The Transformed Block Count

by Carl Strang

The developers who built my subdivision, in their wisdom, decided to plant mostly green ashes along the streets. That brilliance has been answered in the form of an insect, the emerald ash borer. This little invasive ash-killer has done a number on my neighborhood. A series of before-and-after shots follows, going around the block route I follow when I do my standard survey of singing insects in the warm months.

Looking north along my street in 2009.

Looking north along my street in 2009.

The same block now.

The same block now.

Turning west in 2009.

Turning west in 2009.

Same view, 2013.

Same view, 2013.

The next block, looking south in 2009.

The next block, looking south in 2009.

And now.

And now.

The final leg, facing east in 2009.

The final leg, facing east in 2009.

Hard to believe it’s the same block today, but it is.

Hard to believe it’s the same block today, but it is.

Most of the tree loss happened over a brief period of time, the second half of summer last year. Ever the opportunist, I made predictions about the response of the three singing insect species common enough for statistical comparisons between this year and last. Greater angle-wings are tree-dwelling katydids, and so I expected their counts to drop. Carolina ground crickets mainly live beneath foundation shrub plantings, so I expected no significant change. Finally, striped ground crickets prefer sun-lit lawns to shade, so I expected their numbers to increase. I was correct on two of the three predictions.

The Carolina ground cricket median count in 2013 was 7, not significantly different from 2012’s median of 5 (Mann-Whitney U-test of the ranks of all the counts led to a z statistic of 2.05, p>0.01). The median count of striped ground crickets in 2013 was 20, that in 2012 was 11. The comparison of ranks produced a statistically significant z value of 3.89 (p<0.01). I was somewhat surprised at the lack of a demonstrable difference for greater angle-wings (z = 1.00, p>0.01). The 2013 median count was 3, less than the 2012 median of 5, but the difference was not as large as one might expect. There were enough surviving trees of other species to sustain a population of the katydids, and also the removal of the nearer trees made more distant angle-wings more audible.

Block Count Summary

by Carl Strang

Neighborhood block counts are a survey method I have developed in my singing insects study. They consist of walks around the block in my residential neighborhood in Warrenville. I record the time and temperature, and count only the insects whose individual songs I can distinguish from the general background of tree cricket and ground cricket songs. I try to include a mix of times, especially early in the season to include cicadas, but concentrate most of the effort after dark when most species are singing. The overall species count in 2011 was 14 (no new species this year).

One of the streets on the block.

Most of these insects do not occur in high enough numbers to permit statistical comparisons between years. The high counts for each species this year were as follows: 1 for fall field cricket, jumping bush cricket, Say’s trig, and Davis’s tree cricket; 2 for Allard’s ground cricket and dog day cicada; 3 for snowy tree cricket, 4 for narrow-winged tree cricket, 5 for common true katydid, 8 for two-spotted tree cricket, 10 for Linne’s cicada, 14 for Carolina ground cricket, 16 for greater anglewing, and 26 for striped ground cricket. Most of these are typical of the past five years. Apart from statistical comparisons to follow, there seems to have been a decline in fall field crickets over that period (high counts of 5 in 2007, 4 in 2006, and 1 in the recent years, but in 2011 that count was on only one occasion).

Only three species occur consistently in large enough numbers to justify statistical comparisons between years. There never have been statistically significant differences between adjacent years in striped ground cricket counts, and the same was true in this year’s comparison with 2010 (overall medians 14.5 in both years; Mann-Whitney U-test, z = -0.14, P>0.01). Carolina ground crickets likewise were not different (median 4 in 2010, 7 in 2011; z = -2.07, P>0.01). Greater anglewing counts did show a statistically significant increase over last year (median 1 in 2010, 4 in 2011; z = -3.30, P < 0.01), and in general they and the fall field crickets have been the most volatile.

Song Peaks

by Carl Strang

My block count data allow me to look at when different kinds of singing insects are most active. I note the time of day for each count, and this year categorized four years’ counts with respect to number of hours before or after sunset.

Two-spotted tree crickets sang the most in the hour after sunset, then continued intermittently through the night.

