Saturday, August 25, 2012

An Extraordinary Cricket Song, Part II

   Tree cricket songs add to the pleasant night sounds during these summer evenings.  Additionally, tree cricket songsters put on a surprising performance if a person has the opportunity to observe them singing.
tree cricket song amplified by hole in leaf
   At dusk, and on into the night, we've been hearing some plaintive tree cricket songs emanating from our fence row.  The source of those melancholy, intermittent trills are Narrow-winged Tree Crickets.  Their song is a medium pitched trill of a few seconds duration followed by a short pause.  With some careful searching I found numerous tree crickets in the trees... singing from between the leaves of our young Walnut trees.
tree cricket singing through hole in leaf
   Tree crickets raise their wings almost perpendicular to their body while singing. Their sounds are produced by rubbing one forewing aginst the other. One wing has a file and the other has a scraper. As these pass over each other they cause the wings to buckle (vibrate) and produce the sound pulse. 
  Most of the cricket photos I have are of singing crickets, but here is a picture of a Narrow-winged Tree Cricket (Oecanthus niveus) at rest.  Here is a link to a website with some information about crickets and a recording of a calling Narrow-winged Tree Cricket and here is another tree cricket website.
 As I mentioned, in our backyard, the tree crickets sing from between the walnut leaves.  I meant that literally.
The Narrow-winged tree crickets seem to prefer singing with their wings aligned in the gap between the edges of two leaves.
This unusual position is no accident.  The crickets are using the leaves to amplify their songs.  
Leaves amplifying a tree cricket song
This is accomplished by using the leaves as an acoustical baffle. As the cricket's wings vibrate they produce sound waves off the front and the backsides of the wings (dipole sound source).  The leaf baffle helps prevent the front sound waves from interfering with the back waves (destructive interference) which avoids cancellation of some of the precious volume of sound these small creatures can produce.
   These little acoustical engineers, the tree crickets, also like to sing through a hole in a leaf.
one secret to a tree cricket song
I suspect the Narrow-winged Tree Cricket is an opportunist... making use of any suitable and properly sized hole that some other creature made.
However, there are some species of tree crickets that chew their own holes which they use as amplifiers.        Most of the time the Narrow-winged Tree Crickets that I have observed just avail themselves to any convenient and suitably sized gap in the leaves.
   The many leaflets on the walnut trees provide exactly what the crickets need for their sound system. Perhaps for that reason,  I have found few tree crickets on the other trees and bushes in our fencerow. Another possibility is the fact that the walnut's low branches overhang the driveway where I can conveniently observe the tree cricket's nightly performances.
I did find a tree cricket singing through the "v" at the base a grape leaf.
Notice the contortions the tree cricket puts itself through while calling... in order to position itself the most advantageously with its chosen sound baffle.
   Those efforts are especially noticeable when the tree cricket uses the edge of a single leaf for its acoustical effect.
   I can hear the tree crickets songs way out across the yard, but when close at hand they can be difficult to hear.  I believe this is because of the directional nature of their "sound system".
   Ordinarily, the various night sounds of the katydids and crickets all blend into a pleasant din that one simply ignores.  However, when one picks out a distinctive call and ponders what extraordinary efforts the songster employed to broadcast that song out into the night...
... each cricket call is an extraordinary song. 
  Those songs are calls for mates, but they call me as well.  A cricket's song calls me to search for the singer in hopes of witnessing an outstanding performance of acoustical ingenuity. 
I think knowing the crickets and their trills is a thrill.

1 comment:

  1. Dana,

    I think reading your posts explaining the wonders of nature to me, is a thrill too !

    ReplyDelete