Bat Anatomy
With so many species in the forest, it’s not always easy to identify bats, especially as we might catch 10-15 species in a single night. We use field guides and identification keys to tell them apart — these help us sort the bats by certain characteristics such as body size, size and shape of the ears, wings, legs, teeth, noses or tails.
To get started, it helps to know what the different parts of the bats are called. Let’s start with the fingers, wing and tail. Have a look at the photo below and try and find
- the five fingers -these are called digits, and notice that the thumb is the first digit
- the forearm
- the leg
- the hindfoot
- the tail
- the interfemoral or tail membrane
The tail and tail membrane often differ in length and can be very helpful in telling families of bats apart.
Tails
One of the first things too look at then is the tail. Does the bat even have a tail? Some species don’t, or it’s so small we can’t see it!
Tail tip of Nycteris tragata with Y-shaped cartilage
If it does have a tail, how does the tail relate to the tail membrane? In the photo above, see how the tail goes all the way to the end of the tail membrane. This is typical for the family Vespertilionidae. In other families, the tail may actually stick out beyond the tail membrane. In Nycteris tragata and all the bats in the family Nycteridae, the tail ends in a strange piece of cartilage that is in the shape of a Y or T!
Ears
Ears also vary among families. First of all they can differ in their size and shape. Look at the picture below to see just how many kinds of ears there are!
Look left to see how many different shapes and sizes of ears can be found. Look right to see the different tragus shapes for just five species
Then there is the tragus. This is a small piece of cartilage and flesh that sticks up near the entrance of the ear. Its actually part of the margin of the ear — we have a small tragus too! It is believed to help echolocating bats estimate the heights of objects, but not all species have a tragus, and again they come in lots of different shapes and sizes, as you can see from the picture on the right.
In some families there is an antitragus instead of a tragus. The antitragus is also part of the margin of the ear, and is opposite the tragus in humans.
Noses
Well, of course all bats have a nose! But in some species the nose is relatively simple, whereas others, like the Murina have tubular nostrils. Species in the family Rhinolophidae and Hipposideridae have complicated noseleaves, and the Nycteridae also have flaps of skin around the nose as well.
Three examples of different noses! Rhinolophus (left) and Hipposideros (centre) species have a noseleaf, and Murina (right) species have tubular nostrils
Fur color
Fur color can be helpful in telling species apart, especially if there are bands of color or if the tips of the fur are different from the base of the fur.
Bands of fur color, as in the Phoniscus, on the left can be helpful for identifying species, as can the golden-brown fur tips seen in Kerivoula krauensis on the left
But sometimes bats of the same species might be slightly different colors, just because they may be different ages, or because of bleaching in the cave. So, we have to be pretty careful when using color for identification!
These two individuals have rather different fur color, but they are both Hipposideros bicolor 142 kHz!
Body Measurements
With a bit of practice it’s not too hard to work out which genus a species belongs to, but often to be sure of the actual species can be a bit tricky. We may have to look at tiny details of the noseleaf structure, or try and look at the teeth, which isn’t easy in small bats!
Details of noseleaf structure can help tell similar species apart, but it's not always easy!
Often though we may be able to tell two species apart based on measures of their size, and the two most useful measurements are the length of the forearm (in mm) and the weight of the bat (in grams).
To weigh the bats we wrap them inside a piece of ladies' stocking (left) and use a spring balance to get the body mass in grams. We use dial calipers to measure the forearm length (right)
