top of a leaf—in fact, we were looking at a bioluminescent fungus.  The fungus-covered leaf passed from one person to the next, a mass of sparkling, yellow-green jewels suspended in blackness.

When we emerged from the forest back at the station, we were greeted with another fantastic bioluminescent display as dozens of click beetles circled the trees.  We watched for a while, letting them come up close to our faces and then dart away quickly, until the chilly rain began to make us numb and we retreated into our warm beds with the image of the beetles still dancing in our minds.

Marsh madness!

At the heat of the day, the sun beats down on the ever-drying marsh, now just a series of vaguely connected shallow ponds surrounded by deeply cracked, dusty soil.  Some of the waterfowl have already fled to wetter regions, but other species remain, among them the northern jacana (Jacana spinosa).  This abnormally long-footed inhabitant of marshy areas is a resident of Palo Verde and seems perfectly relaxed in its little remnant of marsh.  But this apparent tranquility is a façade.  Wait around for about ten minutes and you’re likely to watch as, out of the blue, a jacana launches into the air while vocalizing shrilly, lands next to another individual with its characteristic wings-up display, chases its subordinate and assumes its place all within a few seconds’ time.

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Jacanas pecking away at the Palo Verde Marsh


Northern Jacana (Jacana spinosa) displaying, showing wing spur

Jacana displaying, showing wing spur. Photo credit: www.warrenphotographic.co.uk


This kind of intraspecific aggression is common, quick, and mostly results in no physical harm, so what’s the motive behind it?  The dry season is a tough time for these insect and aquatic invertebrate eaters—their food supply is shrinking and their population is becoming denser as everyone crowds around the water holes.  Could these two factors—food availability and density—play a role in triggering aggression?  This is the question that I along with two fellow classmates pursued for our four-day independent research project at Palo Verde National Park.

First, let’s get up to speed on a little jacana biology.  During the wet (breeding) season, it’s clear to see why jacanas might act aggressively toward each other.  Exhibiting a polyandrous mating system, the females hold large megaterritories and two to four males hold smaller territories within that of their breeding female.  Females defend their territory against other females, and males exclude other males.  Once chicks hatch, both males and females (but much moreso males) defend their offspring against predators.  In short, territoriality and chick defense describe aggression during the wet season, but it’s still unclear as to why jacanas exhibit aggressive behavior during the dry season.

For our project, we observed 74 jacanas over four days, going out to the marsh for three hours each morning and afternoon.  In the field, we would select a jacana arbitrarily to be our focal bird for that trial, and each trial lasted 10 minutes.   Next, we assigned roles: one person to be the data recorder, one peck rate monitor, and one distance measurer.  To measure perceived habitat quality, the peck rate monitor glued their eyes to binoculars and counted the number of times the focal bird pecked at the water/substrate over 30 seconds.  This measurement was taken once every minute for the duration of the 10-minute trial, and it gave us an idea of how much that bird valued the habitat—lots of pecks implied there was a high chance of getting food, and few pecks meant that there wasn’t much there to peck at.  To measure density, the distance measurer counted the number of other jacanas within a 3-meter radius of our focal bird, and also estimated the distance from the focal bird to the nearest jacana.  After 10 minutes, we moved on to another focal bird and rotated jobs.

Note that the distance measurer had to estimate distances visually, as it would be highly disruptive to tromp out there and drag a tape measurer from bird to bird.  This meant that the three of us had to undergo “distance training.”  In the grassy airstrip adjacent to the marsh, one person would set up two flags and measure the distance between them using a tape measurer without the other two looking.  Then, standing at a range of 5-20m back (to emulate different scenarios in the field), the other two people would guess the distance to the nearest 0.1m.  By no surprise, we were all rather horrendous at first (especially when the flags were set up vertically, with one in a plane directly behind the other), but after many repeated trials, all of us were able to estimate the distance correctly on average to within 20cm!

After four days of observing jacanas, we got some interesting results.  Perceived habitat quality did not seem to influence likelihood of aggression, but density was more informative.  The average density immediately preceding an aggressive encounter was higher than the average density overall (for all birds at all times during their 10-minute trials).  This suggests that crowding might be a trigger for aggression.  However, if the end goal of aggression were to increase an individual jacana’s “personal space,” we would expect its subordinate to be farther away after the aggressive encounter.  Instead, we found that the distance between two birds engaging in aggression decreased just as often as it increased.  Therefore, jacanas might not be concerned with crowding per se, but rather they defend a particular foraging site (whether or not it presently has food).  In other words, perhaps it doesn’t matter how close your neighbor is to you, so long as he is outside the bounds of where you want to look for food.

