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Lessons in Patience

Frog Eggs, Snakes, and Rain

In my memory of 1992, there was no rain at Sirena Biological Station, in Corcovado Park, Costa Rica, until the 19th of July. My journal reveals that is wrong. I noted sprinkles, drizzles, and even 22 mm one day, none of which filled the frog ponds. In that rainforest—where 10 cm of rain often fell in a day and about 5 m in a year—it took a serious downpour to get the frog reproductive season started. My memories of rain are emotionally aligned with the frogs’ needs.

I had been to Sirena a year earlier, on a field course, looking for an interesting frog and a research question that would let me live in the rainforest, studying eggs or tadpoles for my doctorate. At night, I had seen Cat-Eyed Snakes (Leptodeira ornata) eating the beautiful, transparent eggs of Red-Eyed Treefrogs (Agalychnis callidryas) hanging on leaves over a pond. I had also seen a few embryos hatch, after I accidentally bumped an egg mass. It was quick enough that I began to wonder if they might be able to escape from egg-eating snakes. Back in Texas for classes, I spent months discussing my escape-hatching hypothesis with other scientists, some intrigued and others dismissive. As the field season approached, I carefully planned my experiments, hoping to see snakes try to eat embryos that might be able to hatch. Did I have a novel idea worth testing and the start of a dissertation project? Or just an overactive imagination and no tractable research plan? The snakes and eggs would tell me.

I knew the Agalychnis pond in Sirena had enough egg-eating snakes for my work, but watching them feed would be another matter. The sometimes-rapid movements of snakes belie their immense capacity for stillness. Even Cat-Eyed Snakes, actively searching the vegetation for eggs, spend long periods immobile. On the field course, standing hip deep in the pond in the rain at night, waiting for a snake to move, I had wondered if I really had enough patience to work with them. I knew I would need new snake-watching skills to test my hypothesis, but when I returned to Sirena I encountered an unexpected challenge. The pond was dry. No place for frogs to breed meant no eggs for snakes to eat and no way for me to answer my questions. Still, it was 18 June, so it should rain soon. Expecting a downpour any day, I set up my handcrafted snake cages and prepared to start my research as soon as there were eggs.

Sirena station housed park staff, biology students, and ecotourists amid the amazing wildlife of the largest protected patch of lowland Pacific rainforest in Central America. My tent was pitched in the unwalled second floor of the main building, under a tin roof that would amplify every raindrop—if rain fell. I woke each morning to a raucous chorus of Scarlet Macaws drawn near by a young bird, rescued from poachers, who still roosted in the building. At first, I delighted in long walks, getting to know the forest, beach, and intertidal. I saw so many crabs—robust land crabs that emerged from burrows to wander the forest floor at night; hermit crabs in their mollusk shells, clustered on fallen fruit at the top of the beach; alert orange fiddler crabs scuttling to their burrows when I approached. As the rainless days continued, I thought about studying crabs instead of frog embryos. I could have been working, testing a hypothesis already, like the other biologists. To feel like a scientist, I helped count and measure palms, photograph lizards, watch butterflies, making tiny contributions to other people’s work.

Still, I was not alone in my frustrated desires. The hungry snakes and sexless frogs shared my powerlessness to affect the one thing that mattered. When would it rain? My Corcovado journal reveals our shared stress and my peculiarly human responses.

Sirena Station, 6 July 1992—Rain structures our lives, here in this rainforest. Or, at the moment, lack of rain. Lack of rain keeps my frogs up in the trees, males calling futilely from dry ponds, snakes first searching and now only waiting for eggs that don’t come. Lack of rain maintains this oppressive heat and my constant sweating, even seated immobile, only writing. Here, we become more superstitious. So much of our lives are beyond our control, at the mercy of the forest and its creatures. We develop rituals that allow us to believe that we have some control, that what we do matters. We joke about the mosquito gods and the cult of the coil. We joke too about the rain, but still we leave our laundry out and go without umbrellas, hoping for rain, or always carry umbrellas, hoping for lack of rain. When by chance the rain fits our superstitions we point it out. You left your laundry out? Of course it’s raining. In reality, the rain gods pay us no heed, preoccupied with their own agenda in this El Niño year. I repeat my laundry-hanging rituals in vain, hoping for the half-bucket rain that will bring my frogs down from the treetops, waiting for a chance to work in this place of tourist holidays.

