Date: 9/10/19 7:23 pm
From: Martha LKJ <marthalkj...>
Subject: [cobirds] Re: What we're hearing during nautical twilight in the Denver metro region
I found your article and recording fascinating. Thank you for sharing!!
Martha Jones, Arvada, Jefferson County

On Monday, September 9, 2019 at 11:43:26 AM UTC-6, Ted Floyd wrote:
>
> Hey, all.
>
> One of my favorite locations in spacetime is nautical twilight
> <https://www.timeanddate.com/astronomy/nautical-twilight.html> in
> residential and urban districts in the Front Range metro region in early
> September. The plains harvest flies, *Megatibicen dealbatus*, have
> largely quieted down by that time, leaving the Twilight Big Three (TBT) to
> do their thing. The TBT are: the low-frequency snowy tree crickets, a.k.a.
> "thermometer crickets," *Oecanthus fultoni*; the mid-frequency fall field
> crickets, *Gryllus pennsylvanicus*; and the high-frequency greater
> angle-wing katydids, *Microcentrum rhombifolium*. Here's the sound of all
> three of them going at once:
>
> https://www.inaturalist.org/observations/32419411
>
> I made that recording in Lafayette, eastern Boulder County, at 8:18 pm on
> Sat., Sept. 7. 2019. The temperature was 71 degrees Fahrenheit. Key point:
> I was in a residential district, away from the marshes and meadows of, say,
> Greenlee Preserve, where many other orthopterans join the fray and
> complicate matters. This is the sound of the city (also the sound of the
> suburbs) in the region. Call it the symphony of the city. The snowy tree
> crickets have a distinctive, musical, pulsating quality; count the number
> of chirps in 15 seconds and add 40 and you have the temperature in degrees
> Fahrenheit. The fall field crickets are higher and shriller, the classic
> "nothing but crickets" of 20th-century television and movies.
> (21st-century, too, perhaps, but I haven't watched TV since about 1990. I
> hear there's something called flatscreen and reality shows??) And the
> greater angle-wing katydids are the spooky "clicky night bugs," like a
> little ghoul--a DIA lizard person, perhaps--chattering its teeth in the
> treetops.
>
> I find spectrograms to be useful for understanding and enjoying natural
> sounds, so here's a spectrogram of the recording above:
>
> [image: Orthopteran symphony.png]
>
> The top panel is, in essence, a measure of how loud the sounds are. The
> fascinating and--for me--somewhat depressing thing is that the katydids
> (indicated by the vertical lines) are unbelievably loud. I don't hear them
> all that well anymore. But my wife and kids tell me they are as loud as the
> flickers that are slowly but surely denuding the house of its siding and
> roofing. The steady pulses, barely visible above the baseline trace, are
> the snowy tree crickets; and the baseline trace itself is the chorusing of
> the fall field crickets.
>
> The lower panel is, if you will, the musical score of the orthopterans'
> songs. A musical score is a plot of frequency against time (really! it
> is!), and this lower panel is precisely the same thing. Different units and
> scales, but it is trivial to "translate" from one notation to the other.
> Anyhow, you can see the high clicking of the katydids (so-called "carrier
> frequency" way up there just under 10 kHz), the mid-range trilling of the
> fall field crickets (around 5 kHz), and the distinctively low-frequency
> grinding of the snowy tree crickets (just under 3 kHz).
>
> There's a nice tutorial in the physic literature on all of this, although
> applied to the songs of common American birds, not orthopterans. The paper
> came out just a week ago:
>
> https://aapt.scitation.org/doi/10.1119/1.5124271
>
> Some of the content is behind a paywall. If you want the PDF of the full
> article, please get with me backchannel, and I'll be happy to send it along.
>
> Or simply enjoy the songs, just as they are! Remember: low, pulsing = tree
> crickets; higher, shrill = field crickets; very high, clicking = katydids.
> And this: Listen in busy neighborhoods; tree-lined boulevards are the best.
>
>
> Ted Floyd
> Lafayette, Boulder County
>

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