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Monthly Archives: December 2019

Insect Songs and Sound Maps

By Molly Fava

(Molly was an intern with the Farmscape Ecology Program from June – December of 2019)

 

If you are like me, one of the first things you notice as the weather starts to cool off is just how quiet it is when you walk outside.  The birds have stopped chirping, the frogs have stopped croaking, and the insects have stopped calling.  Now that we are experiencing the long, cold, winter nights, you are probably missing those beautiful sounds of summer.  However there is one good part about the darkness creeping in earlier and earlier in the evening: now you have extra time to catch up on your Farmscape Ecology reading!  You may not be able to hear those summer sounds right now, but you can still learn about them!

false katydid sp.

A species of so-called ‘False Katydid’.

 

Insect Songs

Let’s start with some basics: can insects actually even sing?  Some insects, like crickets, katydids, and grasshoppers, can make sound and communicate, but they do not vocalize like humans or birds do.  The main way that these insects (Orthoptera) create sound is through stridulation.  Stridulation is the rubbing together of two body parts, which are modified for sound production.  In crickets and katydids, a sharp edge, often referred to as a scraper, at the base of one front wing is rubbed against a bumpy edge, often referred to as a file, at the base of the opposite wing (view image of file and scraper at songsofinsects.com).

black horned tree cricket stridulation

Black-horned tree cricket with wings raised during stridulation.

Crickets and katydids lift their wings and move them back and forth to run the scraper across the file, which creates the chirping and buzzing that we associate with insect sounds.  Grasshoppers also use stridulation for sound production, but most grasshoppers rub their leg against the forewing to create these sounds rather than using wing movements like crickets and katydids.

grasshopper femur

Great view of a grasshopper’s hind femur, which it rubs against the forewing in order to produce sounds.

Insects create these sounds in order to communicate with potential mates, making other individuals aware of their species, location, and even their quality as a mate.  As insect songs are primarily used for mating purposes, in most species only the males produce songs.  However there are a few species where the females will produce short response clicks and chirps back to the males.

 

Why care about insect songs?

Hearing the melodious songs of insects through the days and nights stimulate nostalgic recollections of summers past, but those songs can do so much more for us than just spark memories.  They can also provide us with knowledge about the insect communities present in different areas.  Every species of singing insect has its own unique song that they use to communicate with other individuals of their own species.  These songs alone can allow us to identify what insect species are located throughout various landscapes.

In order to get a good understanding of what singing insects are present in an area, it is helpful to create recordings of their songs.  Recordings alone can be great to listen to, but they may not always provide a clearer picture of what we are hearing.  So to really break down these recordings and understand the insects, we create spectrograms.  Spectrograms are graphical representations of sound frequencies over time.

striped ground cricket spectrogram

This is the spectrogram of a Striped Ground Cricket song (recording from Singing Insects of North America).  The calling frequency (in kHz) is represented on the y-axis, while the time (in seconds) is represented along the x-axis.

Spectrograms let us look at and read insect songs in somewhat the same way we would read a piece of music.  Identifying the frequency of an insect call is just like knowing which note is being played.  Identifying the number of pulses per second in an insect call is the same as knowing how many notes are played in a specific measure.  So with this ability to identify the notes and count the beats, we can recognize exactly what song we are hearing.

general spectrogram

The brighter colors on the spectrogram represent louder noises.  We have outlined one insect call in red.  Its calling frequency is around 5 kHz, and there are about 2 chirps per second.  This call is most likely a Fall Field Cricket.  The other bright green areas in the spectrogram represent songs coming from other species of singing insects, as well as ambient noises in the recording.

Identifying the song really just means identifying which species is singing, but creating a spectrogram of a recording produced in a pasture that has many different sounds may show us a whole combination of species all singing within that area.  If one recording can tell us this much about a singing insect community, aren’t you curious about what else it can tell us?

 

Sound Maps

In order to learn even more from these recordings, we decided to start creating sound maps.  Sound maps display the power of sounds over a landscape.  They demonstrate where we would hear sounds coming from if we were there standing in that landscape listening for ourselves.

To create the sound maps we had in mind we had to collect a lot of recordings, 480 to be precise.  So we found a shrubby Hawthorne Valley pasture that was very busy with insect songs, and then we identified the areas within that pasture that we wanted to record.

aerial photo of site

The area outlined in red is the general location of our sound mapping recordings in a shrubby Hawthorne Valley pasture.

We set up 20 recording units, spaced out 50 feet from each other in a grid.

recording grid

Each yellow dot represents the location of one of our recording units.

setting up recording units

Kenny Fowler, field technician, sets up one of the recording devices.

