Top of the food chain

by Jack Ewing

Dark eyes watched from the shadows as the lone coati rustled through the leaf litter, routing up the moist soil, eating the tiny creatures it uncovered. Each step brought the raccoon-like mammal closer to the long muscular creature waiting between the buttress roots at the base of the fig tree. The coati slowly worked its way toward the tree where a climb into the upper branches would hopefully yield a meal of ripe figs. Tired of routing for grubs and insects in the dark jungle earth, the coati lifted its head, looked around and moved straight for the fig. Upon reaching the flange-like roots, it hesitated. Something was wrong.

The coati paused, wiggled its nose and sniffed, turned its head from side to side scanning the surroundings. Finally, it took another step toward the tree, followed by another pause, then another step. Like lightening the snake struck, grabbed the side of the coati's head in its mouth and wrapped the furry body firmly in its coils. The coils tightened. The coati tried to breathe, but could only exhale. Each time it expelled air from its lungs, the snake's grip tightened. Each movement of the coati produced a corresponding constriction of powerful coiled muscles. In less than a minute the coati quit struggling. A minute later the boa constrictor released its bite hold, quickly moved its head and bit down again, this time with the coati's nose pointed down the snake's throat.

The coils loosened and the boa bit down hard. With each bite, backward curving teeth pulled the prey deeper into the boa's throat. The snake's jaws unhinged and separated, opening wide for the prey to enter. Swallowing the large coati took two hours, after which the snake slept. The large boa remained inactive for eight days while its body digested the coati. Then the fearsome predator crawled off into the jungle, moving slowly, stopping occasionally, searching for the perfect place to lay patiently in ambush. It might be two or three weeks before another meal wandered within its range.

The boa constrictor ( Boa constrictor ) is Central America's longest and heaviest serpent. Though they are known to reach lengths in excess of 5 meters (16½ feet,) boas longer than 2½ meters (8 feet, 3 inches) are a real rarity. An adult coati, about the size of a Cocker Spaniel, is tough and nasty, and few predators will attempt to kill one. In Costa Rica, jaguars, pumas, and very large boas are the only ones. Boas large enough to kill and swallow a coati are seldom seen, and when they are, the experience is something to treasure.

Juan Ramón Segura, a veteran guide at Hacienda Barú National Wildlife Refuge, was with me when I saw my first large boa crawling through the rainforest on the upper slopes of Hacienda Barú National Wildlife Refuge. Fascinated by the sheer size and manner of this regal creature, we followed as it slowly but purposefully made its way through the jungle, crawling over logs as if they were mere branches, curving around trees, through leaf litter and over rocks, pausing briefly to poke its nose into every little nook and cranny. It seemed totally aware of our presence, but equally unconcerned. The boa was long and muscular, but not particularly thick. I remember thinking that its mid section was about as big around as my calf. The boa slithered effortlessly up onto a log and stretched out full length. Standing less than a meter (39 inches) away, I held a stick out toward the large reptile and measured its body length in stick lengths. Later we measured the stick with a tape. The snake was about 3.4 meters (11 feet) long. We figured it weighed more than 30 kilos (66 pounds.)

Stretched out on that log, the boa seemed totally at peace and oblivious of us, almost as if it were snoozing. We squatted down on our haunches less than an arm's length from snake, near the tail. Juan Ramón said he wanted to touch it. What do you think? he asked.

I shrugged. Go ahead if you want to. I think I'll pass. I was right beside him.

Juan Ramón lifted his hand, hesitated briefly, then gingerly reached out and brought his finger tips down on the boa's iridescent scales. Thinking back on the incident I remember the next second as a blur of rapid movement and, instantly, a golden brown head was there, hovering, a finger's length from Juan Ramón's hand, a forearm's length from his head, black forked tongue flicking in and out. The boa's head was half again as large as Juan Ramón's hand. Mesmerized, looking into the boa's black eyes, Juan slowly retracted his hand. Nobody moved. The snake watched us for a few very long seconds that seemed like minutes, turned, crawled off the log and out into the jungle. This time we didn't follow.

