Can you tell the temperature from how fast crickets chirrup in the evening?   Neil deGrasse Tyson thinks so, according to this Tweet yesterday evening:

Sounds like a great idea, and as I’m in the foothills of the San Gabriel mountains – cricket central by my standards  – I’ve tested tested out the theory. 

Dr Tyson is not the first person to suggest you can tell the temperature with a cricket, and he’s only having a bit of fun, so in the worst case he’ll be guilty of spreading, rather than generating, misleading information ;-).

Armed with a  digital recorder and a laboratory thermometer, I quickly found a suitable subject.  The temperature read 65 degrees Fahrenheit.   This is what the chirruping sounded like:

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– Cricket at 65F, 20.40hrs

From this sample, using only my ears, I counted 67 chirps in a 15 second period (it’s tricky counting that fast, but I found I could do it by checking off groups of 8 chirps on my fingers).  According to Dr Tyson’s formula, that gives a temperature of 67 plus 40 = 107 F; a whole 42 degrees above the actual temperature.

Why the difference?

We’re doing science here, which means there’s a whole load of stuff to check out before rushing to condemn Dr Tyson for inaccurate tweeting.

• Was it indeed a cricket I was listening to? Sounded like one, but I didn’t actually see it.
• Was Neil referring to a specific type of cricket, but the 140 Twitter limited the detail he could provide?  If he’s missed out a division factor of 2 on the cricket count, that would put my number in the right ballpark.
• Did I listen to the cricket long enough?  Was it in a cricket warm-up or warm-down mode?
• Was my thermometer broken?  Ideally I’d have two or more to check, calibrated against a standard.  But I don’t think it was the problem.
• Could the cricket be hiding under someone’s air-conditioning unit outlet?  This isn’t so far fetched actually.  We have one in the house at the moment living under our fridge because it’s warm.
• Was my sample large enough – both in terms of number of recordings and number of crickets?  I did make four separate recordings and (for now take my word for it) they were pretty similar.  That said, I should really come back over a number of evenings at different times to be sure – right?

Well, in the longer term the sample could get large, as I’ll probably be listening out for these things obsessively for the rest of my life now.

What is a chirp?

Meantime, I wondered if the explanation was down to the definition of a ‘chirp’.  I convinced myself the chirps I had recorded might be doubling up; maybe something the cricket was doing with its legs: ‘chirp-chirp’, ‘chirp-chirp’, etc. – each ‘chirp-chirp’ counting as one ‘chirp’.  Are these double chirps that Neil counted as single chirps?  Was it an issue of resolution and my ears?   To find out, I slowed the recording to 0.19 times its normal speed and re-recorded a sample to get this:

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and a waveform looking like this:

Interestingly, what you hear on the playback isn’t ‘chirp-chirp’ at all; but ‘chirp-chirp-chirp’.  And it doesn’t help us, because each group of three sub-chirps only makes up a single one of our original chirps.  And there is no indication of a slower beat or modulation that would yield a lower chirp count.  My original estimate remember was 67, and if you count the groups on the expanded trace above you’ll find there are 13 in 15 seconds on the slowed down trace or, correcting for the factor of 0.19, gives us 68.4.  Virtually where I started.  The cricket still says it’s 107F when it’s only 65F.  (BTW – you can also hear another animal making an even faster noise in the background.)

Conclusion

In conclusion, accepting all the experimental limitations and caveats listed above, this test alone does not inspire confidence in the formula, and hence, the value of the tweet.

But hey, on the bright side we’ve all learned some possibly quite useless information about crickets, plus, more importantly, something of the pitfalls to watch out for in chronological cricket research (or any research for that matter).