Each of these recording units was set to record for two minutes, on the hour, every hour, over a 24-hour period.  We attached the microphone to a stake about a foot off the ground in order to limit interference with vegetation and orient all the microphones in the same direction.

Jules1 unit

This shows one of the recording units set up in the field with the microphone (circled) attached to the green stake.  All twenty of these units were created by Jules Madey, and this project would not have been possible without all of his hard work.

After a full 24 hours of field recording, we created spectrograms of the recordings we collected.  The spectrograms helped us identify which types of insects were calling throughout the area we monitored.  Although each species of singing insect has its own unique song, it can be difficult to automatically select these songs out of the spectrogram using software programs.  In the Northeast, there are about 55 species of katydids (about 20 of these are ‘traditional’ big, green, leaf-like katydids; most of the rest are Meadow Katydids, which more resemble grasshoppers with hair-like antennae) and about 40 species of crickets (including 9 tree crickets).  As the air temperature changes over a 24-hour period, so does the frequency of each of these species’ songs.  So our sound maps represent songs from types of singing insects (i.e. tree cricket, field and ground cricket, katydid) rather than representing songs from individual species (i.e. Black-horned Tree Cricket, Common True Katydid).

recording unit collection

Dylan Cipkowski, biologist, and Zion, good boy, collect recording units after the 24-hour recording cycle.

Using a software program called Raven, which is also the software used to create our spectrograms, we were able to identify the relative pressure of the insect sounds in each of our 456 recordings (one unit malfunctioned).  Then using ArcGIS software, we used radial basis functions interpolation techniques (available with Geostatistical Analyst extension) to map the relative pressure measurements of various sounds over the landscape.  Interpolation uses the pressure data and the location data of each recording unit to approximate the sound pressure in areas between each recording device, allowing us to see where the insects are calling.  Warm colors on our maps represent high pressure (i.e. louder) sounds.  Cool colors represent low pressure (i.e. quieter) sounds.

tree crickets calling at 9pm

This image shows the locations of calling tree crickets at 9pm.

Then we were able to use these maps to compare different aspects of the insect sounds, like what groups were calling at certain times of day.

trial-1-at-12pm.png

These maps show the calling patterns of three types of singing insects at 12pm.  The field and ground crickets are extremely loud at midday compared to the fairly quiet tree crickets and the moderate noise level of the katydids.

Or, how the locations and sound pressure for one type of insect change throughout the day.

fieldef80a2ground-crickets-3x-of-day-e1577118195555.png

These maps show the calling patterns of field and ground crickets at three different times of day.  They are calling from different areas at various times of day.

Or, which habitats each type of insect is using.

3insects-at-12am-with-habitat-types-e1577116458645.png

These maps show the calling patterns of three types of singing insects at 12am over the different habitat types in the pasture.  The areas of the map covered in gray horizontal lines represent the tree and shrub covered land, while the uncovered areas of the map represent the open grassland.  At this time of day, the loudest calling from the tree crickets seems to be coming from the tree and shrub covered areas, while the loudest calling from the field and ground crickets seems to be coming from the open grasslands of the landscape.

 

lined up Jules1 units

Two recording units are clearly visible, with a third deep in the background.  Both the open grassland and the tree and shrub-covered areas of our study site are visible in this photo.

Our immediate goal was to create an ‘animated soundmap’ video showing how the sound landscape evolved across 24-hours, and here it is!

 

Future Efforts

These maps represent our very first attempts to make 24-hour sound maps, and this is only the beginning of our sound mapping efforts.  We are working to increase funding to our sound-mapping project in order to build more units and to apply this technology to other types of research.

We hope to focus on questions of (1) ecology, like ‘how does habitat use differ among the species?’, (2) farmscape management, like ‘how does the abundance of these creatures differ between organic and conventional orchards?’, (3) transmission arts, like ‘how do people’s perceptions of their sound landscape change after they see maps like these?’, and (4) phenology, like ‘how do these calling patterns change throughout the season?’.

 

Importance of singing insects and sound maps

At this point you might still be wondering why these maps, or even just these insects, actually matter.  Singing insects are inherently valuable as part of the wondrous diversity of life on Earth.  However, they also interact with lives of other organisms, including humans.  Often times crickets, katydids, and grasshoppers are thought of as pest species.  While this is sometimes the case, they are only able to cause significant damage to crops when there is a massive local abundance of these insects.  Grasshoppers tend to be the most damaging to crops, but crickets and katydids tend to be omnivorous, meaning they feed on both plant material and other insects.  We see crickets showing up at army worm egg baits we set up during field work, so they could even help control some pests.  Besides occasionally eating individuals of their own species, crickets and katydids are an important food source for a lot of other organisms as well.

