Monday, March 19, 2018

Cricket Songs: General Characteristics of Pitch and Rhythm



Having looked - and listened – to how crickets and katydids sing, the next step is to explore the nature of their songs. We’ll get more specific later, but I think it’s essential to know the general characteristics first. I’m going to focus on two basic musical elements: pitch and rhythm


Let’s start with the crickets. We can often hear crickets more clearly and more easily because their songs are actually much lower in pitch than most of the katydids. (We’ll explore katydid songs in the next post.)


Pitch


Insect song is not like birdsong. Unlike most songbirds, crickets do not change pitch during the course of a song. They do not create little melodies. (Slowing down their pitches will not create “God’s Cricket Chorus,” no matter what you may have encountered on Facebook.)


Here’s an example:







Notice that the Tufted Titmouse song has two different pitches. It’s a simple song that we could imitate – just in a lower octave than the Titmouse because we humans can’t sing that high. 



One pitch is higher than the other, and the two notes alternate in a simple higher-lower pattern. The rhythm of this short song is repetitious, and then there’s a short pause. After this brief rest, the Titmouse sings the song again (and again and again). 


The Snowy Tree Cricket has a pitch that we could also imitate as long as we sing it in a lower octave.  But notice that I said “a pitch.” Just one. The cricket can’t change pitches in the course of his song like the Titmouse. He can repeat his single note at a very steady rhythm, but it’s just one pitch.



You can see the higher-lower alternation of the Titmouse song in the sonogram, and you’ll also see that the Snowy Tree cricket’s song is a repetition of the same note at a steady rhythmic pace.



As with birds, different species sing at higher or lower pitches from each other. Before we take a look and listen to the wide range covered by all NE Ohio's cricket species as a group, let's start with a quick terminology clarification. 

I’ll be referring to “frequency,” which is a specific indication of how high or low a pitch is, not how often it occurs. The term “hertz” is used as a measure of frequency. 3000 hertz means 3000 cycles per second and is abbreviated as 3000 Hz or 3 kHz – kilohertz. 

I’ll make this more accessible by providing birdsong, human voice, and even piano comparisons to provide a concrete context. For example, middle C on the piano is 261.6 Hz. My general singing voice range is between about 220 and 880 Hz. We’re going to be listening to singers whose performances are far higher than those of humans!



Tree cricket songs resemble the pitch range and clarity of birdsong, which is why I paired the Tufted Titmouse with the Snowy Tree Cricket in my earlier example. These crickets sing between about 2500 and 4000 Hz, and common birds such as the Black-capped Chickadee, Tufted Titmouse, Eastern Bluebird, and Baltimore Oriole sing in the same range. The lower of the two notes in the Titmouse song recording was almost identical to the Snowy Tree Cricket's single pitch: about 3000 Hz. 

I’ve recorded Field Sparrows whose songs ascend from about 3500 Hz up to a little above 4000 Hz. Listen to an example of a Four-spotted Tree Cricket singing at about 4000 Hz followed by a Field Sparrow’s song in the same range:

 






We’re going to listen to smaller crickets with higher songs next. All of them sing above the highest note on the piano, which is only 4186 Hz.


The tiny trigs - just ¼-1/3 inch in size - sound about an octave higher than the tree crickets, ranging between 6000 Hz for the Spring Trig up to around 7000 Hz and above for the Say’s and Handsome Trigs (pictured below.)

Handsome Trig singing





Although quite high, these songs still sound like musical notes. Bird songs in similar ranges include the Grasshopper Sparrow, Henslow’s Sparrow, and Cedar Waxwings (pictured).
 





Ground crickets also sing much higher than tree crickets. Their songs are between 6000 and 7500 Hz. In addition to being very high, many of them sound less musical because the tone quality is buzzier to our ears. The most musical among them – at least in our region – is the Allard’s Ground Cricket with his rapid, sparkling song. The Striped Ground Cricket has a more buzzy sound and a steady, rhythmic "zit-zit-zit" song. This is an Allard's (pictured) and a Striped singing together. 








Finally, here’s a representative example of the entire range of cricket song in NE Ohio: an example that strings together a Mole Cricket, Narrow-winged Tree Cricket, Black-horned Tree Cricket, Spring Trig, Allard’s Ground Cricket, and Say’s Trig.






Rhythm and phrasing


It’s all about rhythm and phrasing with insect songs. Many cricket species have rhythmic patterns we can learn to recognize. Others have long songs that are a continuous stream of very fast notes called a “trill.” 