Sample sizes were 1 count 5-6 hours before sunset, 3 counts 4-5 hours before sunset, 9 counts 3-4 hours before sunset, 13 counts 2-3 hours before sunset, 20 counts 1-2 hours before sunset, 29 counts 0-1 hour before sunset, 61 counts 0-1 hour after sunset, 59 counts 1-2 hours after sunset, 23 counts 2-3 hours after sunset, and 11 counts 3-4 hours after sunset. Some of these sample sizes are small enough to consider the results as tentative (especially for cicadas, which sing before sunset), but on the whole they seem to reflect my more general observations of activity peaks in DuPage County.

Snowy tree crickets peaked 2-3 hours after sunset. Some tree crickets like to nibble on human skin, given the chance.

I found the following peak singing times:  4-5 hours before sunset for Linne’s cicada, 1-2 hours before sunset for the dog day cicada, 0-1 hour after sunset for jumping bush cricket and two-spotted tree cricket, 1-2 hours after sunset for fall field cricket, snowy tree cricket, common true katydid and greater anglewing, 2-3 hours after sunset for striped ground cricket and Carolina ground cricket, and 3-4 hours after sunset for narrow-winged tree cricket.

Narrow-winged tree crickets showed the latest singing peak in my neighborhood, 3-4 hours after sunset.

One particular bias to keep in mind is that some loud singers may drown out others, reducing their counts. For instance, ground crickets are singing at the times when cicadas are active, but I can’t hear them above the cicadas’ loud drones.

Comparative Block Counts

by Carl Strang

In 2010 I made enough counts of singing insects in the small rural town of Culver, Indiana, to compare them to my block counts in Warrenville, Illinois, of the Chicago suburbs.

I walked around similar sized blocks in the two locations, counting the singing insects I heard. This is the south side of the Culver block.

The species count in Culver was 14; differences in species from Warrenville were the absence of Say’s trigs and common true katydids, and the addition of the lyric cicada.

Three species at Culver were abundant enough and showed enough of a difference in median counts to make statistical comparisons worth trying. Culver had more fall field crickets (median count 6, vs. 0 for Warrenville), fewer striped ground crickets (median counts 9.5 and 17 in the period of time covered by the Culver counts), and no statistically significant difference in greater anglewings (median counts 0.5 and 3.5 in Culver and Warrenville, respectively, during the sampling period,).

The Warrenville neighborhood had few fall field crickets in 2010. They were much more abundant in Culver.

I also heard two unfamiliar songs at Culver that may represent additional species. The first of these sang soon after dark on July 31, from a point off the ground and of the speed and pattern of an Allard’s ground cricket, but composed of dry clicks or ticks rather than notes or tones (listening to reference recordings the next day, I thought the most likely possibility was handsome trig).

During a Culver block count on September 4 I heard another unfamiliar song. The temperature was cool, between 55 and 60F, so the song may have been slowed. It had two parts, each consisting of fairly rapid phrases. The first part’s phrases were like doubled ticks, lispy in quality, produced for several seconds. The second part consisted of single ticks, reminiscent of the greater anglewing, lasting much longer (several seconds), and at a distinctly more rapid rate than in the first part. This pattern seems best to fit some member of the subfamily Phaneropterinae, the false katydids.

Block Counts

by Carl Strang

One easy data set to collect in my singing insects study is simply to walk around my neighborhood block (usually when going to my mailbox) and count the insects I hear. For this year I have comparisons between years, a comparison to my new count at my parents’ home in Culver, Indiana, and a consideration of species counts with respect to the time of sunset. Today I’ll focus on this year’s results in my neighborhood.

This photo of my yard is not representative of the neighborhood, in that most of my neighbors are lawn lovers who have very limited shrub and herbaceous plantings.

The overall count in my Warrenville, Illinois, block was 15 species in 2010 (for the complete list go here). No new species were added. Again in 2010 the only species abundant enough for comparisons between years were striped and Carolina ground crickets, and greater anglewing katydids.

Striped ground crickets are named for stripes on the top of the head.

Though striped ground crickets occur in prairies, they really hit their stride in mowed lawns. Not only are they the most abundant singing insect in my neighborhood, their numbers have been very consistent over the years with median counts of 13, 12, 12 and 14.5 in the respective years of 2007 to 2010. None of these differences are statistically significant.

The ticking song of the greater anglewing is a distinctive summer evening sound wherever this katydid occurs.

