Echoes in the Night
What do bats do in the dark. Following the Frontiers special Expedition Panama: Rat Soup, One of the world's leading authorities on bats -- biologist Elisabeth Kalko of the Smithsonian Natural History Museum -- answered viewers' questions about these fascinating nocturnal creatures in an Ask the Scientists panel. Here are viewers' questions and her answers:
What kind of signals do vampire bats make? You talked about fruit bats and insect eating bats, but what about meat eating?
Vampire bats belong to the large family of New World leaf-nosed bats (Phyllostomidae) which only occur in the tropics and subtropics of the Americas. In this family one finds fruit-eating bats, nectar-drinking bats, meat-eating bats, bats that take large insects from the vegetation (gleaning bats) and also the group of vampire bats (including three species; only one of them, the Common Vampire, has become abundant in places with large numbers of cattle). Interestingly, ALL of the New World leaf-nosed bats produce very similar echolocation calls which are difficult to distinguish among most species. The calls are short and sweep rapidly through a broad range of frequencies, they are thus termed Frequency-Modulated calls. These calls are very well suited to give information to the bat about its distance to obstacles. The bats use echolocation mostly to find their way in the darkness among the vegetation. To find their food, they rely largely on smell (in case of fruit-eating and nectar-drinking bats), or on sounds produced by the prey itself (such as mating calls of katydids or frogs), to a limited degree they also use sight, and, in case of vampire bats, they even use heat as a cue to find their food! Vampire bats have heat sensors that tell them when a desired victim such as a cow is close by.
Is it fun working with bats? Have the bats ever bitten you?
Yes, it is A LOT of fun working with bats! This group of animals is so diverse and fascinating in its life habits and there are so many unknown aspects of their lives still waiting to be discovered. Every time I go into the field or work with trained bats in a flight tent I am learning something new. And, yes, I also have been bitten by bats, although very rarely. Their teeth are truly sharp and needle-like. But bats only bite in defense and would never attack. We handle bats very carefully not to harm them and also not to be bitten.
How did you become interested in bats, when very few people ever see these night time creatures?
I was always very interested in animals and plants, actually, my favorite animals when I was a kid were toads, frogs, and birds! When I was in school I joined a group of people interested in nature conservation and protection and had a chance to get to know something about bats. But at that time this was very little since not much was known about them. When I came to the university to study biology I was fortunate to get into contact with a group of people led by Dr. Schnitzler (Department of Animal Physiology, University of Tuebingen, Germany) working with trained bats in the lab. They were looking for somebody who would be interested to work with bats in the field. This was a wonderful opportunity for me to combine my interest in field biology with other aspects of science. And with a lot of novel equipment (multiflash photography, night vision scope, bat detector), most of it developed and modified at the institute in Tuebingen, it was suddenly possible to learn a lot more of the lives of these creatures which are usually so difficult to study. I was really fascinated and found (until today...) that the combination of technology and detailed field studies on natural history, behavior, and ecology is a very powerful tool, particularly for bats! Luckily, after I finished my thesis, I then had the opportunity to get from the temperate zone to the tropics, where such a high diversity exists.
The photographs of the bats that appeared on last week's show were incredible! Are your photographs of bats available for viewing on-line and can they be purchased?
Sorry, my photographs are (not yet) available for viewing on-line or for purchase. Maybe in a combination of science and some artwork they would be an interesting object for sale? And the money could then be used for more bat research!
Your research on the show was really neat! One thing it did not explain was what that instrument is that you take out with you that makes the bats' calls slow down so we can hear them. I have always heard that bat's calls are too high-pitched for the human ear to hear. What do you call that machine? Did you invent it? How does it work?
Yes, most bat calls (with only a few exceptions) are so high-pitched that we (humans) cannot hear them. The equipment that we are using to make the bat calls audible is called "bat detector". I did not invent it but the machines we are working with have been modified at our lab at the university of Tuebingen in Germany for our special purposes. Some types of bat detectors are also commercially available. This is how the machines work: The high-pitched calls of the bats are picked up with a special microphone that is sensitive in the high frequencies. They are amplified and then fed into the actual "heart" of the machine. There, at least two things are done with the incoming signals: first, to make the calls audible to the human listeners, the incoming signal is either divided by ten and thus transformed into a lower frequency range suitable for humans or it is mixed with an internal frequency which can be chosen and the difference between the incoming frequency and the internal frequency is audible for humans (heterodyning system). Second, for further analysis (resulting for instance in the colour pictures of calls (sonograms) that you saw on the screen in the show) the high- pitched signals are recorded without previous transformation either in real-time on a special, high-speed tape recorder or they are slowed down (in our case 15 times) and recorded on a standard Walkman. Slowing down means that a call which is originally for instance at a very high pitch (lets say 150 kilohertz) and cannot be heard by us will be at a slow-down rate of 15 at a frequency of 10 kilohertz which is well within our hearing range. What you heard in the show are two things: first, the rapid, staccato-like calls of the bats in real-time (heterodyning) and the slowed down calls of the bats for the recordings. I hope this is not too complicated!
