Dominical Costa Rica

FISH, MEAT, FRUIT, NECTAR, BUGS OR BLOOD
WHAT STRIKES YOUR FANCY

   What is 9 cm long and 70 cm wide, travels at speeds of up to 30 km per hour, is found near water, has a face like a bulldog, prefers to work shrouded in darkness, and eats fish? If you guessed that it was a Noctilio leporinus, you score 100%.
   The first time I saw the greater fishing bat, was early one morning just before daybreak. I was waiting near a roosting site for water birds. I wanted to experience mass confusion of wings and feathers when the boat-billed heron (Cochlearius cochlearius,) a nocturnal species returned to roost, and the cattle egret (Bubulcus ibis,) a diurnal species, flew off to feed. As the first glint of sunlight penetrated the darkness of the mangroves, I noticed a shadow skimming over the surface of some open water. As the light of day slowly diluted the darkness, the form of a large bat became visible. It swooped down, skimmed along the surface of the pool, then pulled up and banked sharply to avoid colliding with the mangrove trees on the far side. On the next pass the water rippled momentarily when the bat’s feet hit the glassy surface. It pulled up with a minnow-sized fish in its strong claws and flew away, presumedly back to the roost.
   A few years later, in the late 1980s, I got to see a fishing bat up close. A team of biologists, specializing in bat studies, were working at Hacienda Barú. The three scientists from Erlangen University in Germany, were trying to identify the various bat species of our zone. Their work consisted of capturing bats in mist nets, identifying and photographing them, and then releasing them. The biologists also took weights and measurements. One of the first specimens they caught was a greater fishing bat. When I looked at this bat’s face up close, I clearly understood the origin of its nickname name, the bulldog bat. The long lips and shape of the head is striking. Otto Helverson, the team leader, showed me its large feet and curved claws, perfectly formed for snatching slippery fish from the water. He extended its long wings. At 70 cm, the fishing bat’s wingspan is one of the widest in the bat family.
   I asked Otto if we were likely to catch any bats larger than the bulldog bat. “We may find some that weigh more,” he replied, “but none will exceed its wingspan. There is one bat that weighs over twice as much and has about the same wingspan, but I have never seen it. Maybe someday I’ll get lucky.”
Otto’s lucky day wasn’t long in coming. Two nights later, in the primary forest of the upper slopes of Hacienda Barú National Wildlife Refuge, they netted a beautiful specimen of America’s largest bat, the false vampire bat (Vampirium spectrum.) It was so named because early investigators, saw its large sharp teeth, assumed that it was a vampire and classified it as such. Later it was found to be carnivorous. It feeds on birds, small mammals and other bats. After catching the false vampire bat, the German biologists decided to keep it until morning when they would complete their examination. Vampirium spectrum spent the night in a small tent next to the scientists. Prior to netting the large carnivorous bat they had placed two other bats in the same small tent where they decided to hold Vampirium. These unfortunate creatures became supper for the carnivore, and Otto’s team were kept awake during the rest of the night, by the sound of crunching bones. In the morning not even a hair was left of the two smaller bats.
   The bat specialists also captured several specimens of the common vampire bat (Desmodus rotundus,) a true blood feeder. They explained that common vampire bats are agile on the ground as well as in the air. They are adept at crawling, climbing and hopping, talents that they use to approach their sleeping prey after landing a short distance away. This species has razor sharp incisors which it uses to make a small cut on the victim, often on the back of the neck. The scalpel-like edge of these teeth allows the bat to perform this task without awakening the prey. As blood begins to flow from the wound the vampire laps it up with its tongue. At the same time, it secretes saliva containing anticoagulants that impede clotting. This causes the blood to flow freely. Once the bat drinks its fill, about half a shot glass of blood, it flies away leaving the sleeping prey with an open wound, bleeding freely. Since vampire bats, eat only blood they are unique in being the only true parasitic mammals.
   We once found a colony of common vampire bats roosting in a large hollow tree in the Hacienda Barú rainforest. The smell of ammonia was overwhelming. Accustomed to seeing a fine powdery guano in bat roosts, I was puzzled by the sticky, slimy substance on the floors and sides of the hollow trunk. I later learned that this is a definite sign of a Desmodus roost. Their blood diet is low in carbohydrate and fat and high in nitrogen rich protein, which produces the ammonia smell. On several occasions I stuck my head into that hollow tree, illuminated the bats, and even took photos. They never showed any sign of aggressiveness and made no attempt to bite me. Apparently true to vampire lore, nightime is when they do their thing. They tend to avoid the light of the full moon, only venturing out on the darkest nights. Ecologically this may be an indication that common vampire bats are vulnerable to attack by nocturnal predators like night hawks and owls.