Many insectivorous birds rely on Orthoptera (crickets, katydids, and grasshoppers) as a large portion of their diets.  Some of these birds rely on them so heavily that their survival and reproductive success may be directly linked with the populations and abundance of these insects.  One species of bird that depends on Orthoptera is the Eastern Meadowlark, which is facing rapid population declines.  These are grassland-breeding birds, so the primary conservation concern is nest destruction from mowing and grazing, which have also been shown to cause large declines in grassland Orthoptera abundances.  With this connection it is possible that understanding the abundance of Orthoptera populations in a pasture may provide some insight as to whether or not the pasture could provide a successful breeding habitat for these birds if mowing and grazing practices were carefully monitored.

Other adult birds are heavily reliant on Orthoptera as well, but not for themselves.  There are multiple bird species that depend almost solely on Orthoptera for their young during the rearing phase.  The fact that singing insects are relatively large and frequently abundant means they are a nutritionally valuable, easily located food item for parents to feed to their young.

Birds are not the only organisms that rely on Orthoptera for food.  Some predatory insects and spiders, as well as parasitic insects, depend on crickets, katydids, and grasshoppers.  Certain species of beetle larvae feed solely on grasshopper eggs, so their populations are directly reliant on grasshopper populations.  There are even some flies that parasitize crickets, katydids, and grasshoppers.  One interesting fact about all of this: a lot of these organisms that depend so heavily on Orthoptera actually use the sounds they produce in order to locate and predate them.

It is because so many other animals rely on Orthoptera that monitoring their populations provides some insight into the overall biodiversity of our landscapes.  Organisms that depend on Orthoptera will not thrive in these areas if the Orthoptera themselves are not flourishing.

Sound maps provide a relatively non-invasive way to create Orthoptera biodiversity estimates through landscapes, and may even provide insight into relative abundances of these populations.  They also provide a creative way to present and discuss scientific topics that may engage the public more than a traditional scientific study would.

If you want to learn more about the sound mapping projects we have done, including Orthopteran habitat maps from Hudson Valley orchards, visit https://hvfarmscape.org/sound-maps.

 

Additional Resources:

To learn insect song identifications for yourself, visit http://songsofinsects.com/.

To identify any species of cricket or katydid within North America, visit http://entomology.ifas.ufl.edu/walker/buzz/.

 

Helpful Singing Insect Guidebooks:

Capinera, J.L., Scott, R.D., and T.J. Walker.  2004.  Field Guide to Grasshoppers, Katydids, and Crickets of the United States.  Cornell University Press, Ithaca, New York.

Elliott, L. and W. Hershberger.  2006.  The Songs of Insects.  Houghton Mifflin Company, New York.

Himmelman, J. and M. DiGiorgio.  2009.  Guide to Night-singing Insects of the Northeast.  Stackpole Books, Mechanicsburg, Pennsylvania.

 

Works Consulted:

Capinera, J.L., Scott, R.D., and T.J. Walker.  2004.  Field Guide to Grasshoppers, Katydids, and Crickets of the United States.  Cornell University Press, Ithaca, New York.

Diwakar, S., Jain, M., and R. Balakrishnan.  2007.  Psychoacoustic sampling as a reliable, non-invasive method to monitor orthopteran species diversity in tropical forests.  Biodivers Conserv 16: 4081-4093.

Elliott, L. and W. Hershberger.  2006.  The Songs of Insects.  Houghton Mifflin Company, New York.

Gawałek, M., Dudek, K., Ekner-Grzyb, A., Kwieciński, Z., and J.H. Sliwowska.  2014.  Ecology of the field cricket (Gryllidae: Orthoptera) in farmland: the importance of livestock grazing.  North-Western Journal of Zoology 10(2): 325-332.

Humbert, J., Ghazoul, J., Richner, N. and T. Walter.  2010.  Hay harvesting causes high orthopteran mortality.  Agriculture, Ecosystems and Environment 139: 522-527.

Marini, L., Fontana, P., Battisti, A. and K.J. Gaston.  2009.  Agricultural management, vegetation traits and landscape drive orthopteran and butterfly diversity in a grassland-forest mosaic: a multi-scale approach.  Insect Conservation and Diversity 2: 213-220.

Marini, L., Bommarco, R. Fontana, P., and A. Battisti.  2010.  Disentangling effects of habitat diversity and area on orthopteran species with contrasting mobility.  Biological Conservation 143: 2164-2171.

 
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Posted by on December 23, 2019 in Uncategorized