As Sirena continued to be—by egg standards—rainless, I lived with uncertainty. Could the embryos really be capable of assessing risk and fleeing from danger? It seemed far-fetched but also logical, among so many hungry snakes. Or, was I just wasting time and resources, as some had suggested? No eggs meant no data and no answers. To fill the waiting, I left for a few days, hiking inland across the park.

Los Patos Station—The red mud has only enough moisture to be sticky. Thick and hard it catches my boots, snaps sounding at every step as I break its grip on my feet. We walk all day in the heat, sweat sliding down our surfaces, soaking our clothes and starting to ferment. Sometimes I wipe my arms with a bandana. It gives a moment’s coolness, a few seconds respite before the beads congeal into one smooth layer and I stay wet as in a bathtub, my skin softening and wrinkling in its own water.

At 1:30 it rains. The first drops fall on the canopy and are consumed by foliage, reaching us only in sound. Fifteen minutes later, water arrives to the ground and its creatures, dripping through layers of leaves, accumulating on drip-tips, splattering on the trail. My sweat is diluted by the splatters and, somewhat less than body temperature, they cool me. I relax in the knowledge that everything in my pack that is still dry is sealed in Ziplock bags. (I don’t think about the clothes molding in two days of sweat and mud.) Rain soaks the leaf litter but the red mud resists its passage. Only the top layer softens to slickness, water accumulating in red puddles on the trail. On the hills it flows from footstep to footstep in red waterfalls. Puddle, waterfall, puddle, waterfall, I make my way. The splashes raised by the hiker in front of me will be permanent red stains on my off-white field pants.

When I returned to Sirena, the ponds were still dry. Advised that a watched pond never fills, I left again, walking northwest along the beach to the amazing Llorona Plateau, home to the largest trees in Central America.

Llorona Beach—The beach is covered in orange crabs feeding on intertidal sand, two pointed eyes on stalks watching warily as I approach. The occasional wave that comes farther up sends them scurrying, concentrating a line of more intense orange along its front. A splendid sight. I think of fiddler crabs as having rounded eyes, the stalks bulbous on the ends. These creatures have pointed eyes, topped with a bright orange spike, a sort of clown eyebrow for crabs. It gives them a perpetually surprised expression. Walking here last night, I was expecting crabs, the whole beach littered with lumps of crab-chewed sand. The walk was beautiful: wide wide tidal flats, soft wet sand glistening with the moon’s reflection, the occasional plover or sandpiper flushed unseen, piping before us, and the white edges of the waves breaking far out to sea. Higher on the beach, before the Rio Corcovado, we crossed cat tracks. First two sets together, large and round enough to be jaguar. These were fresh, and so close to the falling tide line we must have been within half an hour of their makers. Probably our paths crossed in the dark, and they saw us but not we them. Later we saw even bigger tracks, a solitary individual, and a set of smaller ones, probably margay. It seems the beach is full of cats.

Returning from the wonder of Llorona to dry Sirena, I was tired, blistered, and miserable. Was my egg project doomed? Should I try to study crabs? The frogs and snakes had no choice and, with them, I continued waiting for rain. Then on 19 July our luck changed.

Sirena, 19 July, ~10 p.m.—Perhaps, finally, the days of half-bucket rains are upon us. It started raining, really, at about 5:30, and it’s raining still. I emptied the rain gauge at 9:45 and it was already 88.2 mm. I’ve been saying 10 cm is what we need to fill the ponds and get some frog action happening. And it looks like we’ve got it. The drainage ditch across the airstrip has water, as do the grass flats. The streams are up, the Naranjo-beach pond is hip deep, and my pond is gathering water and frogs rapidly. The frogs were just bouncing in as I sat there. Finally! It’s been a long dry season.

The wet places of Sirena were a frenzy of frogs, an orchestra of nine species calling, an intense convergence of mate-seeking females, laden with eggs, hastily migrating from forest to chorus.

