Popular Science Monthly/Volume 84/March 1914/Tropical Nature in Colombia

From Wikisource
Jump to navigation Jump to search


By Professor A. S. PEARSE


FOR the naturalist reared in temperate climates the tropics will always be a promised land flowing-with biological milk and honey. The medical men have been pioneers in opening up this terra incognita, though they were not the first to enter it. Tropical diseases are no longer looked upon with the dread characteristic of our grandfathers, but for the most part may be as well controlled as those of cooler climates. Though there is still a small element of uncertainty to add savor to tropical exploration, the naturalist of to-day may travel to the edge of an unknown country in a modern steamship and go forth to discover new things with a complete outfit of the latest scientific equipment—if he has the money to buy it. The tropics are the same as when Bates braved the terrors of the Amazon, but modern commerce and modern medicine have made it possible to travel with more or less comfort, and such simple aids as fly dope, quinine, and mosquito netting permit one to penetrate regions which were impossible fifty years ago.

The present article attempts to describe tropical nature as it exists in northeastern Colombia along the northern end of South America, just south of the Caribbean Sea. The descriptions are based on observations made while the writer was a member of an expedition sent by the museum of zoology, University of Michigan, to explore the region about the old Spanish city of Santa Marta. This portion of South America offers unusual opportunities for zoological study on account of its diversity. A strip of sandy desert overgrown with giant cactus stretches along the coast and extends back into the interior seven or eight miles. Beyond this the foothills of the Sierra Nevadas rise; only twenty miles from the city the peaks attain a height of 8,300 feet above sea level. Many small streams take origin in the mountains and unite to make their way across the lowlands to the coast. Extensive mangrove swamps line the shores of the Cienaga Grande, a great lagoon into which several rivers empty.

The members of the expedition were met as they stepped on Colombian soil by Mr. William A. Trout, the American consul at Santa Marta, Mr. M. A. Carriker, and Mr. O. Flye. These gentlemen and their families did everything they could to make our stay pleasant and profitable. The Colombian government was also extremely courteous, allowing our outfit to pass the customs without inspection.

Strangler Trees. The figure at the left shows a young strangler, that at the right shows an old one. The tree about which the latter wrapped itself was killed and has rotted away.

Starting the day after our arrival we rode eighteen miles into the interior on mule back to the Cincinnati coffee plantation, the home of Mr. Flye. That ride was wonderful! As we went higher the luxuriance of the vegetation increased and the trail often hugged the brink of a precipice where one could look for miles over the virgin forest and banana plantations below. Like the hunter in the "Lady of the Lake," we

often paused, so strange the road,
So wondrous were the scenes it showed.

We lived at the plantation for a month in a clean little adobe house at an altitude of 4,500 feet. In half a day we could walk down to Minca, at about 2,000 feet, or up to the top of San Lorenzo, 8,300 feet. Beyond the coffee the tropical forest stretched away, unbroken; in one direction to the desert along the coast, in the other toward the snow peaks at the crest of the Sierras. Every afternoon it was cloudy, usually there was rain.


The Tropical Rain Forest

Two things are noteworthy in comparing tropical forests with those of colder regions: the diversity of the vegetation, and the intensity of the struggle for existence. In the temperate or frigid regions of the earth which are forested we are accustomed to see one species or genus of trees dominate all other plants and become a "climax forest," e. g., oak, pine, spruce, beech forests. But in the tropics conditions are favorable for many species; the growing season is always good, and the forest is always varied. Tree ferns, palms, vines, deciduous trees, epiphytes, mosses, ferns—all grow in riotous confusion. Vines climb over great

A Tree Fern.

trees and steal their sunlight; strangler trees grapple with forest giants, squeeze them out of existence, and take their places; epiphytes and mosses festoon the limbs of trees, stretching their leaves toward the light that filters through the canopy above. Any handicap means that a tree must give way to more successful rivals, and many drop out. But the floor of the forest is not always strewn with the remains of the unsuccessful, for where it is not too wet the termites, or white ants, honeycomb every bit of dead timber and convert it into powder, which in turn is soon "resolved to earth again." Thus the cycle goes round and tree succeeds tree. One who lives in a temperate climate has no idea of the manifold intensity of the struggle among the plants in tropical forests.