Later we did some serious thinking about the incident and realized that the boa was definitely big enough to kill Juan Ramón if it took a notion to do so. More than likely, it left us alone because we were too big to swallow, and until the moment of that curious contact between finger tips and scales, it hadn't considered us a threat. Simply watching this magnificent reptile filled my chest with awe. It's lack of concern about two adult humans gave the impression that it knew there was nothing in the rainforest that could harm it. Nothing would kill it, eat it or even bother it.

Wild animals, like our boa, belong to an elite group of predators that occupy a place at the top of the food chain. I imagine the position occupied by these animals as a pedestal located at the very pinnacle in the scheme of life. On that pedestal stand those animals that live by killing and eating other animals, but which are prey for none. It is worth noting that humans with weapons in hand occupy a place on that pedestal, but humans in the wilderness, with only the physical body they were born with do not.

That was the most impressive boa that I have seen, but not the largest. Surprisingly, the largest was up in a tree. My son Chris spotted it one morning by the road near our house. I leaned a ladder against a nearby branch and climbed up to take some photos. It seemed to me that the boa's enormous size and weight would prevent it from climbing, but there it was. Over half of the boa's length was stretched out on a large branch with the remainder curling around the trunk and over two smaller branches. Unlike the first boa this one was huge in girth, at least as thick as my thigh. There was a big bump in its body as thick as my waist, which I speculated might have been a recently swallowed opossum or iguana. Standing there on that ladder taking photos, it occurred to me that this boa could easily kill and swallow one of our dogs. I can only guess at the snake's length, but it was easily 4 meters (13 feet.) The boa stayed there all day but was gone the next morning. I have heard occasional reports of an enormous boa crossing the road near that spot. Two different observers said it was so long that when the head reached one shoulder of the road, the tip of the tail was still all the way across the road on the other shoulder. I feel certain that it must have been the same snake I saw in the tree. There would not likely be two boas that big in the same place.

I have heard stories from reliable observers of a couple of boas that exceeded four meters (13 feet) in length. One was killed by a cattle rancher in Uvita when he found it eating a young calf. When the rancher arrived, the calf was already dead, and the snake had swallowed most of its body. Only the hind feet were still protruding from the boa's mouth.

Most boas are welcome guests around human habitations, and play a key role in rodent control, but occasionally they can wear out their welcome. One morning I arose and went into the bathroom. My wife's cat Jamie had a litter of kittens, and they came into the bathroom mewing and huddling around my feet. That hadn't happened before, but I didn't think much about it. In the kitchen I found Jamie, wild eyed and nervous, peeking around every corner before stepping out. How odd, I thought, but went about my morning routine. Entering the laundry room, I discovered a boa, above the sink, wrapped around a rafter. That explains it, I thought. The cats sensed that there's snake in the house and are nervous about it. Then I noticed the two lumps in the boa's mid section. Wait a minute, I mused, how many kittens were huddled around my feet? Returning to the bathroom I counted three small fuzzy cats crowded into a corner. I went over to the bedroom door.

Hey honey, how many kittens does Jamie have, I called.

What are you talking about? What time is it? Diane rolled over and covered her head with a pillow.

Just tell me how many, and I'll let you sleep, I offered.

She lifted the pillow and called back , five.

Not anymore, I replied and closed the door.

It was amazing how fast she made it out of bed and to the door. What do you mean. she demanded, no sign of sleepiness now.

Come and see for yourself.

Those of you who have read Monkey's Are Made of Chocolate know about the common tree boa that lived in our attic for years and received free board in return for keeping our house free of bats and rats. Well the cat-eating boa wasn't afforded the same courtesy. It was sentenced to permanent exile and deported to a nice forested home a couple of kilometers (about a mile) from the house.

There are five different species of boa in Costa Rica. The ones described here are all of the species Boa constrictor. None of the others grow big enough to occupy a place with the top predators on that pedestal at the pinnacle of life.

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Focussed in Birdwatching Costa Rica and Ecotourism