   In temperate climates such as North America and Europe, bats are exclusively insect feeders, but tropical bats eat many other things. During the week that they worked at Hacienda Barú Otto and his colleagues identified 23 different species of bats. These included 1 fishing bat, 1 carnivorous bat, 1 blood feeding bat, 1 frog eating bat, 3 omnivorous bats (fruit, nectar, insects,) 1 exclusively nectar eating bat, 7 insect bats and 8 fruit bats. The German biologists have returned to Hacienda Barú from time to time, increasing the list by a few more species on each visit. To date they have identified a total of 33 different kinds of these furry flying mammals. Otto commented that as many as 100 species of bats may frequent the nightime skies around Dominical.
   In the tropics bats display the same diversity typical as so many other types of rainforest life. The smallest bat captured by Otto’s group weighed only 4 grams, about the same as a 100 colon coin. The false vampire was the largest at 200 gm, as much as a Big Mac with double cheese. Wingspans varied from as little as 15 cm, the length of a 1000 colon bill, to as much as 70 cm, the length of your arm from shoulder to fingertips. The nectar bat (Glossphaga alticola) has the longest tongue, 5 cm, almost as long as its body. The common vampire has the sharpest teeth, the long-eared bat the longest ears and the leaf nosed bats the longest noses. But the prize for the ugliest bat definitely goes to the wrinkle-faced bat, no doubt about it.
   One of the last bats we added to our Hacienda Barú list is certainly one of the strangest. One day while on a guided tour we were watching a group of monkeys playing in some native royal palm trees. One of the visitors sighted a white bat. At the time I assumed it was an albino. Disturbed by the monkeys, the bat flew away before we could get a good look. The next day I returned to the site with Juan Ramón, one of our guides. We found the white bat hanging under the same palm leaf where it had been a day earlier. Looking through a spotting scope, we identified it a the ghost bat (Diclidurus albus.) The book Mammals of Costa Rica, published by INBio, tells us that this insect feeder is so difficult to detect, that biologists have no way of knowing how common it might be. The ghost bat is one of the few bats that roost singly.
   Most bats look for dark places to roost. Some even make their own tents from the leaves of banana-like plants called Heliconias. If you see a leaf of this type doubled over, look underneath it. You may be surprised to find half a dozen winged fruit eaters sleeping there. Hollow trees are popular roosting sites. Many rainforest trees become hollow soon after reaching maturity. This may be an ecological strategy to attract bat colonies that will deposit large quantities of guano inside the base of the tree where it will serve as fertilizer. Caves are another typical roosting site. But when they choose to roost in peoples attics, bats often bring down the wrath of humans.
   Diane and I used to have an attic full of bats. This arrangement had its good points and bad points. The guano was welcome as a fertilizer for house plants, but the fine guano dust that filtered down into the house, was an unwelcome side-effect. We were continually disturbed by the scratching sound made by these furry little creatures when they come home to roost, however nobody complained about the mosquito control service they provided. So, we took measures to keep the guano dust down to a level we could live with, and we just got used to the scratching noises. Living with bats wasn’t so bad. Then one day we noticed that the bats had all disappeared. It took a while to figure out what had happened, but after some investigation we discovered that the bat extermination service was being provided by a common tree boa (Corallus ruschenbergerii,) that had taken up residence in our attic. The 2 meter long snake stayed out of sight and never came down into our living quarters. It also provided a rodent control service since its menu typically includes rats and mice. The downside of this is that we had to learn to do without the nitrogen rich guano fertilizer, and we had to put up with more mosquitos.
   We have occasionally had problems with bats eating fruit from our kitchen and then depositing fruit poop in other places in the house, like on my computer. The best way to control this is simply to cover the fruit. I definitely do not recommend poisoned bananas. The boa still lives in our old house, which is now occupied by students from Hacienda Barú’s volunteer program. The volunteers don’t know about the snake though, or they didn’t until they read this. In our present home, we have bats too. The roof construction here isn’t convenient for boas, so we have learned to live with the guano. It’s only a small nuisance and the bats pay their rent by eating mosquitos.
   If you still want to get rid of your bats, get on internet. There are lots of web sites that tell you how to build bat houses. If done correctly these are more attractive to the bats than your house. But please don’t kill them. Bats form an integral part of the fascinating web of life that surrounds us. If a snake moves in and clears them out for you, that’s fine. Boas only kill for food, and everything in nature has to eat. Sooner or later every living thing becomes food for some other living thing, even us.

Jack Ewings new book "Monkeys Are Made of Chocolate" has just been released.
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