In the midst of such a struggle one would expect to find a great variety of adaptations for surviving, and such is indeed the case. Many trees have wide props or buttresses extending out from their bases which stiffen them against the fury of tropical storms. Some trees have thick bark which is scaled, or smooth, or ridged, or ringed, or spiny, or what-not; some scarcely have bark at all, but are smooth and naked. Palms not only grow in the conventional form, but many masquerade as climbing vines or epiphytes. Everywhere there is specialization and adaptation along many lines.

The humid shade of the forest offers shelter to many animals which, like the plants, show a great variety of adaptations. A large number of animals depend directly on the plants for food. The lowly termites are quick to appropriate any dead or diseased parts; vegetarian ants swarm everywhere. Long-tailed Kinkajous come forth at night to climb about in the mango trees; wood rats, squirrels and agoutis feed upon the. luscious aguacates (“alligator pears”). Many birds have become specialized for fruit eating: flocks of gaudy parrots squawk among the trees, resplendent toucans wipe their great beaks against the limbs which have borne their repasts. In addition to these specialists many other birds eat fruit when it is available: trogons flit shyly here and there, and conceited motmots perch so that they may proudly wag their beautiful tails from side to side. Yet the denizens of the tropical forest do not appear gaudy and highly colored. A parrot is indeed a splendid object when you hold him in your hand, but stand below a mango tree and you are amazed to find that it is practically impossible to see any of the flock which are squawking noisily through its foliage. Only by watching carefully for movement can you pick out a bird here and there.

Besides the animals which hunt in the trees many wander about over the ground beneath. These are usually not brightly colored. Tapirs were common about the plantation, and one was killed by the workmen during our stay. These pachyderms had regular trails like cow paths through the forest. Droves of peccaries rooted in the ground and we often saw places where they had been feeding, but that was all. Mr. Flye told us how he had once been treed by a drove of these ferocious “wild hogs” which stood about and gnashed their teeth for a couple of hours. Jaguars and tiger cats hunted in the forest. One day a small boy brought us an armadillo. Agoutis were common everywhere. Once, while I rested at the fork of a river a great agouti came to drink fifty feet below. My Colt was at my hip, but I did not have the heart to shoot him—so much at ease was he, so self-contained, and so in keeping with his forest. He took his drink and went away, never knowing that a strange gringo had watched. Another time we saw a troup of big red monkeys swinging along through the tops of the trees, but they quickly scampered away when they spied us. We always went armed with gun or pistol hoping that we might bag one of the larger mammals, but fate was against us. The large animals are extremely shy and their coloration

A Termite's Nest in a Tree. Note the covered roadway passing down the tree trunk which bears the nest. The figure at the right shows the covered roadways of termites on a tree trunk.

makes them difficult to see. To secure them one must attend to little else. Our interests were not in big game, but we were well repaid with smaller fry—the forest filled our eyes, and notebooks, and photographic films to overflowing—yet never to satiety. There was always something new and interesting.

The forest swarmed with lizards, such as the little anoles and geckos, which crouched motionless or scampered swiftly after fleeing insects. Snakes lurked among the fallen leaves or climbed among the trees—gaudy coral snakes with their cross bands of red and yellow, the vicious fer-de-lance or bushmaster (called "Ecke" by the Colombians), big, but harmless, gopher snakes. Sometimes we met a "Bejuca" (vine snake)—the most curious of them all—never half an inch in diameter and attaining a length of three or four feet. But snakes were not easy to find. We rarely got more than two or three in a day, sometimes one, often none. Scorpions, tarantulas and other spiders abounded throughout the forest. Big land snails crawled on the trees or over the ground. Bright-colored butterflies fluttered in flocks through the open spaces. Probably the most typical forest vertebrates were the little tree frogs, which were abundant and various, and whose shrill piping was often the only sound to break the deep silence.

At night we took our jack-light (an acetylene lamp mounted on the front of a hat or carried in the hand) and sought nocturnal animals. On these excursions Bufo marinus, "the giant among toads," was always encountered. Another curious toad, a Ceratophrys, was dubbed the "snapdragon" by Dr. Ruthven on account of its fierce behavior. It would snap at us and grasp the end of a stick in its mouth, hanging on firmly while it was swung about in the air. Goatsuckers and bats often came right up to the light and flew about over our heads. Snakes were active too, and we often flashed the light on one of them, hunting in the night.

