Alien Earthlings

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Order: Chiroptera

Bats are some of the most diverse and misunderstood mammals on the planet today. They inspire fear and disgust and are often persecuted because of it.

People's fear of bats is probably derived of myths, concerns over the spread of disease and because they are simply so different than humans, as well as every other mammal.

White-throated Round-eared Bats - Lophostoma silvicolum

White-throated Round-eared Bats roosting in a termite mound - Lophostoma silvicolum

Until the 1960's scientists didn't know much about bats. It was not until they discovered bats could be captured  in Japanese Mist Nets that serious studies on them became possible.

Bats certainly are unique. They are the only mammals with the ability to fly. Among their ranks are the only mammals that subside chiefly on pollen and nectar and, of course, those that feed exclusively on blood.

When looking at the benefits provided by bats and comparing them with their negative aspects, one quickly realizes that bats play an essential role in maintaining a balance in our environment. Their benefits far outweigh any of their negatives.

Bats' ability to fly is one of their most amazing adaptations. Their hand has evolved into a wing covered with a stretchy, leathery, and very durable membrane. TTent-making Bat In Flight

he word Chiroptera, which is the name of their Order, literally translates into "handwing".

This is strikingly clear when viewing the photo on the left. The bats fingers are extremely large and run from wrist to the bottom of the wings while the thumb sticks straight up and is not covered by the leathery membrane that covers the other four fingers.

Another incredible adaptation is their ability to navigate by using echolocation. Echolocation works the way a sonar radar would. Bats emit high frequency sounds. The sound in turn bounces off their surrounding environment and returns to them. The sounds are emitted by way of the bats mouth and nose and may travel at approximately 340 meters per second! The bats then analyze the time it takes for the echoes to return to them and are able to tell how far away an object is. This gives the bats a perfect picture of their surroundings even on the darkest nights.

With about 1400 identified species, bats are the second most diverse mammal group, second only to rodents. They are found in every continent except Antarctica and make up about one quarter of all mammal species.

Pale Spear-nosed Bat - Phyllostomus discolor

Pale Spear-nosed Bat - Phyllostomus discolor

Nearly half of the mammals in Costa Rica are bats. We have 117 confirmed species in Costa Rica, about eight percent of the world's known bat species. Out of the 117 bat species present in Costa Rica, 80 have been collected on the Osa Peninsula. This number is quite remarkable when you think about it. The United States, which has 150 times the landmass of Costa Rica, only has 47 bat species and the entire continent of Australia only has 70 recorded species.

In Costa Rica, there is great diversity among bats. They differ in where they hunt, how they breed and what they eat. They range in size from the tiny Black Myotis (Myotis nigricans), which has a wingspan of about 5 centimeters and weighs about 5 grams, to the False Vampire (Vampyrum spectrum), which can have over 80 centimeters in wingspan and weigh about 200 grams. The False Vampire feeds mainly on sleeping birds and can take Motmots, Pigeons and Parrots weighing about as much as the bat does!

Thomas' Fruit-eating Bats - Dermanura watsoniA large variety of bat species means a high degree of specialization among them. Individual species usually stick to certain height levels of the forest when they forage. Some may forage over the water or way above the forest canopy. The height and location in which they forage is dictated by their very specialized diet. In Costa Rica about 53 percent of bat species feed on insects, 25 percent feed primarily on fruit, 10 percent eat mostly nectar and pollen, about 7 percent feed on other vertebrates or their blood, and at least 5 percent are omnivores.

What they eat will in turn dictate when and how they breed. Female bats give birth while roosting and the pups are usually born tail first. After their feet emerge, they will clamp onto the mother's fur and help pull themselves out. Newborn pups may weigh as much as 40 percent  of their mother's body weight! Note the baby being nestled underneath the Brazilian Long-nosed Bat (Rhynchonycteris naso) female at the bottom of the row of bats pictured on the right.

Research seems to indicate that bats time their reproductive cycles so that their offspring is weaned at a time of year when food is most abundant.

Insectivores usually have only one litter per year and it is normally at the end of the dry season. This way the pups will be weaned by early rainy season when a large amount of  insects are available to feed on.