Wading in the ponds, I am reminded of the joys of being wet to the crotch in rubber boots full of water and tapir shit, of shivering, insect bitten, coughing from breathing in bugs attracted to my headlamp, while trying to keep track of amplectant pairs. Yes, this is what I am here for! This is the true happiness of a crazed herpetologist.

12:30 a.m.—The rain had quieted down but now is back with a vengeance. We must have 15 cm. So much water is blowing around that my tent, under the station roof, is getting wet. There was a drip, a splash onto my face. Perhaps this awakened me. This or the thunder. Finally it really is raining. Finally I have opportunity and reason to go in over the tops of my boots. This thunder is music to my ears. The splatters of rain into my tent are kisses. I feel great vicarious delight in the frogs’ good fortune. It has been a long dry season.

And it rains, it rains. The lightning and thunder are almost continuous; the building shakes and I smile. This is it, the turning point. This morning I woke, after two days of gloom and despair, in an excellent mood. And for no reason, I thought. I just felt, no matter if the rain is taking its own sweet time, it is right for me to be here; I am learning things. And now, the rain comes. Is it because I loosened my desire? Was my inexplicable happiness simply a foreshadowing of this wondrous night, finally wet again? It does not matter. What matters is only that it rains, frogs call and mate, and the life cycles of the wet ones continue. I am privileged to be here, to see it. Life is good. The frogs and I are enjoying this night. They out in the wet and me, no longer shivering, in my tent watching the play of lightening in the sky and seeing again the plop, hop, splash of frogs coming out of the forest to the pond, frog by frog by frog. The rain is so loud it drowns out the sound of their calls. Amazing.

This night at the Agalychnis pond, my pond, the snoring chorus of Milky Treefrogs was so loud I could only hear the Agalychnis in the lulls between snoring. I don’t know if the Agalychnis only call in the lulls or I just cannot hear them over the snores. Their little clucks are pretty quiet. But they were there first. They have been waiting a long time for this night.

The next night Agalychnis festooned the plants with egg masses, and I began my life of repetitive egg counting. At the pond, I checked clutches twice daily until all the embryos disappeared, hanging cups underneath to catch hatchlings and determine how many eggs survived to become tadpoles. In experiments, I used cages with removable dividers to control when snakes could reach eggs and observe predation on late-stage embryos. The snakes continued to test—and train—my patience. I learned to move slowly and silently, working in dim light, to check for snake activity and count experimental eggs. I learned to count eggs often until a snake awoke—some soon after dark, others not until 3 a.m.—for a baseline, then take extreme care, freezing if the snake moved, until it began feeding. Once they had a mouthful of eggs, the snakes seemed to shift focus and would continue feeding while I watched. After I spent many nights sitting in near darkness, watching them eat, some would continue feeding through camera flashes. This gave me the first photographic evidence to support what my egg-count data also showed: at later developmental stages, Red-Eyed Treefrog embryos do hatch in response to snake attacks, and most escape. This became the basis of my doctoral dissertation and my entire research career.

Twenty-four years later, in Panama with students, I set up a wasp-feeding station for an undergraduate to video-record escape hatching. Walking slowly through the nearby pond, holding a leaf with young eggs and looking for egg-eating wasps to recruit for our experiment, I encountered a lovely green Parrot Snake (Leptophis ahaetulla). This normally skittish species is the only snake we know that eats Red-Eyed Treefrog eggs in daylight. This individual seemed unusually calm, so I started recording video; it did not flee. I extended the eggs-on-a-leaf, then held as still as I could. The snake tongue-flicked and slowly approached as my student watched. The video shows a close-up of the snake eating eggs from the leaf in my hand. After a few minutes, under the sound of birds and insects calling, there are quiet human voices. First, scientifically, discussing the snake’s feeding behavior. Then, my understated wonder: This is pretty amazing. I’ve never hand-fed one before. Really? Yeah. Wow, I thought this was like your millionth time. No. This was unique, but even after 30 years working with egg-eating snakes, every snake encounter in the wild feels like a gift. The rain and the beautiful eggs it brings are gifts, too, that the snakes and I share.