Twilight zone: follow a scientist as she searches the skies to investigate one of nighttime's fliers--bats.

The sun is setting in the rain forest of French Guiana (gee-AH-nah), a country in northern South America. Nancy Simmons, a zoologist at the American Museum of Natural History (AMNH) in New York, hikes along a trail through the trees. She spreads out a large net and strings it between two poles like a volleyball net. She lodges the poles into the ground. Then, she waits.

As evening falls, some of the forest's night fliers--bats--emerge from their sleeping roosts. As they swoop past Simmons--THWAP!--a few of the bats collide with her net and get snarled in its threads. Simmons works through the night, carefully untangling the bats. She examines each one before setting it aside in a cotton bag. At the end of the night, she decides which bats to release and which to take to her camp for further study.

By setting up nets all around a small patch of rain forest, Simmons has captured 78 different species of bats. That's the highest number of bat species ever found in one place.

But French Guiana isn't the only region of the world teeming with bats. The animals are found on every continent except Antarctica. Bats account for nearly one fifth of all of Earth's species of mammals (see Nuts & Bolts, p. 11).

With so many bats flying in skies all over the world, scientists are trying to learn how each of the different species is related to the others. Follow along as Simmons shares her quest to construct a bat family tree.

What are some of the challenges of studying bats?

Bats are nocturnal (active at night). So when most people are going to bed, we are going to work. Besides having to stay up all night, it's difficult to study animals that fly in dark skies because you can't easily watch them. That's why we use nets to catch them.

Once you have captured a bat, what do you study?

I am a morphologist. That means that I study anatomy, or the body form of organisms. This ranges from what the bat looks like on the outside to what it looks like on the inside. For instance, I study color patterns on the bat's fur as well as the form of the bat's skull and the shape of its teeth.

What do these characteristics tell you?

You can learn a tremendous amount about how an animal lives by studying its anatomy. For instance, bats that eat insects need to puncture the insect's hard outer skeleton. So these bats tend to have sharp pointy teeth. A bat that eats fruit, on the other hand, needs to crush the fruit to squeeze out its juices. So fruit-eating bats tend to have broader, less pointy teeth--more like a human's.

Are there many kinds of bats?

There are more than 1,100 different bat species. There are large bats called flying foxes with wingspans of up to 1.8 meters (6 feet). These bats mainly eat fruit. Some city parks in Sydney, Australia, for example, are full of flying foxes.

The world's smallest bat is the bumblebee bat from Thailand. It is smaller than your little finger and its wingspan is just 8 centimeters (3 inches). These are insectivorous bats; they eat tiny flying insects. And there are all kinds of bats in between.

Has there always been so much diversity among bats?

The oldest records of bats are fossils (traces of ancient organisms) from the early Eocene period--about 52 million years ago. These fossils show that ancient bats were similar to the bats that we see today. And we have found the fossil remains of many different bat species, suggesting that bats were quite diverse at that time.

How are these different bat, s related?

That s one of the big mysteries that we are trying to solve. Most scientists now recognize 18 or 19 bat families. Bats are grouped into these families based on a variety of shared features, including anatomy and behavior. For instance, bats in one family may have similar teeth, skull form, and wing shape, as well as eat the same type of food. But scientists have not yet agreed on how these families are related. That's because there are so many features to match up, and the variation within and among different families is complicated.

Why is it so complicated?

Most of the features that we study seem to have developed independently in different bat species at different times. For example, millions of years ago, a group of insect-eating bats with pointy teeth may have started to eat fruit. As a result, over generations, the teeth of these bats would have become broader and less pointy.

At the same time, a group of unrelated bats also may have changed their diet from insects to fruit. These bats may have evolved broader teeth, too. So while these two groups of animals aren't closely related, they now share a similar tooth structure.

Sorting out these patterns of similarities is part of what makes it hard to distinguish the true relationships among bats.

How are you hoping to sort out the relationships?

We are gathering information on the traits (inherited features) of all of the world's bat species. In addition to studying anatomy and behavior, we are now using data from the bats' DNA, the molecule that carries hereditary information. We have found that each species shows slight differences in its DNA. Those variations give us additional data to find links between different bat species. By compiling this information, we hope to build a more complete bat family tree.

Why is it important to gather this information?

Learning more about bats will help us protect them. Many species of bats are endangered (in danger of dying out) because humans are destroying the habitats in which they live. By studying bats we can determine which bat species are at risk and find out how to help them survive.

Why it; it so important to protect bats?

Bats play a critical role in many environments. One of the important things bats do is they eat certain insects that are agricultural pests. For example, each night bats in parts of the U.S. eat thousands of tons of corn ear worms. These insects feed on food crops. If the big bat colonies in these parts of the country were wiped out, it could have devastating effects on our agriculture.

Nuts & bolts

Bats vertebrates, or animals with a backbone, and tetrapods, or four,legged animals. Bats are also mammals. They are warm-blooded, have skin covered in hair or fur, and their young feed on their mother's milk.

Bats are distinct from other mammals. They are the only mammals that can fly. Bats also have long life spans for species of their size. A small bat may live to about 30 years, while a similar-size mouse would live one year. And unlike many other small mammals, which give birth to large litters, bats usually have only one or two offspring at a time.

WEB EXTRA

To discover more about bats and their adaptations "Science Explorations" Web site. Be sure to take part in the live question and answer session with bat specialist Nancy Simmons. Visit: www.scholastic.com/bats

Check it Out:

Golden-capped fruit bats and many of their relatives can be seen in the American Museum of Natural History's Hall of Biodiversity. This permanent exhibition is devoted to a pressing environmental issue of our time: the need to protect and preserve our planet's biodiversity, or the variety and interdependence of Earth's life forms. The Museum has been researching and celebrating the natural world for more than 135 years and has more than 30 million objects in its extensive research collection. The Museum's 200 scientists travel around the world on 100 field expeditions each year, studying everything from leeches to woolly mammoths to the universe.

To learn more, ask your teacher, or visit www.amnh.org

DID YOU KNOW?

* Of the more than 1,100 species of living bats, only three species feed on blood. These bats use their sharp from teeth to make tiny nicks in a sleeping animal's exposed skin. Then they lick the oozing blood with their tongues. But these "vampire" bats do not harm the animals on which they feed.

* The little brown bat, or Myotis lucifugus, is one of the most common bats in the United States. It has a wingspan of approximately 25 centimeters (10 inches), and it can eat up to 1,200 tiny insects an hour. That's why the bats are so good at keeping insect pest populations under control.

CRITICAL THINKING:

* How is the adaptation of being able to fly advantageous for animals that eat insects and other animals? How might flight have helped bats to become so abundant around the world?

CROSS-CURRICULAR CONNECTIONS:

GEOGRAPHY: Do research on French Guiana. Then, create a travel pamphlet about the country. Be sure to include a map and a description of the country's climate and vegetation.

RESOURCES

* This Web site from Bat Conservation International has lots of information about bats. Includes activities for students and ideas and resources for teachers: www.batcon.org/home/default.asp

* Students can take a fun quiz and view bat slide shows at this site from the Organization for Bat Conservation: www.batconservation.org/content/Kidsandbats.html