The Fall Field Cricket and the Jumping Bush Cricket both sing a long series of chirps that may even occur at the same pitch, depending on temperature. What’s the difference? The Fall Field Cricket’s songs will be much faster and have less space between them than those of the Jumping Bush Cricket. (Both are singing at around 5000 Hz in this particular track. Photo: Fall Field Crickets.)





Here’s a Snowy Tree Cricket followed by a Narrow-winged Tree Cricket (photo below). Their distinctly different rhythmic patterns help us identify them in the field, which is helpful because they may be in the same habitat or even in the same tree or shrub.







The Broad-winged Tree Cricket sings a long, very fast, continuous trill without rhythmic pauses; the pitch, as you would expect by now, stays the same throughout. Black-horned and Forbes’s Tree crickets (which look and sound identical) also sing continuous trills, as do Pine Tree Crickets and Four-spotted tree Crickets. This group is a challenge because they do not have rhythmic patterns that help us identify them when we can’t see them, and we’ll address that challenge in greater detail when we explore groups of similar species. 


Finally, listen to these three common ground crickets: the Carolina Ground Cricket, the Allard's Ground Cricket, and the Striped Ground Cricket. They look so similar that it takes a great deal of practice to tell them apart. However, the rhythm of their songs makes the different species quite obvious!






Temperature changes everyone’s pitch and tempo!


Finally, the pitch of all these crickets will be higher in warm temperatures and lower in cool temperatures. Keep in mind that they are cold-blooded individuals. They move much more quickly when it’s quite warm. They can run and jump faster, and they can also move their wings faster and sing higher. 

It’s important to remember that temperature affects all of the crickets and katydids.  The entire insect orchestra will sing faster and higher when warm. As temperatures drop at night, the entire ensemble sings slower and at a lower pitch.

This is the reason we cannot identify crickets by their pitches. The pitch you will hear in a field guide recording is only true at the same temperature as when the recording was made. Here are some examples:


The first is a Snowy Tree Cricket singing at 84F, then 66F, and finally at 61F.

 

Did you notice that the second and third series of songs were  both slower in tempo and lower in pitch? For this species, you can even calculate the temperature by counting the number of chirps in 13 seconds and then adding 40. 

If the temperature is not identical on two adjacent plants or a different part of the same shrub, that small difference will be revealed by the songs of two nearby individuals. In this recording, you’ll hear two nearby Snowy Tree Crickets in the same flowering raspberry singing almost – but not quite – the same pitches. They are not completely in sync rhythmically, either, because the one that’s a bit warmer is singing just a little faster. Yes, they are that sensitive to temperature! You'll hear each one separately, then both together. 





Now listen to the difference in pitch between a Broad-winged Tree Cricket on a warm evening and another at 58 degrees. The frequency drops from 2637 Hz (an E) all the way down to 1661 Hz (a G#). At the colder temperature, it becomes possible to hear the separate wing strokes because he’s moving more slowly. He’s cold, but determined!






Here’s another example: a Jumping Bush Cricket on a warm, late-summer evening and then a chilly night (55F). As they sing slower (as well as lower in pitch), it becomes possible to better hear the individual wing strokes that make up each chirp.

 



This Pine Tree Cricket was struggling to sing when the night temperature dropped from 70F (beginning of this track) down to 61F (end of this track). Eventually, he could no longer continue his steady trill. He finally just stopped.
 






Finally, I have one last cricket/bird pairing to summarize. Remember that Four-spotted Tree Cricket recordings I paired with Field Sparrow?  The Four-spotted sings a continuous trill, but notice that it’s lower at the cooler temperatures and higher at warmer temperatures. The Field Sparrow (a species that would live in the same habitat as the Four-spotted Tree Cricket) has a song that can start lower and ascends. In just one song, the Field Sparrow covers the range of pitches that the Four-spotted sings at 66F all the way up to the 80 degrees. Birds can change pitches within a single song AND their pitches do not change with the temperature.







Our challenge is clear. Each song has just one pitch, but everyone’s pitches rise and fall together with temperature changes. We can’t assume that a recording of a particular cricket will match that same species in the field unless the temperatures are the same.  Rhythmic patterns are very helpful, so tree crickets that sing long, continuous trills are the biggest challenge. In future posts, I’ll offer more specific guidelines for these identifications when we talk about seasons and habitat.


                                Four-spotted Tree Cricket singing in aster flowers.

1 comment:

  1. Wow, this is a very informative post, and great comparisons to birdsong. All features, pitch, rhythm, phrasing, are important characteristics that help us distinguish birds, too - luckily they do not change their pitch with ambient temperature!

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