Interpreting Detector Sounds
There are 4 main elements to listen for when using heterodyne detectors to help you to tell the species apart:
• Repetition rate
The repetition rate refers to how fast each bat call follows the previous one in a series. In general it is related to the size of the bat (big bats tend to be slower) and the habitat (out in the open bats make slower calls than when flying between obstacles among trees, hedgerows etc).
Rhythms relate to how the bat is flying. Bats flying in straight lines have regular rhythms and bats that tend to make lots of twists and turns tend to have erratic rhythms.
The tonal quality or flavour of the call varies between species. Some use deep, rich sounds and others flatter, ‘tinny’ calls. It relates to the duration of the call and long calls sound richer than short ones. The pitch or note helps us to find the peak frequency or where the bat is putting more energy into the call.
Different bat species will show different call characteristics based upon the type of flight they use, their wing and body shape, where they feed and how they feed.
Some may make fairly slow and rich sounding calls in an erratic pattern and others make fast and dry sounding calls in a regular pattern.
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