Prairie Tree Cricket

October 10, 2012 at 6:09 am (singing insects)
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by Carl Strang

Recently I shared the story of a tree cricket that I suspected may be a prairie tree cricket. Last week I caught a second one which confirmed the identification, at least as far as I can tell.

As before, I put him in the freezer for a few minutes to immobilize him for photos.

Like the first, he was pale, and his extremities were brown rather than the black of a black-horned or Forbes’s tree cricket.

Beneath, he was dusky on the underside of the abdomen, but not black.

The critical feature is the spotting on the first two antenna segments.

In this one there was none of the smudging that fuzzed one edge of one of the spots on the first cricket. The spots on the first segment were large and fused. The spots on the second segment also were thick.

I was concerned that the pixilation in the photos might be distorting the appearance of spacing between the spots on the second segment, so I took the added step of examining them through the magnifying glass. The spaces were indeed being exaggerated by the camera. This further supports the case for prairie tree cricket.

So now I have the impression that all four species in the nigricornis group of meadow-dwelling tree crickets are present (I have found the four-spotted tree cricket in a few locations), and all may be common, in northeast Illinois. The prairie tree cricket, once a western species, has spread east thanks to agricultural practice. After catching the subject of this post I have had a devil of a time trying to get more (they seem to be staying close to the ground for warmth), so I may not make more progress in quantifying the relative numbers of the species this year. Unfortunately the pulse rates of prairie and black-horned tree cricket songs are nearly identical across the range of temperatures in which they sing. Otherwise I could do the survey entirely with recordings. The four-spotted seems to prefer grasses, but song perches for the other three are goldenrods, asters and even woody plants, so there is little to distinguish them in habitat preference. As for monitoring practice, it looks like this will simply have to be a category “nigricornis group” rather than a count of the separate species.

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Learning to Identify Insect Songs

September 27, 2012 at 6:12 am (methods, singing insects)
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by Carl Strang

One of the obstacles to a singing insect monitoring program is the large number of various songs that need to be learned for identification. This is not really much different from learning bird songs for breeding bird monitoring, however (except that the total number of species is smaller here). Instead of being daunted by the entire process, it is possible to take the learning process in stages, beginning with the songs that are common and easy to recognize, the ones you have been hearing all along but simply didn’t have the species labels. Here is a list of a dozen suggested species to start with in the first stage: spring field cricket/fall field cricket (their songs are identical), Allard’s and striped ground crickets, snowy tree cricket, common true katydid, black-legged meadow katydid, greater angle-wing, round-tipped conehead, dog day cicada, scissor-grinder cicada, and Linne’s cicada (for more information on these species, try the tags at the head of this post).

Snowy tree cricket, one of the species on the starter list

This list and those that will follow are for northeastern Illinois and northwestern Indiana. There would be substitutions in other parts of the country (I encourage readers elsewhere to make comments here with their own suggestions). Go to reference recordings of these species’ songs, either on-line at the Singing Insects of North America website or through the CD that accompanies the Songs of Insects book. It is not too late this year to hear many of the species on this list on the warmer days, though some are finished or nearly so.

My recommended species list to focus on in the second stage of learning consists of 8 species and groups of species: greenstriped grasshopper, gladiator meadow katydid, Roesel’s katydid ( three species that sing relatively early in the season), and then later, Carolina ground cricket, Say’s trig, sword-bearing conehead, two-spotted/narrow-winged tree crickets (no need to worry yet about separating the two), and the meadow tree cricket group (3-4 species whose songs are essentially identical to the ear and will remain so).

Roesel’s katydid is a species from the second-stage list.

This list of common species either will take you to additional, though still readily available, habitats, or else require a little more of a practiced ear (which practice you got with the first species group). In particular, seek out and spend some time getting familiar with the songs of the Carolina ground cricket and Say’s trig. They need a little more effort to recognize in the field, but once you have them, they will be touchstones for many other species (much as robin songs are for learning bird vocalizations). If you are starting now, you might push the Carolina ground cricket to the first list, as it is one of the few species singing on the cooler days and evenings.

