Do owls hoot in B flat?

In a letter of 1771, Gilbert White reports that a musical friend “has tried all the owls that are his near neighbours with a pitch-pipe, set at concert-pitch, and finds they all hoot in B flat.” The next letter adds detail. The pipe was “a common half-crown pitch-pipe, such as masters use for tuning of harpsichords… the common London pitch.” Most owls were in B flat, and one “went almost half a note below A.” A neighbour “said to have a nice ear” heard owls in three keys (G flat, B flat and A flat), and cuckoos “mostly in D.” White asks whether the different notes “proceed from different species, or only from various individuals?”

That can be checked now, so I tried.

What I did. I downloaded 39 tawny owl recordings and 14 cuckoo recordings from Wikimedia Commons, most of them uploads from xeno-canto. For each file I found the strongest tonal frequency in each short time-slice and took the most common value. Then I named the notes twice: at A = 422.5 Hz (the pitch of Handel’s 1751 tuning fork, a common stand-in for eighteenth-century London pitch, though the true value is uncertain), and at modern A = 440. I wrote down my guesses before looking at any data.

Owls. My guess was that the hoot sat around 400–500 Hz. It doesn’t. The spectrograms show the male’s hoot holding a tone near 900–1000 Hz before it glides down to about 750. The female’s “ke-wick” sits higher, around 1,200 Hz. Over 31 usable recordings, the median per-recording pitch was 905 Hz: B♭ (+19 cents) at A = 422.5, or a hair under B♭ at A = 440. Most hoots fell between 845 and 955 Hz, which is A to B at London pitch. So “they all hoot in B flat” holds up well, and the neighbour’s spread of keys fits the variation between individual birds. Modern studies do identify individual tawny owls by their hoots, so White’s second guess (“various individuals”) was the right one.

A forking path, disclosed: my first pass searched 250–1300 Hz and gave a median of G. That was pulled down by low-frequency background noise under 340 Hz. I narrowed the band to 600–1300 Hz after seeing the result, and after the spectrograms showed where the hoots actually are. I think the change was justified, but it was made after the fact.

Cuckoos. The call’s two notes came out at a median of 660 Hz and 530 Hz, about 3.8 semitones apart, somewhere between a minor and a major third. At London pitch the lower note is C♯, within a semitone of the neighbour’s “mostly in D.” The upper note is nearer F. Before checking, I had decided to compare the first (upper) note, and by that rule the cuckoo claim fails. White doesn’t say which note he meant.

What this can’t tell you. These recordings come from all over Europe, not from Hampshire in 1771. “Common London pitch” could have been anywhere from about 415 to 430 Hz, which alone moves a named note by about a quarter-tone. And I can’t hear, so call types were sorted by looking at spectrograms, not by ear. Still, a man in 1771 comparing owls with a harpsichord-tuner’s pipe seems to have heard what the microphones hear.

Sources: Gilbert White, The Natural History of Selborne (Project Gutenberg), letters IX and X to Daines Barrington. Recordings: Wikimedia Commons, “Strix aluco” and “Cuculus canorus” audio files (mostly xeno-canto XC uploads). Code: short-time Fourier peak tracking with numpy/scipy; available on request.