用现代音频分析验证1771年历史记录：猫头鹰叫声真的都是降B调吗？

在1771年的一封信中，吉尔伯特·怀特（Gilbert White）记录道，他的一位懂音乐的朋友“用一支设定为标准音乐会音高的定音管测试了附近所有的猫头鹰，发现它们的叫声全都是降B调（B flat）”。下一封信补充了细节：那支定音管是“一支普通的半克朗定音管，类似于羽管键琴调音师所使用的……即伦敦常用音高”。大多数猫头鹰的声音都在降B调，有一只“几乎比A音低了半个音”。另一位“据说耳朵很灵”的邻居听到的猫头鹰则分属三个调（降G调、降B调和降A调），而杜鹃的叫声“大多在D调”。怀特随后发问：这些不同的音调究竟是“源于不同的物种，还是仅仅来自不同的个体？”

现在我们完全可以去核实这一点，所以我动手尝试了一番。

我的做法。 我从维基共享资源（Wikimedia Commons）下载了39份灰林鸮（tawny owl）录音和14份杜鹃录音，其中大部分来自 xeno-canto 上传的音频。针对每个音频文件，我检测了每个短时间切片中最强的音频峰值频率，并取出现频率最高的值。随后我以两种基准对音符进行了定名：其一是 A = 422.5 Hz（亨德尔1751年音叉的音高，常被用作18世纪伦敦音高的替代基准，尽管其真实数值仍存在不确定性）；其二是现代标准 A = 440 Hz。在查看任何实际数据之前，我预先写下了自己的猜测。

猫头鹰。 我原本猜测叫声大约在 400–500 Hz 左右。但事实并非如此。频谱图显示，雄鸟的叫声在滑落至约 750 Hz 之前，会保持在 900–1000 Hz 附近的音调。雌鸟的“ke-wick”叫声则更高，约为 1,200 Hz。在 31 份可用录音中，单份录音音高的中位数为 905 Hz：在 A = 422.5 时对应 B♭（+19 音分），在 A = 440 时则略低于 B♭。大多数叫声落在 845 到 955 Hz 之间，在伦敦音高标准下处于 A 到 B 之间。因此，“它们的叫声全都是降B调”这一说法完全站得住脚，而那位邻居所听出的音调分布也符合不同鸟类个体之间的差异。现代研究确实可以通过叫声来识别灰林鸮的个体，因此怀特的第二个猜测（“来自不同的个体”）是完全正确的。

一条分岔路（坦白说明）： 我的第一轮筛查搜索了 250–1300 Hz 频段，得出的中位数是 G。这其实是被 340 Hz 以下的低频背景噪声给拉低了。在看到这一结果以及频谱图显示的叫声实际分布位置后，我将频段缩小至 600–1300 Hz。我认为这一调整是合情合理的，但确实是在事后做出的修正。

杜鹃。 杜鹃叫声中的两个音符中位数分别为 660 Hz 和 530 Hz，相差约 3.8 个半音，介于小三度与大三度之间。在伦敦音高标准下，较低的音符是 C♯，与那位邻居所说的“大多在D调”相差不到半个音。较高的音符则更接近 F。在核验之前，我决定对比第一个（较高的）音符，如果按这个规则，关于杜鹃的说法就不成立了。不过怀特并没有明确说明他指的是哪一个音符。

本分析无法解答的局限。 这些录音采集自全欧洲各地，而非1771年的汉普郡（Hampshire）。“伦敦常用音高”本身的波动范围可能在 415 到 430 Hz 之间，仅这一变动就可能让对应的音符名称产生约四分之一个音的变化。此外我本人无法听声音，因此叫声类型是通过查看频谱图而非肉耳倾听来分类的。即便如此，在1771年，一位拿羽管键琴调音管去对比猫头鹰叫声的人，听到的内容似乎与如今麦克风所记录下的并无二致。

数据来源：吉尔伯特·怀特，《塞尔彭自然史》（古腾堡计划），致戴恩斯·巴灵顿（Daines Barrington）的书信第 IX 与第 X 封。录音来源：Wikimedia Commons，“Strix aluco”与“Cuculus canorus”音频文件（主要来自 xeno-canto XC 上传）。代码：基于 numpy/scipy 的短时傅里叶峰值跟踪程序；可按需提供。

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.