Landscape Ecology of Singing Insects 3: Changes Over Time

by Carl Strang

Some of the formalism developed by landscape ecologists clarifies the current status of our singing insects and their prospects for survival. From the standpoint of a given species, the landscape is viewed as patches of habitat imbedded within a matrix of non-habitat. If that matrix is hostile to the species, the habitat edge is a “hard boundary,” and unless the species is good at dispersing long distances, they will be confined to their habitat island. To different degrees that extreme may not be met if there are steppingstones or corridors that can act as acceptable temporary refuges for dispersing individuals. I suspect that such is the case with pine tree crickets, for example. These habitat specialists are common in conifer groves across the region, many of which seem too isolated for such a small, specialized insect to cross the intervening distances. Nancy Collins, a Wisconsin specialist on the subfamily, has noticed that pine tree cricket nymphs can live, at least temporarily, in non-conifer, herbaceous habitats. Edges of conifer groves thus are not hard boundaries for pine tree crickets. In other cases, river corridors and highway rights-of-way can serve as travel lanes. Thus, the little-known dispersal abilities of our various species are key to understanding their status.

Pine tree cricket

In some of the crickets and katydids which normally are short-winged and flightless, long-winged morphs occasionally appear. Roesel’s katydid, mentioned in the previous post, essentially is never long-winged in its native Europe, but commonly is so here, where the species is expanding its range. There is a tradeoff in play for such species. Long-winged variants are good dispersers, but their fecundity is reduced.

Roesel’s katydid, long-winged variant

Dispersal also can be facilitated by humans. I have seen examples, with Japanese burrowing crickets and jumping bush crickets, of individuals and small groups showing up far ahead of the front of their range expansion, in places where landscape materials are stored or sold.

Mate finding motivates some movement by singing insects. The females in general must travel to meet up with singing males. The males themselves also may need to change their position. In DuPage County, where swamp cicadas are relatively few and scattered, I have observed males frequently changing position between songs by tens of meters at a time. An Iowa study (Shaw, Bitzer and North 1982) found that sword-bearing coneheads shifted position an average of 6.2m between nights, but otherwise remained associated with their group of other males.

Swamp cicada

The singing insects whose habitat needs are met by landscape alterations for agriculture and residential areas are the abundant, widespread ones. They are easily picked out by the large number of sites marked on their maps in my singing insects guide. Dispersal is relatively easy for them as there are large habitat blocks well connected by amenable corridors. Even they can suffer local extinction as land is cleared of vegetation for buildings or roadways. As new vegetation grows into such places, the weedy species are quick to re-establish themselves, but this underlines the dynamism of the habitat patch mosaic.

Of greater interest, and greater concern, are those species whose needs are not met by human-created habitats. Here the habitat patches are only a small percentage of the landscape, and elements of patch size, patch isolation, and insect dispersal ability become critical to understanding. Theory suggests that when a habitat falls below 10-20% of the landscape, dispersal ability is expected to drop dramatically in the absence of viable corridors or steppingstones; such is certainly the case for many of our habitat specialists. A few species anecdotally are good dispersers. I have reports, or have seen myself, instances of slender meadow katydids and long-tailed meadow katydids showing up in locations remote from their respective habitats. These individuals were unusual among the small meadow katydids in being long-winged morphs; most cannot fly.

Slender meadow katydid

Patch isolation in some cases is such that successful dispersal is impossible. Distances among the few surviving sphagnum bogs, for example, are too great to be crossed by sphagnum ground crickets. Prairie cicadas can fly, but apparently are disinclined to do so far enough to matter. At one of their sites, the West Chicago Prairie in DuPage County, they remain confined to one area of mixed grasses and forbs. They have not crossed the 350 meters of grasses, small shrubs and wetlands that separate them from a similar area within the same preserve. So far, their populations have persisted in remnant prairies ranging from 1 to a few acres. Can such small populations survive long term?

Prairie cicada

That question raises another concept from landscape ecology: extinction debt. This is the idea that a species’ habitat may have been so reduced that it still may be present but is doomed to fade away to extinction because its numbers are inadequate to maintain reproductive viability. Such may or may not be the case for prairie cicadas. I suspect this is what happened to northern wood crickets (NWC) in the region. NWC were known from two forested areas in northern Indiana at the beginning of the 20th Century (Blatchley 1903). One of these was in Marshall County. Years ago I used the original survey notes and county soil map to reconstruct the presettlement landscape of the township in question.

Presettlement map of Union Township, Marshall County, Indiana. Mesic forest was the large green area east of Lake Maxinkuckee.