How did you learn to recognize the difference between all of those different species of bats and their different calls?
Learning to associate the different calls of bats with the different species of bats is often a difficult task that requires a lot of field work and patience. It's best to find a group of bats in a roost, for instance, where the species can be identified and then make recordings when identified bats fly around the roost. Another option is to record bats coming to water holes for drinking and catching them with mistnets for species identification. A third option is to catch bats with mistnets, identify them and release them while making recordings. In some cases, flight style, size of bat and other characteristics are so typical that the species can be recognized easily in flight. However, the tricky part is that bats often change their echolocation behavior depending on whether they fly high above the ground in open, unobstructed spaces or close or within the vegetation. Hence, bats that are hand-released may produce calls that are very different from the calls that they make when they fly high above the trees. However, with time, patience, and lots of field work we have now gathered results on more than 50 bat species (aerial insectivores, that is bats that catch insects in the air as opposed to the large group of bats living mostly in forests and gleaning food from surfaces such as large insects, fruits etc.) for parts of South and Central America alone. It is somewhat similar although not exactly the same like identifying birds by their songs. Since aerial insectivorous bats are usually difficult to catch in mistnets but in many cases rather easily identified by their calls, this method of acoustic monitoring means a large step forward in our understanding where certain bats live, what kind of habitats they need, how they interact with other organisms, and what we can do to preserve and protect them.
We took the quiz about bats in the teaching guide for Expedition Panama. We learned that bat guano is used to make some antibiotics. Do you know what kinds of medicines are made from bat guano? from Mr. Shrout's period 3.
Sorry, although I tried to find more information I could not find any more details on this topic. It seems that there is no published research so far that substantiates this statement. Maybe in the future we will know more about that! However, bat guano can surely be used as a very good fertilizer for the garden. And here some important things to consider when dealing with bat guano: always be very careful not to inhale dust that is created when shoveling dry guano accumulated under a bat colony on the attic into a bag. Bat guano may contain spores of a fungus that can lead to a serious lung infection (histoplasmosis). Best is to protect the hands with rubber gloves and to wear a mask.
Forum Moderator adds: Here is additional information on this topic from Bat Conservation International's Site (www.batcon.org):
Bat droppings in caves support whole ecosystems of unique organisms, including bacteria useful in detoxifying wastes, improving detergents, and producing gasohol and antibiotics.
An anticoagulant from vampire bat saliva may soon be used to treat human heart patients. Contrary to popular misconception, bats are not blind, do not become entangled in human hair, and seldom transmit disease to other animals or humans.
Why do you think there are many more types of bat species in the tropics than in other places in the world?
It is truly astonishing to learn about the large numbers of species of bats and other organisms in the tropics. There are a wide variety of explanations for this richness. For instance, in the temperate zone with strong winters you'll find only bats that eat insects during the summer and have the ability to hibernate. However, in the tropics you'll find insect-eating bats as well as many species of bats that eat fruit, nectar and pollen. This is possible because in the tropics fruit and flowers are produced all year-round, not interrupted by harsh winters. Further, a much greater number of plants and insects are found in the tropics, which in turn allows many more bat species to live together.
I am doing a report on bats and I am having a little trouble narrowing my subject. In your personal opinion, what is the most interesting type of bat? Do you have suggestions about good places to look for information about bats? (email@example.com)
That is truly a very hard question, because each bat has a fascinating life story of its own! Surely there are some bats that are better studied than others and thus we know more about them. I suggest you first get an overview about bats in a popular book and then decide which one you find most interesting! For me, every bat, even vampire bats which have such a bad reputation because of their blood-drinking habits, is a fascinating creature.
To help with the search for the most interesting bat, I have listed a number of books which will give a good overview about bats and their life histories. This list is by no means complete. All of the books that I am listing have very good colour photographs and/or illustrations to give an idea about the diversity in bats. I have included approximate prices, please check, since they may have changed
Bats of the World: a Golden Guide (1996) by Gary Graham, 160 pp (about $6)
Bats: facts on file (1992) by M. Brock Fenton, 224 pp (about $45)
Bats in question (1997) by Don E. Wilson, 192 pp (about $49)
The world of bats (1993) by K. Richardz and A. Limbrunner, 192 pp (about $35)
America's Neighborhood bats (1988) by M. Tuttle, 96 pp (about $19.50)
What did you do to become such a good bat specialist? How can I become a bat scientist? I am now in the seventh grade.
