What is the difference between soprano pipistrelle and common pipistrelle?

The soprano pipistrelle (Pipistrellus pygmaeus) and common pipistrelle (Pipistrellus pipistrellus) are two closely related bat species primarily distinguished by their echolocation calls and some morphological traits. The soprano pipistrelle emits higher frequency calls, typically around 55 kHz, while the common pipistrelle has lower frequency calls, around 45 kHz. Additionally, the soprano pipistrelle tends to be slightly smaller and has a more rounded wing shape compared to the common pipistrelle. Despite these differences, both species are often found in similar habitats and are challenging to differentiate without acoustic analysis.