Once you have mastered the second list of species, you are ready for the more subtle distinctions needed to distinguish the songs in the third species list. This includes separating out the song of Linne’s cicada from similar songs by the lyric cicada, and in some areas, swamp and/or northern dusk-singing cicada.

Linne’s cicada

Also, by this point you are ready to distinguish the two-spotted tree cricket song from that of the narrow-winged tree cricket. Also, the broad-winged tree cricket should stand out now from other long-trilling species. In addition, you no doubt have noticed and begun to puzzle out other species that are more idiosyncratic in their distribution or smaller in numbers that you have encountered in your favorite places.

And that brings you to the fourth stage, learning the songs of whatever remaining species may live in the area you wish to monitor. For this you will need a regional guide. In the Chicago region, you can meet this need with the guide I am developing. It is available for free as a .pdf e-mail attachment. Simply request it at my work e-mail address: cstrang@dupageforest.com

As you are learning and listening, pay attention to which songs you can hear clearly, and at what distances, and which are marginal. This will inform the limitations you will need to address or acknowledge in your monitoring.

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Toward Singing Insect Monitoring: Wall of Sound

September 26, 2012 at 6:04 am (methods, singing insects)
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by Carl Strang

A few days ago I began addressing the challenges to developing a monitoring protocol for singing insects. The biggest single difficulty is, as I described, differences in peoples’ ability to hear different pitches of sounds. Frogs and birds, the other organisms monitored by their songs, vocalize well within the hearing range of most people. Not so with singing insects.

It takes time to learn to recognize the various songs, but a learning period is part of every monitoring program. Also, monitoring will need to be done day and night because different species sing at different times. Apart from these relatively straightforward aspects, there are at least two other difficulties to overcome that are peculiar to singing insects. One of these is the lack of a vocabulary for describing insect songs. This will come with time, as different people come up with creative ways to communicate. For instance, several times I have heard people likening the tick-and-buzz pattern of the generic meadow katydid song to the sound of a sprinkler set to bounce back rhythmically to its cyclic starting point every few seconds.

Carolina ground cricket, one of the contributors to the wall of sound (though not this particular female, of course).

The final challenge is what I call the wall of sound. This is especially true at night, when the greater number of species and especially of individuals all are singing at once. In particular, many of the common tree crickets and ground crickets have more or less continuous trilling songs that blend to produce a collective mass sound that seems largely undifferentiated. I have a solution that works for me, and perhaps it could be made part of a protocol. When I do my block counts at night, I count only those individual singers that are close enough for me to distinguish clearly as I walk along. I ignore the wall of sound at large. For the most part this gives me a good sample of the species producing that wall, along with the others whose songs are more easily distinguished.

Singing black-horned/Forbes’s tree cricket, another element of the wall.

This isn’t a neat and perfect solution, however. Some of the long-trilling tree crickets have songs that cannot be separated from one another by ear. Others, and I am thinking here specifically of Davis’s tree cricket in my area, usually sing high enough in the trees that their songs are completely buried. Individuals can be distinguished only on the rare occasions when their song perches are low in the canopy (in such cases the Davis’s song is low enough in pitch to stand out).

As should be clear by now, if a singing insects monitoring program is to be comprehensive, it can’t be based on point counts, as is the case in breeding bird surveys and frog monitoring. It will have to be based on a route, as in dragonfly or butterfly monitoring. In conclusion, I think the elements are in hand to produce a workable protocol for a singing insects monitoring program. The main thing missing is enough people sufficiently interested that they will put in the time to learn the songs. Tomorrow I’ll suggest a learning program that will help people to learn insect songs in readily digestible stages.

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Toward Singing Insect Monitoring: Dominant Frequency

September 19, 2012 at 6:07 am (methods, singing insects)
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by Carl Strang

When I conduct workshops or lead field trips on singing insects, people commonly ask about monitoring protocols. We have well established monitoring programs in the Chicago area for birds, frogs, butterflies, dragonflies and damselflies, plants and probably other groups I am forgetting at the moment, so how about singing insects? My answer usually revolves around the fact that different people hear singing insects differently, and this obstacle is a challenge that has yet to be solved. An important variable here is that different people hear different ranges of sound frequencies, and commonly older folks (like me) lose the ability to hear high-pitched sounds. Recently I decided to try to get a quantitative handle on this pattern, using my experience as a gauge. I went to the Singing Insects of North America website and The Songs of Insects book by Elliott and Hershberger, and lifted out the dominant frequencies sung by the species in the Chicago region.