Throughout the course of the study, we got the chance to become acquainted with the neighborhood at the marsh.  Spoonbills and jabirus frequented the deeper edges of the water while the ducks tended to hang around the shallower areas, along with our jacanas.

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The neighborhood (background: roseate spoonbills, mid- & foreground: black-bellied whistling ducks and northern jacanas)


Two jabirus (Jabiru mycteria), standing about 4ft tall.


One of our favorite characters at the marsh was the not-so-friendly neighborhood caiman.  Every once in a while, we’d see something log-like moving through the marsh just a little too quickly and with a few too uniform ridges to be a log.  Then it would stop, raise its head straight out of the water, and make several chomps at the air before slowly submerging itself back underwater.  We all jeered at this attempt at ferocity, given that the caiman’s mouth looked barely large enough to fit a small sparrow, let alone any of these waterbirds.  However, we did once find it feeding rather clumsily on what appeared to be a duck carcass (whether the caiman actually killed the duck or found it dead already is unclear).

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Caiman snapping above the water

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Caiman trying to disguise itself under the mud — do you think the jacana in the foreground sees it?


And the white-faced capuchins made lovely company, whether they were playing, jumping through the trees, or, quite often, taking a late-morning snooze.

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monkey sleepmonkey line Capuchins playing in a tree, napping in the sun, and lounging on a branch


We’ll be sad to leave this lively marsh, and all of Palo Verde, but new adventures at the Monteverde cloud forest await us.  (We will be without internet during our stay at Monteverde, but be sure to look for updates later this month!)

Antlions: invisible predators of the soil

One thing that any nature enthusiast can attest to is that in nature, the closer you look, the more you see.  You can find life in the most seemingly inhospitable places, colors and patterns in the blandest-looking creatures, and—in the dry forest of Palo Verde—movement just below the soil surface by invisible insect architects known as antlions.

Antlions are not actually ants (and they’re certainly not lions); rather, they are insects in the order Neuroptera, related to lacewings and dobsonflies.  This morning, we set out to study the antlion larvae which burrow underground and turn ordinary soil into a sudden death trap.  While you very rarely get a look at the antlion itself, you can clearly see evidence of where it’s hiding.

antlion larvae

Antlion (larvae);  photo source: http://www.ipm.iastate.edu/ipm/hortnews/2008/7-30/antlion.html


Look for small (~1.5 in. diameter) funnel-shaped holes in the ground, then stick your nose right up close, wait a beat or two, and see tiny bits of dirt or rock launch themselves out from the base of the funnel.  These silent predators sense vibrations of termites, ants, and other prey near their hole, and then knock them down into the funnel by bombing them with clumps of soil.  Once the prey is deep enough down the hole, the antlion uses its mouthparts to quickly grab its meal and pull it under the soil.  Viewed from above, it looks like the victim is being dragged against its every effort into the underworld.

antlion pit

Antlion pit, ~24cm diameter and 15cm depth


Our assignment was to test how the antlions respond to disturbance—in this case, using your finger to sweep soil over the hole to cover it.  The action could mimic natural disturbance, such as a tapir trampling over the trap, or anthropogenic machinery plowing over the land.  With our study, we were looking to find out how the size (diameter and depth) of the newly made hole changes after repeated instances of disturbance, how soon after the disturbance the antlion recovers, and whether popping the antlion a termite snack ahead of time had any effect on its ability to recover.  In practice, what this experiment entailed was sweeping your finger over the ground and then staring at the same spot of dirt for 30 minutes, 45, or sometimes two full hours before the antlion started to reconstruct its lair.  As I’m sitting there under the shade of a tree, waiting, I’m reminded of a saying my mother used to tell me about a watched pot…

One upside to the often long recovery times is that when the antlion finally does start digging again, it comes as an exciting surprise.  There, in the midst of completely still soil, a grain of sediment suddenly wiggles.  Then the 3-square millimeters around it start to pulse, as if something is about to burst from the ground.  Instead, that tiny bit of ground starts to sink, and you see the tracks made by the antlion’s tunneling.  The antlion digs in spirals to form its funnel, flinging dirt in a firework-like display.