One of our smallest bats, the Black Myotis (Myotis nigricans), breaks this pattern. It is unique in that females may have up to three litters per year. These bats are insect eaters, but they manage to produce litters continuously throughout the year with a short pause at the end of rainy season.

Because in the tropics flowers and fruit are available most of the year, bats that feed on fruit and nectar usually have a litter at the end of dry season and another litter late in the rainy season.

Commissaris's Long-tongued Bat - Glossophaga commissarisi

Commissaris's Long-tongued Bat - Glossophaga commissarisi

Finally, the Common Vampire (Desmodus rotundus) will breed throughout the year, with individual females producing about two litters per year. These bats enjoy a stable food source and are unaffected by the changing of the seasons.

Bats generally have cryptic coloration and their fur is usually adorned with different shades of black or brown. Greater Bulldog Fishing Bats (Noctilio leporinus) have beautifully colored orange fur. We also have two species with white fur, which is unusual among bats. The Northern Ghost Bat (Diclidurus albus), which is found on the Osa Peninsula, and the Honduran Tent-making Bat (Ectophylla alba) which is only found on the Caribbean Slope. These tiny bats are about the size of a wine cork and with their fuzzy white fur and yellow ears and nose are probably the most beautiful bats in the country.

Honduran Tent-making Bats - Ectophylla alba

Honduran Tent-making Bats - Ectophylla alba

 

Another amazing bat group are Disk-winged Bats (Thyropteridae). These bats are unique in that they are the only bats in America that roost right side up. They have suction cups on their thumbs and on their heels which allow them to stick to smooth surfaces. We have found them sticking to the smooth tile on our bathroom wall!

 Spix's Disk-winged Bats - Thyroptera tricolor

Spix's Disk-winged Bats - Thyroptera tricolor

There are two species of Disk-winged Bats in Costa Rica, both are aerial insectivores and both species are found in Drake Bay. Spix's Disk-winged Bats roost inside new, rolled up, heliconia leaves in the process of unfurling. After the leaf has opened too wide for the bats' taste, they move on to another leaf.

Peters' Disk-winged Bats are rare to see, but we have also found them in Drake Bay. These tiny bats live in small colonies and usually roost inside cones which form on dead banana leaves. We found and photographed the colony of Peters' Disk-winged Bats shown below in Drake Bay.

 Peters' Disk-winged Bats - Thyroptera discifera

Peters' Disk-winged Bats - Thyroptera discifera

The Fringe-lipped Bat (Trachops cirrhosus) is another incredible bat that is well worth mentioning. This bat also feeds on insects, but is a specialist on frogs. It locates calling male frogs, not by echolocation, but by using its sense of hearing. Studies have shown that the bat can distinguish between toxic frogs and edible ones based solely on their call. Researchers have carried out experiments where they play the calls of toxic frogs that don't live in the area and the bat still knows to avoid them! If they play calls of edible frogs, the bat will violently attack the speakers! Scientists think the bats can distinguish between the two based on the frequency of the frog's call.

Fringe-lipped Bat - Trachops cirrhosus

Fringe-lipped Bat - Trachops cirrhosus

After learning a little bit about these exceptional animals, it is easy to quickly develop a passion for bats. Their diversity in shape, biology, and abilities are nothing short of extraordinary. Not only are they fascinating, but they are incredibly beneficial to humans and the environment.

Insect eating bats play a crucial role in controlling insect populations. Insectivore bats consume a huge numbers of insects that could potentially cost farmers and foresters billions of dollars and spread disease among humans. It is estimated that just the 20 million Brazilian Free-tailed Bats that inhabit Bracken Cave, in Texas, devour some 225 metric tons of insects every night!! On average a family car weighs about 1.5 metric tons, meaning that this bat colony alone consumes approximately the weight of 150 family cars in insects per night, a truly a staggering feat!