Under fallen logs we found an admirable hunting ground for various invertebrates. Land crabs were often unearthed at considerable distances from the water. Centipeds of all sizes were abundant, some of them twelve to thirteen inches in length. Many millipeds and centipeds were found in their little nests where they lay eggs and rear young. Some of these nests were simple hollows in the soft pulp of rotting logs, others were carefully made dome-like structures formed from little pellets of mud. But the greatest find under fallen logs was the curious Peripatus, a primitive arthropod which resembles the segmented worms in many characteristics. These beautiful velvety animals glide slowly along, feeling their way with the two antennae at the anterior end. If touched, they turn about and squirt two viscid threads from beneath the head. These threads, which harden quickly, serve to capture prey or entangle aggressors.

Termites were abundant in dry places everywhere up to an altitude of about 5,000 feet. They never come out into the light, but always construct covered galleries of wood-dust, dirt, excrement, etc., wherever they go. Some species live in the ground and build great mounds over old stumps and logs; others make mud nests on tree trunks from which they build galleries in various directions. These insects live in great colonies in which there are usually several enormous egg-laying queens and thousands of workers and soldiers. They eat away a piece of wood so that the interior is converted into a powder while the exterior is perfect. A log is thus reduced to a thin shell which crumbles at a touch.

Probably the most characteristic and interesting animals in tropical

Termite Nests in a Field.

A Termite's Nest on a Dead Tree. Note that a woodpecker has made a hole near the top.

forests are the ants. Attention is at once attracted to the leaf-cutters which toil ceaselessly through the night and during most of the day, only intermitting their labors during the hottest part of the afternoon. These ants make big mounds, sometimes twenty feet in diameter, with numerous entrances. The underground galleries' are continually extended and modified for there is an excavating party at each mound which carries little particles to a particular spot at some distance from the

Foraging Ants Crossing the Trail.

entrance where there is a dump pile. Other individuals of the colony are constantly moving along pathways in the forest carrying pieces of leaves. The same paths are evidently used for a long time as they may be six inches wide and worn (by the ants and rains) to an inch or two below the surface of the ground. An ant cuts a bit of a leaf, using his mandibles like a pair of scissors, and carries it into the nest. Here the leaf fragments are chewed into a pulp, spread out in beds, and planted with fungus. The sole food of leaf-cutters consists of fungus raised on vegetable pulp.

The driver ants go through the forest in great swarms cleaning up all the small live things as they travel. They have no home or permanent

In the left-hand figure the white mass is a fungus garden of a leaf-cutting ant. The thorns shown at the right are occupied by small ants. Note the small opening which leads into the cavity within each pair of thorns.

abiding place, but carry their eggs, pupae and food with them. There is never any doubt when drivers are at hand, for all the sow-bugs, crickets, and other small creatures which usually hide in crevices are out in the open hopping hither and thither in frantic efforts to escape. The drivers we saw were small blind black ants which formed a veritable carpet over everything as they progressed. They covered the ground, searching every nook and cranny; they climbed each tree, slowly, methodically, carefully; they left no place unexplored; next day they were gone.

The foraging ants are somewhat like the drivers. They are larger and many individuals have great white heads provided with a pair of

In a Banana Plantation. Each tree is cut down when its single hunch of fruit is harvested, but new sprouts grow up from the root. 500,000, bunches of bananas are shipped from Santa Malta each month for New York.

enormous recurved mandibles. Like the drivers, these ants carry all their impedimenta with them. Those we observed always traveled in narrow columns which flowed ahead like living streamlets, branching out and reuniting over and over again. Foragers always appear to be in great haste and go scuttling along carrying pupæ, larvæ, pieces of dismembered insects, spoil from the nests of other species of ants, etc. We saw some foragers form long covered lanes with their bodies by clinging to each other with their mandibles and legs. Through these covered roads other individuals of the swarm scooted along—these were robbers carrying booty from the nests of other ants.

A Bromeliad.

Many ants manufactured a sort of dirty paper from which they built hanging nests in trees. Others excavated logs like termites. One of these Mr. Gaige, our ant man, called the “spread-eagle nipper.” This was a big black ant which opened its mandibles so wide that they stood out straight at the sides of the head, and then brought them together with a snap that could be distinctly heard at a distance of several feet. Woe to the unwary finger that was between those mandibles when they came together!

At Fundacion, a village in the forest beyond the banana country, we discovered two curious species of ants living in trees. One of these built little paper sheds over aphids which it put out to “graze” in the acacia trees. The aphids sucked the juice from the trees and gave out a sweet secretion which was taken from their bodies by the ants. The other species mentioned lived in little hollow thorns on the branches of an acacia. This tree was a true ant plant for it grew the hollow thorns in pairs with a little doorway leading into the cavity within them. The doorways were present in young thorns even before the ants had occupied them.