Carolina ground crickets, which hang out in denser plantings, and tree-dwelling greater anglewings likewise showed no changes between 2009 and 2010 (this year’s median counts 4 and 1, respectively).

Culver Block Counts

by Carl Strang

At the end of July during a visit to Culver, Indiana, I decided to initiate a new block count of singing insects.

This is a method I have been using for a few years around my home in Warrenville, Illinois, to assess singing insects quantitatively. Now I will be able to compare those results to counts from a second location, though with my parents thankfully resuming their independence my Culver counts will be relatively few. I will need to make several counts on each of the days I am there.

The method consists of walking around a residential block, counting the singing insects of each species that I hear.

The first counts at Culver produced results similar to those I have been getting at Warrenville. In both locations, the lawn-loving striped ground cricket is the most abundant species. The biggest difference is that in Culver I heard 9 fall field crickets on the inaugural walk.

I have yet to hear any this year at my Warrenville block, though I have found them there in past years.

Block Count Results

by Carl Strang

Earlier in the season I described my block counts of singing insects, in which I walk around the block where I live, counting the singing insects I hear. In these counts I heard 13 species in 2009, compared to 15 in 2008. The two missing species were the dog day and scissor-grinder cicadas, both of which I heard on my block at times other than sampling sessions.

Only 3 species have been present in large enough numbers to allow comparisons between years. Most abundant is the striped ground cricket, with median counts of 13, 14.5, and 12 for 2007, 2008 and 2009, respectively*. Statistical tests found no differences among years in the striped ground cricket.

Median counts of Carolina ground crickets were 3, 3, and 7 for the three years. The change from 2008 to 2009 was statistically significant. The third species, the greater angle-winged katydid, produced median counts of 7, 1, and 0. The drop between 2007 and 2008 was statistically significant, but that from 2008 to 2009 was not.

The other species I have noted in my neighborhood, in rough descending order of abundance, are two-spotted tree cricket, snowy tree cricket, fall field cricket, narrow-winged tree cricket, Linne’s cicada, common true katydid, Allard’s ground cricket, and a few species I have heard very infrequently: jumping bush cricket, Say’s trig, Davis’s tree cricket and possibly fork-tailed bush katydid.

*For those interested in the technical details, I included only counts in August-October, the months when these species appeared consistently. Total numbers of counts were 49, 46 and 35 in the three years, respectively. I am very conservative in my use of statistical tests. Here I used the large-sample version of the Mann-Whitney U-test, a nonparametric test which produces (ironically?) a z test statistic. Non-parametric tests are needed for count data, and I seldom see anything like a normal distribution in the aspects of nature I study, anyway. Test statistic values for striped ground cricket counts were z = -0.73 for 2007 vs. 2008, and -1.58 for 2008 vs. 2009, both P > 0.01. Again, being conservative, I use the 1% rather than the 5% level of error. Carolina ground cricket counts showed no change between 2007 and 2008 (z = -0.68, P > 0.01), and an increase from 2008 to 2009 (z = -3.32, P < 0.01). Greater angle-wing counts showed a decrease from 2007 to 2008 (z = -3.33, P < 0.01), but no change from 2008 to 2009 (z = 0.32, P > 0.01).

Gadget 1

by Carl Strang

For the most part in this blog I am trying to model methods of inquiry that don’t rely on technology. Our human senses have their limitations, but we can gather enough information through them to answer a lot of questions about our surrounding wild world. Nevertheless, there are occasions when gadgets can help. Today I will feature one of those I have found useful in my field studies of singing insects: my soprano recorder.

Recorder b

I don’t have perfect pitch, but I have a reasonably good ear. I have found the recorder to be especially helpful as I tackle the problem of the arboreal tree crickets (outlined in my earlier post on one of them, the two-spotted tree cricket ). This season one of my goals has been to sort out the songs of the two-spotted, narrow-winged and Davis’s tree crickets. I was encouraged when I noticed that Elliott and Hershberger, in their recent book on singing insects, indicated that these three species should have distinct pitches in their songs. Highest should be the two-spotted, at 3.5 kHz (kilohertz, a quantitative sound frequency measurement), which translates to a pitch of A, the fourth A above middle C. In the middle should be the narrow-winged tree cricket, at 3 kHz or approximately F-sharp, the fourth F-sharp above middle C, 3 half-tones below the two-spotted. I noticed, incidentally, that the distinctive song* of the snowy tree cricket also is indicated to be at 3 kHz, and so I had hopes that this would provide a rough and ready field standard. The lowest of the arboreal tree crickets, according to Elliott and Hershberger, is the Davis’s tree cricket, at 2.5 kHz. This translates musically to the fourth E above middle C, distinctly lower than any of the others. So, recorder in hand, I set forth.