A male short-winged meadow katydid, one of the small meadow katydids, whose song has a dominant frequency of 13 kHz.

Most singing insects produce a range of different sound frequencies when they sing, a buzz for instance consisting of a mix of many low- to high-pitched sounds. Different sounds within the mix have different energies or volumes. The dominant frequency is the loudest one in a given species’ mix. Looking at just the dominant frequency, I see that the various local species range from 1.3 to 17 kilohertz (thousands of vibrations per second, a measure of the pitch or highness/lowness of a sound). I can hear every species with a dominant frequency below 13 kHz. In fact the only species I cannot hear at all are the small meadow katydids (the members of genus Conocephalus), which sing in the 13-17 kHz range. Children and young adults can hear these, I have found. A simple, if expensive, work-around is the SongFinder device.

The long-spurred meadow katydid is my marginal species, at 12 kHz. I can hear them from close range in the woods if there aren’t a lot of competing sounds. Interesting to me is the fact that I hear them clearly at the Brookfield Zoo, where they are fairly common. I doubt that the zoo’s long-spurreds have lower dominant frequencies. My best guess is that the relative lack of other sounds in that range, plus the amplification of the songs reflecting from sidewalks and buildings, increases my ability to hear them there.

Long-spurred meadow katydid, my marginal species

Another related variable is a person’s ability to pick up a sound from a distance. Roesel’s katydid has a dominant frequency of 15 kHz. I can still hear them, but less well with each passing year, and I have to be closer to them. Children and young adults easily pick them up earlier in the song and at a much greater distance. Probably what I hear is not that dominant frequency but the lower part of the frequency range included in Roesel’s buzz. Recently I learned that young adults can hear common meadow katydids, dominant frequency 10 kHz, at a much greater distance than I can, though I hear them clearly if I am within, say, 30 feet.

Common meadow katydid

I think that monitoring protocols are possible to develop, but clearly these are variables that will need to be taken into account. There are other obstacles as well, which I will address at another time.

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A Salute to the NYC Cricket Crawl

October 30, 2009 at 6:07 am (methods, singing insects)
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by Carl Strang

When I began to study singing insects a few years ago, one of my hopes was that I would be able to develop protocols for a monitoring program. I was a participant in the dragonfly monitoring group, and I was aware of hearing-based monitoring programs for frogs and breeding birds. In subsequent years I have found that there is no clear way to comprehensive, all-species monitoring of singing insects. Because of the odd pitch ranges and harmonics, different people hear insect songs differently. For example, older people like me begin to lose their capacity to hear higher pitches, and need to rely on devices like the expensive Songfinder to hear some species. There are many insect songs to learn, in comparison to relatively few frogs and toads. Though the number of breeding bird species is greater, birds are popular. Few people will make the kind of effort needed to learn so many insect songs.

Fall field cricket female 1b

I was interested, therefore, to learn of a group in the New York City area which has come up with a different approach to singing insect monitoring. They call it the Cricket Crawl. They selected a date, September 11, on which they asked people to go out at night and listen to insect songs for one minute at one or more places, then report locations and species heard to the web site. Key to their plan was limiting the focus to seven species of insects with loud, distinctive songs that nearly everyone can hear. They acknowledged that others “form the background of soft churrs and trills that emanate from a series of different small ground and tree crickets.”

While results are not complete as of this writing, Sam Droege and other organizers immediately picked several patterns from the data. For instance, the fall field cricket (photo above of a female) proved to be the species most tolerant of the broad range of urban environmental conditions. The most common katydid was the greater anglewing (photo below).

Greater anglewing 4b

The species of greatest interest was the common true katydid, which historical data indicated at one time had become scarce or even extirpated locally. The September survey found several local populations, some of which may have become established from eggs transported on nursery stock from other parts of the country.

As I continue to ponder possibilities for insect song monitoring, the success of the Cricket Crawl will remain in mind as worth considering.

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