The results from our short study were interesting: antlions tended to build smaller traps than their original after the first disturbance, but repeated disturbances had no further effect on their rebuilt trap sizes.  Furthermore, feeding termites to the antlions had no effect on their ability to recover.  In terms of ecology, this implies a trade-off between energy expended and potential food gain—larger traps take more time and energy, but the larger size increases your range for catching ants.  It also seems like a single termite meal isn’t enough to override the stress of a disturbance and convince the antlion that this location is worth investing in a large trap.

Above all, this little experiment opened our eyes to the hidden activities of the soil, showing that you can find action, suspense, and intrigue right under your toes.

A wetland in the dry forest?

Coming from the rainy, chilly highlands of Cuericí, the climate of Palo Verde is a stark contrast.  Down here at sea level we’ve got daily high temperatures in the 80s and 90s F, and that’s with tropical sun (i.e. sunlight coming in at a near-perpendicular angle to the Earth).  At this time of year, Palo Verde is sporting a dry heat—the kind that makes your hair start to dry while you’re still in the shower, and turns popsicles into puddles in a matter of seconds.

First to welcome us to the dry forest are a group of white-faced capuchins, which we quickly learn are a common sight around the station and up in the forest’s canopy.  Not only do we have the company of the capuchins, but in the early morning, the loud, echoing calls of male howler monkeys are heard no matter where you are.  These throaty, growl-like calls that awaken the forest sound somewhere in-between a lion’s roar and a very hungry stomach.


White-faced capuchin


Nom nom nom

capuchi clique

Capuchins lounging just steps from our dormitories


Howler monkey, about to sound a call to another male


Male howler monkey leading the way through the trees


Temperature and some new mammal species aren’t the only big changes from previous locations.  Palo Verde is our first site with a wetland habitat, adjacent to its tropical dry forest.  Located downstream of the Río Tempisque is a brackish marsh, which is substantially desiccated during this dry season.  Despite its being reduced to a collection of large puddles, the marsh provides a home to waterfowl such as the roseate spoonbill, black-bellied whistling duck, Northern jacana, and black-necked stilt.  An observation tower that overlooks the marsh is just a few minutes’ walk from the station’s main campus and an excellent place to observe these species up-close—I like to go just after sunrise or in the late afternoon, when the pleasantly warm temperature is accompanied by a salty breeze.

marsh sunrise

The marsh at sunrise

marsh afternoon

The marsh at late afternoon

The first thing you notice is that the individual birds like to clump by species.  The small jacanas have claimed the shallowest part of the marsh, closest to shore.  Using their long, narrow bills, they pick at bits of floating vegetation or at the water surface and occasionally come up with a wormy-looking creature.  Further out in the marsh you’ll find the black-necked stilts, taller than the jacanas and with even narrower, needle-like bills.  Instead of just scraping the surface like the jacanas, a stilt shoves its whole bill and part of its head down into the water, rustles around for a second, and then comes up with a dripping face but no apparent prey (as it turns out, the stilts feed on aquatic invertebrates or fish, so it likely swallowed its meal while underwater.).

northern jacana

Northern jacana


Black-necked stilts

The whistling ducks are grouped together on the small islands of vegetation interspersed here and there, or slowly paddling through the marsh.  Every now and then the they’ll do the typical duck half-flip underwater, shimmy their tail feathers, and resurface.  Look a meter or two farther out and you’ll find the roseate spoonbills, tall and flamingo-pink.  Their feeding method is the most intriguing to watch—with their aptly-named bill slightly opened, they sweep it side to side just under the water’s surface.  Every now and then they find something tasty, stop mid-sweep, nibble at their prey in a flurry of splashes, and then continue on with their sweeping.

ducks and spoons

Black-bellied whistling ducks closest to front; in the back, a few roseate spoonbills


The marsh is so calm and peaceful that you would never guess what is lurking a few kilometers down the road at the source of this wetland’s water, the Río Tempisque.  Sun-bathing along the banks of the river or floating downstream as driftwood look-alikes are none other than crocodiles!  From the river’s dock you can get a nice look at these incredible reptiles—just be sure not to sit on the edge with your legs dangling…


Sun-bathing crocodile on the river bank