"Lo, though nature red in tooth and claw..."

-Alfred Lord Tennyson, 1850

All About Bats

Posted by MaryEllen On 8:05 PM

Bats are fascinating, and beautiful, animals. Even leaving aside the total coolness of flying, they also have some amazing hardware. A bat, using echolocation, can detect something as fine as a human hair from 50 feet away. And all those stories about bats getting caught in people's hair - either not true or an isolated horrible accident. Bats that eat insects fall roughly into two groups - gleaners and flyers. Gleaners take insects that have settled on something else - for instance, they will swoop close to a heat source (like one's head) because the heat source will have attracted insects that are likely sitting or hovering near your head. They also swoop by flowers, and many desert flowers stay open at night for this specific reason - they attract insects, which attract bats. The bats, the gleaners, stick their heads into the flowers to get the insects. The pollen in the flowers comes off on the bat's head, and the bat carries it to the next flower, thereby pollinating the plants.

The other type of insect-eater, flyers, they eat insects on the wing - they are the ones you see swooping, apparently randomly, at night. They are hunting insects, swooping after them and catching and eating them mid-flight. Bats have very high metabolisms and need to consume pounds of insects each night, which they do. Bats are a much more effective form of insect control than anything man-made.

In the rain forests in South America, many trees and plants have fruits that specifically attract bats - guava and bananas are examples. The fruit-eating bats (which do not use echo-location) are attracted to these kinds of fruits and will eat them off the trees, then as the bats fly around, the seeds from the fruit will process through the bats and be spread around the forest. It is estimated that bats provide about 80% of the pollinating and reforesting in the rain forests. They are many kinds of tree and fruit seeds that will not germinate unless they have passed through the digestive system of a bat first.

Vampire bats, the most feared of this generally harmless species, have an astonishingly complex social system, one that pretty much has scientists stumped for an explanation. Female bats (who congregate in what are called "maternity roosts", all of the mothers and babies together) appear to be totally altruistic - that is, they will share their food if another bat is ill and hasn't gotten anything to eat, and they will also nurse babies that are not their own. Most scientists feel that social systems in animals operate on a pretty strict system of either hierarchy (I give you food because you rank above me and I am currying favor, or I give you food because you rank below me and I want you to do something for me) or reciprocity (I give you food with the expectation that you will give me food later). But bat colonies are huge and there seems to be no correlation between bats giving food and receiving it - a bat will give food to another bat and never get food from that bat, ever. A bat will nurse a baby that is clearly not her own, and never have her young nursed by any other bat. So it seems that bat society either functions on a reciprocal system so complex that we humans can't grasp it, or bat society is in fact truly altruistic. If so, it would be pretty much the only model of such behavior in the animal world.

If only humans were so caring. The bat population in the US is way down, due a couple of things. One of them is simply people going into caves. When bats hibernate, they store up just enough energy to get through the winter and to get themselves woken up in spring. But when cavers come through the caves and disturb them, they wake up. Then they go back to sleep, but they no longer have enough energy to last, so they don't wake up again - they die of starvation in their sleep. And since the cave explorers don't really see the effects, they have no idea what they have done, and continue tromping through the caves and disturbing bat populations. Then after a few years they say "You know, there used to be a ton of bats here, I don't know where they have all gone..."

The other threat to bats is the lack of protection for species that migrate. Mexican Free-tails, which migrate to Mexico in the winter, are often killed by local people who fear them, and also they ingest toxic doses of DDT and other pesticides from the insects that they eat. Then, during their migration, as they are flying over the Pacific, they drop out of the sky, dead from DDT. Again, since people don't see masses of them dying, they don't really know. It's only recently that we humans have begun to understand the threats facing bats, and to take positive action to protect them.

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