Different call shapes

Bat calls consist of different components, known as:

FM – Frequency modulation

CF – Constant frequency

qCF – quasi –constant frequency.

Bat calls normally have 1 or 2 components. 

A CF is when the frequency remains the same over a period of time and is characterised by a flat horizontal line.

You also get a qCF component. This is when there is a slight change in the frequency over time, creating a call shape that has a shallow slope. Pipistrelle calls have a typical FM stroke with a short qCF tail.

A FM component is an almost vertical line that goes through a range of different frequencies over time. This is typically seen in most bat calls. 

Bat species: Myotis

Call shape: FM

Note: Long strokes through a wide range of frequencies.  

Bat species: Noctule/ Leisler’s

Call shape: Type 1: FM – qCF

                 Type 2: qCF

Note: Can be either types.  Type 1 is emitted in a cluttered environment, Type 2 in the open. 

Bat species: Serotine

Call shape: FM –qCF

Note: End frequency is below 32kHz

Bat species: Pipistrelles

Call shape: FM – qCF

Note: End frequency normally above 36kHz. Has a long FM/short qCF in a cluttered environment. Short FM/long qCF in the open. 

Bat species: Brown Long Eared

Call shape: FM

Note: Normally quite complex, FM sweep with a slight curve and has strong harmonics.

Bat species: Barbastelle

Call shape: FM

Note: Many different call types. Quiet calls.  Has short FM sweeps and start frequency is normally below 50kHz