Ultra-soundscapes revealed

 Spring is the breeding season for birds but our native bats are just starting their courtship behaviour. Furthermore, as the days get shorter, bats become active earlier, at a more convenient hour.

Listen here to a territorial male Noctule recorded via my heterodyne detector.


Full-spectrum recording

Now, conventional detectors have their uses but they also have limitations and I now favour unadulterated full-spectrum recordings rather than using derived signals.

You need a 192 kHz sampling rate and a spectrogram facility so practising recordists using a modern CF-card recorder and PC editing software have the basic equipment to get started. Then you need a microphone with an extended frequency response such as the trendy WM61 capsule, which is a lot cheaper than a bat detector.

I am enthusiastic about the capabilities of my kit that has taken my understanding of the Chiroptera to a new level. It really is a quantum advance for survey work and that is not hyperbole!

I am having to teach myself heuristically but I am making headway. I am finding new local records all the time and it turns out that some so-called rarities are more elusive than really rare.

For example, I have been trying to locate Serotine feeding sites for years and in August, I finally tracked them down making several recordings that translated into presentable sonograms, although they do not reproduce well here.

Ecolocation pulses

Serotine ecolocation pulses

Wing clapping during courtship has been reported, so there is a target for an ambitious sound recordist!

Dynamic range
Dynamic range is an issue for the sound pressures can be very high at short range and I frequently over-record the ‘loud’ species.

In contrast, when recording at high gain, I often capture the elusive Brown Long-eared Bat (Plecotus auritus). This is common enough and is variously known as the ‘gleaning’ or ‘whispering’ bat. The literature states that its radar is too ‘quiet’ to register but over the summer, I have logged quite a few contacts.

I would encourage mainstream wildlife recordists to cast their net more widely and target the ultrasonic world.  It is a rewarding genre and new discoveries await.


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