We can not pass the forest without mentioning the bromeliads. These plants are members of the pineapple family and are much like pineapple plant without the “apple” at the bottom. High up in the mountains they grow on the ground, but as the altitude grows less they begin to climb upward, and in the lowlands live as epiphytes in the trees. The bases of the leaves interlock in such a way that they make tight cups which act as reservoirs for the water that runs down from the tips of the leaves. The water contained in one of these plants frequently totals to two or three quarts, and the thirsty traveler is often glad to make use of it. Many small animals pass their lives in the shelter of bromeliads. We found tree frogs with their eggs, dragon fly larvae, rat-tail (fly) larvæ, beetles, cockroaches, spiders, salamanders, and many other small animals. We tore open logs for two weeks and found only two salamanders, but got twenty from the bromeliads in a single morning.

The Desert

The strip of sandy country near the shore of the Caribbean Sea grows cactus and various xerophytic shrubs. Many of the cacti are thirty feet tall. Here the most characteristic animals are the ground lizards which swarm over the sand everywhere. Many of these are brightly colored with yellow or blue.

We were surprised to find land snails quite abundant in the desert. At the time of our visit they were activating in the crevices of curiously twisted trunks of the small acacia trees. Here also we occasionally found a land tortoise (Testudo labulata) wandering about among the cactus. Several streams ran through the desert. Near these the little

Desert Snails Aestivating in the Twisted Trunk of a Desert Tree. Mangrove Seeds.

conical pits of ant lions often covered the ground so thickly that it was impossible to avoid walking on them.

Once near the sea we came across a great number of terrestrial hermit crabs, Cenobita diogenes, each encased in the shell of a land snail. The little army was moving slowly through a rocky portion of the desert where its members could sidle quickly from the shelter of one rock to that of another. These little crabs live a truly terrestrial life, and return to the ocean only once a year, when they breed. They apparently require very little water, for I brought three home with me and they have lived in a dish of dry sand in my office for more than six months. They have of course been supplied with food and a small cup of drinking water.

This desert, like those in other parts of the world, has a rather sparse fauna consisting of a few species, most of which are able to stand extreme desiccation, long fasts and great heat. The lizards and tortoises with their dry, scaly skins, the land hermits with thick exoskeletons and borrowed shells, the land snails with thick calcareous coverings, are all admirably suited to desert conditions.

Brooks and Rivers

The streams on the northern Colombian coastal slope are easily divisible into two classes—mountain torrents and rather slow-flowing meandering rivers. From headwaters in the mountains the water rushes down over rocky beds for a time, then comes abruptly to the level sandy plain where much of its impetus is soon lost.

The most striking characteristic of the animals of the mountain torrents is their ability to hold on. The little catfish found there have a free spine on the pectoral fins which enables them to cling tightly to the rocks; the caddis fly larvae are all fastened firmly by threads; the water bugs are greatly flattened so that when they cling to a rock their bodies offer little resistance to the water. On the surface of the brooks enormous hairy spiders with ridiculously small bodies hunt for a living.

The tree frogs in the mountains were hard pushed to find a place to breed, for there was no standing water on the ground. They either carried their eggs on their backs or laid them in the bases of bromeliads. Many of the aquatic animals which are characteristic in other parts of the world are lacking in the mountain streams. There were no snails, pill bugs, or amphipods. The fauna was a specialized one—limited mostly by its ability to avoid being swept away.

In the slow rivers of the lowlands the most characteristic animals were the shrimps and prawns which often possessed greatly elongated claws. Curious little shrimps belonging to the family Atyidæ were quite common. These crustaceans have the first two pairs of legs modified into little brush-like forceps with which they scrape the microorganisms from the soft bottom or from aquatic plants. Many land and freshwater crabs lived along the shores of the rivers. Among these Cardiosoma guahumi was most conspicuous on account of its blue color and large size. This big crab digs holes in the mud beneath the trees near the mouths of rivers. It comes out at night seeking food and climbs the trees to eat the leaves. It was a great sight to watch hundreds of these crustaceans on the mud flats, sitting motionless in the glare of the jack-light.

Along all the streams below 2,500 feet there were many lizards of the genus Basiliscus. These animals have a very long slender tail and small front legs. When disturbed they stand nearly upright and run swiftly over the surface of the water, using only the hind legs and the tail, like the ancient dinosaurs. In the trees along the rivers we encountered many iguanas. These big lizards sit in the trees and if disturbed often

A Land Crab, Cardiosoma guahaumi.
Mangroves Growing at the Edge of the Cienaga Grande

dive from a height of thirty feet or forty feet into the water, swim underneath the surface to the opposite bank, crawl out and hide. We shot one iguana that measured 4 feet 91/4 inches in length.