Northern Big-eared Bat - Micronycteris tresamici

Northern Big-eared Bat roosting in a hollow tree - Micronycteris tresamici

Little Brown Bats often eat mosquitoes and can catch up to 1,200 small insects per hour. A typical Big Brown Bat colony can consume enough Cucumber Beetles to avoid tens of millions of the beetle's larvae depleting a farmer's crop.  Imagine a world without bats. The guano produced by these insectivore bats is also a valuable fertilizer.

Northern Ghost Bat - Diclidurus albus

Female Northern Ghost Bat with her pup - Diclidurus albus

It is estimated that bats are responsible for the pollination and seed dispersal of hundreds, possibly thousands, of trees and plants. Plants and trees like Ficus, Cecropia, Solanum, and Piper depend on bats for seed dispersal. Scientists estimate that Balsa Trees (Ochroma pyramidale) rely solely on nectar and pollen eating bats for pollination.

Fruit eating bats play a key role in regenerating forests. Unlike birds, who normally defecate while perching, bats tend to defecate in flight. This means that seeds will fall to the ground and develop far from the shade of the parent tree, perhaps in an open field.

Mesoamerican Tent-making Bats - Uroderma convexum

Mesoamerican Tent-making Bats - Uroderma convexum

Unfortunately, bat populations are declining worldwide. The causes are the usual suspects: global warming, destruction of habitat, human persecution, pollution and the use of pesticides. Pesticides are especially harmful. They are used on the insects that are consumed by bats, and end up poisoning the bats. This has led to serious declines in some areas.

Another budding danger to bats is the growing number of wind turbines being erected to harvest electricity. Greater Bulldog Bat - Noctilio leporinus

It seems that bats, unlike the birds that hit them by accident, may be attracted to the turbines. One study in West Virginia in a site with 44 turbines documented between 1,300 and 2000 bats killed during a six week period.

But perhaps the most troubling development for bats in the last few years is White-nose Syndrome. This mysterious disease has killed tens, perhaps hundreds of thousands of bats in North America. Up to 95 percent of the population of infected bat colonies are being wiped out throughout hibernation caves in New York, Vermont, Massachusetts, Connecticut, and possibly Pennsylvania. They call it White-nose Syndrome because infected bats exhibit a white fungus on their noses.

The scariest thing is that scientists have no idea what is causing this bat epidemic or how to stop it. Infected bats are leaving their hibernation caves earlier than normal in a severe state of emaciation and dehydration. Many also have wing injuries, apparently acquired during their hibernation, and the bulk of the bats belonging to infected colonies are usually discovered lying dead on the cave floors.

We encourage all of our readers to visit the Bat Conservation International Website at http://www.batcon.org/home/default.asp and find out what you can do to help save these remarkable animals. It is time we realized how important bats really are to our planet and take the necessary steps to protect these wonderful creatures. Wrinkle-faced Bat - Centurio senex

The following pages are dedicated to four of the most commonly seen bats on the Osa Peninsula: Tent-making Bats, Greater Bulldog Fishing Bats, White-lined Bats, and Brazilian Long-nosed Bats. All bats appearing on these web pages are live specimens photographed in the wild. The photograph of the Pale Spear-nosed Bat at the top of the page was mist-netted at Sylvan Falls and was being handled by Fiona Reid.

References:

Bat Conservation International Website Articles

Available at: http://www.batcon.org/home/default.asp

Beletsky, L.  2005  Travellers' Wildlife Guides Costa Rica  Interlink Publishing

Janzen, D.  1983  Costa Rican Natural History  University of Chicago Press

LaVal, R. & Rodriguez, B.  2002  Murcielagos de Costa Rica/Bats  Editorial INBio

Wainwright, M.  2002  The Natural History of Costa Rican Mammals  Zona Tropical

Wilson, D.  1997  Bats in Question  Smithsonian Institution Press

 


Mammals of the Osa Peninsula

Mammal Files

Mammals Home Page

Bats Home Page

Brazilian Long-nosed Bats

Greater Bulldog Fishing Bats

Tent-making Bats

White-lined Bats

Brown-throated Three-toed Sloth

Kinkajous - Potos flavus

Common Opossums - Didelphis marsupialis

Northern Tamandua - Tamandua mexicana

Central American Woolly Opossum - Caluromys derbianus

 

 

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