by Carl Strang
Those of you on the mailing list for my annually updated guide to the singing insects of the Chicago region would look in vain for northern wood crickets in last year’s edition. I simply wasn’t aware that they could be here. While preparing for the Hills of Gold bioblitz, however, I found that their range extends into our region. I had not included them in the hypothetical list because initially it was directed toward DuPage County in Illinois, and wood crickets never have been found in northeastern Illinois. I gained some experience with wood crickets in the bioblitz, and the sound recordings I made there proved to be of the northern wood cricket, Gryllus vernalis. Study of the relevant scientific paper (Yikweon Jang and H. Carl Gerhardt. 2006. Divergence in the callling songs between sympatric and allopatric populations of the southern wood cricket Gryllus fultoni [Orthoptera: Gryllidae]. J. Evol. Biol. 19: 459–472) indicated that the 2-chirp-per-second, 3-pulse-per-chirp, songs coming from leaf litter in forest habitat, were of northern wood crickets. Southern wood crickets, the other possibility, would have had faster chirps at that temperature.
Last week’s vacation survey trips went so well, despite two days lost to rain, that I had Saturday available to seek northern wood crickets the Indiana portion of the Chicago region (I had not found them in the Illinois, Wisconsin or Michigan excursions). My first two stops, in St. Joseph County’s Bendix Woods and Fulton County’s Judy Burton Nature Preserve, were fruitless. Mid-afternoon brought me to the Winamac State Fish and Wildlife Area in Pulaski County, and I drove the gravel roads until I found one of the parking lots in a forested spot. Immediately I heard the chirps of Gryllus crickets, and I dug out the Marantz sound recorder. As I recorded two different crickets I believed I was hearing 3 pulses in the chirps, as had been the case at the bioblitz.
This was where the cricket in the recording shared below was located.
I would have liked to try and flush out one of the singers, but as the photoflash lighting in the photo suggests, it was getting dark fast, and I barely reached the car before the downpour hit. I tried to get around the storm by driving to the Jasper-Pulaski Fish and Wildlife area, but no dice, and I had to call it a day. So, here is a cut of the stronger recording:
Can you distinguish the 3 pulses that form each chirp?
The visual rendition of the recording clearly shows the 3-pulse chirps, but they are being produced at a 4-chirp-per-second rate.
This might have been confusing, given that the southern wood cricket, not yet known from northern Indiana, more typically has a 4-chirp rate, but the soil temperature was very warm, at nearly 80F, and the scatter for vernalis in Jang and Gerhardt’s graph extends to 4 chirps at that temperature. Also, the dominant frequency was 5.9kHz, good for vernalis but pitched way too high for fultoni at any temperature. So, I am content for now that I have established a present-day northern wood cricket presence in the region. One goal for next year will be to seek them in more locations, make more recordings, and get a better sense of their song features in this part of their range.