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:
Press the arrow key:
– 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:
Press the arrow key to stream live:
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).
Tim, I would say you got a pretty good result (68.4 vs. 65). Two things occur to me: (1) for the same temp. is the frequency independent of cricket size? and (2) would relative or absolute humidity play a role in frequency emitted? A nice experiment you did. I have a thermometer in a tool box somewhere. I calibrated it at one point using an ice bath and steam.
Jim
Thanks Jim, although if you look again you’ll see the 68 is before the constant ’40’ is added in the formula; so it’s not such a good fit on that basis.
But you’ve spotted two more variables I didn’t list and which might well affect the result: cricket size and humidity. Major research project needed to check all these variables out!
Thanks for your interest in my Tweet.
A few comments.
My formula was tested for all crickets I have ever heard chirping harmoniously in the Northeast USA, from NY through New England. And I have found it accurate to a half-degree from 60 to 90 degrees. In that experience I note that the cricket sounds I heard registered a double beat, much like a human heart. So you may have been double counting. (Although your sound map shows not evidence of a double signals.) if we assume, for the moment, double counting, then your chirps in 15 seconds come to 33, or so. Adding 40 brings you to 73 deg F.
Another point: The Sun heats the ground, not the air. And the ground in turn heats the air via IR. With the reverse happening overnight. So the air temperature at an “official” height above the ground is rarely the same as that for ground-hopping insects. I would guess your thermometer was not ground-level with them when you took the reading.
Yet another point. Most crickets I have ever heard do not chirp in harmony. More a cacophony. Which precludes sensible temperature measurements from being taken. In my 140 characters, I specifically called for crickets “chirping in harmony” for the experiment.
Apart from the above details, two facts remain.
1) My cricket Tweet was not (and are never) a retelling of something I heard, but the consequence of experiments I conduct or information I independently verify.
2) Your blog entry above is a model of skepticism and analysis — especially with regard to sources of uncertainty. Imagine how much farther along the world would be if everyone confronted new information in this way. If interested, my attempts to do the same appear here:
Part 1
http://tinyurl.com/29nhedu
Part 2
http://tinyurl.com/2am86o4
Thanks again for your interest (and healthy skepticism.)
-NDTyson
New York City
Neil, thanks for your thoughts, and for taking the post’s message in the intended spirit: a warning against accepting ANY claims unquestioningly at face value. I think all your points are valid and we’re pretty much aligned.
A little more digging in the literature shows there most certainly is a chirp/temp relationship, but it’s highly sensitive to variables – especially the species of cricket.
The University of Nebraska-Lincoln Department of Entomology website http://entomology.unl.edu/k12/crickets/temperature.htm
discusses early work and species-specific equations proposed by A.E.Dolbear. Where N is chirps/minute (rather than per 15 seconds) and T=temperature in F:
Field Cricket: T = 50 + (N – 40 / 4)
Snowy Tree Cricket: T = 50 + (N – 92 / 4.7)
Katydid: T = 60 + (N – 19 / 3)
For a hypothetical chirp rate of 150/min, these give T=77.5F, T=62.3F, T=103.7F respectively: a maximum difference of 40 F.
Applying them to my experiment. If the specimen is a Snowy Tree Cricket (which in California it could be) chirping at (4*68) or 272 chirps/min, then Dolbear’s middle equation above predicts T=88F: closer to the 65F actual, and closer still to 76F measured in a later experiment with similar chirp rate. As this second test was indoors, the air/ground temp. diff. you refer to should have been lower. Of course, with no i.d. on the cricket, this is just hypothesizing to reach a desired fit; but at least some quantified feel for the errors listed in my post and the comments is coming out.
I’m leaving cricket country shortly, so no more experiments planned.
Thanks again for your comments and the links.
Tim