I became a bat specialist by reading a lot about bats and by going out a lot and trying to see and learn as much as possible from bats in the field. It was, for instance, a great joy for me to discover after long observations at dusk that I could, after some time, discriminate little bats fluttering by on their way to their hunting ground from birds darting by like swifts and swallows! Good places to watch bats are places around street lights, near forests and/or gardens or over water at lakes and rivers in nights with high insect activity. Also, when you know houses where squeaking and rustling noises are reported from the attic, watch the house when night falls to try to see whether bats fly out there.
It also helped me a lot to join local conservation groups and get better ideas where bats roost and forage. To become a bat specialist I recommend reading about their lives in good textbooks (I gave a selection of those in a previous answers) and to contact local bat groups to join them in their work. There are quite a number of people around, mostly in conservation-oriented groups, who observe and protect bats. In some places, even guided bat tours with detectors listening to bat echolocation calls are available. Contacting Bat Conservation International in Austin, Texas, is also a great way to get many interesting tips and news about bats, educational programs and suggestions how to observe and help them (www.batcon.org). It is important, however, when you have a chance to get close to bats to be always careful, let specialists handle them and remember that bats (although seldomly) can carry rabies. Although they will do it only in defense and never attack, bats do bite when they feel restrained.
Has your work with acoustical monitoring helped to understand how bats seem to be able to simultaneously keep track of prey, obstacles, fellow bats darting about(maybe even diving after the same target), and other important variables?
Yes, our work on echolocation of bats has helped us a lot to answer many questions. We have learned how bats adjust the type of their signals to different habitats and different kinds of food they take. For instance, a bat that flies in open spaces way above the trees or the ground emits echolocation calls that are well suited to detect prey (insects) over long distances. In contrast, bat echolocation calls that enable them to distinguish potential food from the surrounding vegetation and to avoid obstacles.
We have also learned that some bats do not only use echolocation but also other senses to find their food. Fruit-eating bats, for instance, have a keen sense of smell and thus can find ripe fruit in the forest fairly easily. Bats that fly in obstacle-rich surroundings use echolocation to find out where and what kind of obstacles there are and skillfully maneuver around them. It appears that each bat has a precise idea about the timing and other characteristics like frequency structure of its echolocation signal and expects the echoes back in a certain time window. Thus, it can discriminate echoes from its own calls from that of fellow bats hunting in the same area. Sometimes, of course, even the best system fails and bats may almost "crash" into each other when they pursue the same target or one finds bats with large holes in their wings where they have inadvertently touched spines and thorns. But these "accidents" are rare. The exciting part of our research on echolocation in bats is that the more we know about it the more interesting questions and links are opening up. So, this will be a field that will continue to keep us and many others busy for a long time...
What is the largest bat and the smallest bat?
The smallest bat in the world is the tiny bumblebee bat. It lives in Thailand and feeds on minute insects. Its body measures only about 30 mm and it weighs as little as 2 g! The largest bat is a giant flying fox that may weigh around 1 kg and has a wingspan of 1.50-1.50 m!
How fast does the fastest bat fly?
So far, we do not know precisely how fast the fastest bats fly. However, free-tailed bats that hunt for insects way up in the open sky surely reach 30-50 km/hour and presumably even more when they "race" from one side of the horizon to the next. They feed mostly on large insects like huge beetles which are sparsely distributed in space. Thus, they have to fly long distances to get enough food per night.
Why do bats sleep upside down?
Why bats hang upside down is a really interesting question. Let me try to answer it. I think that it is largely to the construction of a bat's body, particularly the way how the wings are formed and attached to a bat's body. The thin membrane of a bat's wing stretches from its elongated fingers to the legs and attaches to the sides of its body. Further, in most bats, a large membrane connects both legs and is used by the bats to capture insects in the air like a pouch. Thus, the legs of a bat are not free but are "engulfed" by wing and tail membrane. Consequently, bats did not have the "freedom" like birds to develop many different kinds of legs like the long legs in storks or short legs in ducks. It appears that for a bat the easiest way to stow away the membrane is to hang upside down. Whether this is the main reason for it or not, I do not know. But looking at bats hanging from branches and ceilings it seems to be a rather logical explanation to me.
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