Snowy tree cricket 5b

Snowy Tree Cricket

Two caveats quickly became clear. First, the pitch of a given species is subject to change with environmental temperature, rising and falling as the temperature rises and falls. Second, I have to keep in mind that my own hearing may not well match the measuring devices used to provide the information in that book. In general all species sounded, to my ear, a good 3 tones lower than Elliott and Hershberger suggested.

I have found that to my ear, both two-spotted and narrow-winged tree crickets have songs distinctly higher pitched than that of the snowy tree cricket. At a given temperature, the two-spotted sings one-half to a full tone higher than does the narrow-winged. However, at a given general temperature, narrow-wings range over half a tone of pitch or more. Whether this is because the microclimate is different where individual crickets are singing, or whether this is something they are controlling, I cannot say. It means, though, that I have to rely as much or more on the temporal pattern of the song to distinguish these two species.

Narrow-winged Tree Cricket

Narrow-winged Tree Cricket

Narrow-wings sing with a steady pattern of trills and spaces, with trills of equal lengths and spaces of equal lengths, and the spaces are significant at a second or so duration. Two-spotteds sing at a little higher pitch on average, have trills of varying lengths including some often lasting well over 5 seconds, usually with at least some pauses that are very brief, as though catching a quick breath.

I recently heard, on my neighborhood block count, what I believe must have been a Davis’s tree cricket. The insect was high up in a tree. Its trills were variable but generally very long, with only occasional odd interruptions. Spaces were short. Significantly, the pitch was down at A-flat, low for the temperature, which was 70F. Based on my recorder tests, at that temperature I would expect snowy tree crickets to be singing at B or C, two-spotteds at the E above that, and narrow-wings at C to E. So, the recorder is a helpful tool, but in distinguishing the songs of these crickets I find that the pattern of their song is more reliable than the pitch.

*You know the song of the snowy tree cricket, even if you live outside its range. In the movies, whenever the director wants to convey a calm nighttime mood, there will be a snowy tree cricket in the sound track. The song is a pulsing tone, varying with the temperature so that if you count the notes in 15 seconds and add 40, you have the temperature in degrees Fahrenheit. Though the narrow-winged tree cricket’s song likewise is a regular pulse, the tones are on the order of 2 seconds’ duration with a 1-2-second space between. Unless the temperature is very cool, the snowy’s song is much faster.

Block Counts

by Carl Strang

Sometimes I collect data without a particular question in mind, on the possibility that I may learn something that guides a future inquiry. My block counts of singing insects are an example.

Block count 1b

My mailbox is a block away from my home. When the singing insect season arrives in the latter half of July, I begin going around the block the long way to retrieve my mail. The above photo shows the first side of the block as I head north. Next, I turn the corner and head west.

Block count 2b

I vary the starting time, record that along with date and temperature, and count the number of individuals of each singing insect species I hear along the way. Here is the view as I turn south.

Block count 3b

This neighborhood may not look like much, but I have heard a total of 14 species here from 2007 to date, including field crickets, bush crickets, trigs, ground crickets, tree crickets, true katydids, false katydids and cicadas. These data allow me to get some understanding of how species vary in numbers between years, and how their singing changes over the season and with time of day. Once I have picked up the mail, here is the final block as I turn to home.

Block count 4b

One pattern I would have missed without the discipline of the block count is a pause in singing among the cicadas in late afternoon, followed by a big push as light fades toward dusk. I have documented the arrival of a new species, the jumping bush cricket, in the neighborhood. Striped ground crickets and greater anglewing katydids were the most abundant singers in 2007, but while the stripeds also were the top species in 2008 there was a big drop in numbers of singing anglewings. It’s a little early to say much about 2009, but so far there seem to be more Carolina ground crickets than in the previous two years.

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