Many of the plants which are raised in hothouses or summer gardens in the United States are common weeds in Colombia. In the forest calladiums and cannas grown everywhere; umbrella plants line the shores of all the streams; in the swamps cannas and umbrella plants

The Ford at Minca, at an Altitude of about 2,000 Feet.

constitute an important part of the flora. In some swamps there was a slender stemmed plant which had little white air bladders to keep it at the surface.

The jacana, a rail-like bird, is admirably adapted to live in tropical swamps. The greatly elongated toes enable this bird to walk with ease over the floating vegetation. Both sexes have a spur on the front of each wing which they use in fighting. A flock of jacanas is a beautiful sight as it alights, for every bird stretches its yellow-tipped wings as far upward as possible before closing them. Another swamp bird was a

Giant Cactus and Desert Trees.

species of tree-creeper which built a long bottle-shaped nest, which was constructed of thorny twigs in low shrubs. The eggs were placed in a little enlargement at the closed end and the long thorny entrance prevented snakes and other predaceous animals from entering.

The swamp water swarmed with aquatic bugs, beetles, snails and other animals. One large snail always climbed out of the water to deposit its beautiful rose-pink cluster of eggs on the stems of plants. Around the margins of the swamps there were many land crabs, snakes and peculiar engistomatid| toads. Tropical swamps constitute an admirable habitat for many animals. The abundant vegetation and small animals fill the water with an organic network which supports many larger predaceous animals such as fish, herons, ducks, jacanas and snipe.

Mangrove Swamps

Mangroves are found only along the muddy shores of salt or brackish water in the tropics. These peculiar trees play an important part in land formation in such places for they keep growing farther and farther into the water and the accumulation about their roots makes new land. They are admirably adapted to live in mud flats. Roots branch out from the trunk in every direction and keep it upright on the soft bottom. The seeds germinate before they drop off, each forming a long spike like root which penetrates the mud so that it is not washed away after it falls. Roots are sent along just beneath the surface of the mud and many small aerial rootlets grow upward from these which enable the

Mangrove Swamp. Prop roots support the small tree in the foreground and are growing down from the large tree further back. Many aerial roots are sticking up from the mud.

mangroves to survive in the salty water of the foul mud flats by absorbing substances from the atmosphere.

In the mangrove swamps along the Colombian coast we had a most exciting time. Mr. Trout towed our bongo (dug-out canoe) out on the Cienaga Grande, a large estuary, with his launch, and we spent several days at the edge of the mangroves. At night we were obliged to pull out into the middle of the Cienaga, for the mosquitoes were unbearable. One evening a vampire bat took the liberty of biting one of the party on the top of the head while he slept. Two of us had been hunting with jack-lights and on returning found him with his hair full of blood. Often half a dozen of these little bats would settle over the roof of the boat after dark and compel us to move elsewhere to sleep.

Fiddler crabs swarmed among the aerial roots of the mangroves and Sesarma crabs climbed about over the prop roots and trunks. Crocodiles fished along the shore and the slapping of their tails was often the last sound we heard at night. Among the trees there were thousands of herons and many cormorants; sandpipers swarmed along the shores of the lagoons. Occasionally we met rarer birds, such as the beautiful roseate spoonbill.

Back of the mangroves along the shores of the Cienaga Grande we had our best jack-lighting. As the light moved along the eyes of the raccoons glowed like pairs of fiery cherries, now and then a deer crashed in the brush, and occasionally a big ant-bear lumbered away through the dark. Shooting at night is not easy. There is no target but the shining eye of an animal. Nevertheless, Mr. Trout shot a fine buck deer and a seven-foot crocodile. The former was hit in the center of the forehead, the latter, though shot from a canoe, was pierced cleanly through one eye.

In closing I must speak of my two companions, Dr. A. G. Kuthven and Mr. F. M. Gaige. It is no small test of friendship to be with two other men day and night for three months in a strange country. One has an excellent chance to become tired of his companions. But these gentlemen were so cheerfully unselfish in bending every energy to further the cause of science by making the expedition a success, so patient during the trials which always come in a tropical climate, that, though I had known and liked both for years, I came back home with increased admiration and respect for them.