Blatchley found NWC in the area of mesic forest which, in 1834, was very large. By the end of the 19th century agricultural clearing would have been well under way, and today only a tiny portion of that forest remains, the rest having been converted to pasture and crops. The same is true of forested areas in Lake County, Indiana, the other area where NWC lived in the late 1800’s. Though fragments of the forests where Blatchley found NWC remain, the crickets are gone, and I have checked all the other relatively large forests in the region without finding them. This raises the disturbing question: how many other species presently in the Chicago region are in a state of extinction debt? Patch size needed to maintain a species is dependent upon the characteristics of the species, its population dynamics, and patch quality. These are unknowns for all the uncommon species.

Our two species are Linnaeus’s 17-year cicada, on the left, and Cassin’s 17-year cicada, on the right

I will close this section with a case study on the periodical cicadas in DuPage County. In pre-settlement times the county was, from the cicadas’ perspective, a matrix of prairies and wetlands with 18 forested areas of various sizes scattered throughout. Historical maps and aerial photos allowed me to trace changes in those forests from the early 19th Century to the present day. I measured the forest sizes, noting their smallest (bottleneck) extents and how those were reflected in the presence of periodical cicada choruses in the 2007 emergence. There was a clear threshold of local extinction: forests which had remained above 61ha (hectares) still had cicadas, those which had fallen below 52ha did not, even when they had grown larger subsequently. Old newspaper accounts placed cicadas in at least some of these. Three forests which fell between those sizes appeared to have been affected by isolation, a remote one lacking cicadas, and two near persisting populations having them. The human history peculiar to the county is important here. DuPage County is immediately west of Chicago. The western half of the county quickly became agricultural, with forests cut back to make room for fields and pastures. Forests lacking cicadas in 2007 were mainly in the west. The eastern half developed residential commuter communities, with forests being protected and expanded as people planted trees around their homes. The largest area with cicada choruses in 2007 was lobular in shape, the various lobes following the routes of commuter-serving railways and the towns that expanded along them, connecting several of the pre-settlement forest locations. When the cicada choruses reached their peak in the first half of June, numbers of the insects suddenly appeared in flight, crossing over highways and other hostile environments. Subsequently, small groups showed up in places remote from the concentration areas. Whether these will result in significant expansion of the species in the county remains to be seen, but this observation supports the notion that competition and population pressure produce responses by the cicadas. They have the advantages of stronger flight capabilities and better vision than other singing insect groups.

One Last Look Back

by Carl Strang

My recent blog posts have shared highlights of this year’s field season, as I searched for singing insects in the 22-county area I define as the Chicago region. Those accounts haven’t told the whole story, though, and I have a few last photos to shake out of the bag. These fill out some of the experience of doing this kind of regional study.

For instance, other animals have enhanced the delight.

The chalk-fronted corporal is a dragonfly I have encountered only in the northern portion of the region, in this case at the Lulu Lake Nature Preserve in northern Walworth County, Wisconsin.

Walsh’s grasshopper was a new one for me. Not a singing species, but an interesting find at the Poverty Prairie in DuPage County’s Waterfall Glen Forest Preserve.

Turkey vultures assemble at dusk on the Culver, Indiana, water tower. My travels take me back to my home town a few times each season.

Interesting and beautiful scenes are to be found in the relatively undisturbed wild areas which are my main destinations.

An early evening rainbow at Conrad Station in the Indiana Kankakee Sands presaged a thunderstorm-dodging drive home on July 2.

Pinholes between tree leaves cast solar eclipse shadows at Blackwell Forest Preserve. Though the moon covered around 90% of the sun at peak, I detected no change in singing insect activity.

One of the more beautiful scenes was this panne in the Indiana dunes.

I had hoped to find delicate meadow katydids in the pannes. Dusky-faced meadow katydids were a good find there, but that species has a solid hold in other dunes wetlands.

The Pembroke Savanna in the Illinois Kankakee Sands is one of my favorite sites.

I believe these white pines at Warren Dunes State Park in Berrien County, Michigan, are the same ones where Richard Alexander found treetop bush katydids in 1971. He described the trees as small, but all are tall now. They still foster pine tree crickets, but I did not find any bush katydids.

I ended up with 115 county records for the season, totaling all newly found singing insect species over all the counties.

So far, I have found sprinkled grasshoppers only in oak savannas on sand soils.

Dusky-faced meadow katydids at the Indiana Kankakee Sands were a Newton County record.

This curve-tailed bush katydid at the Jasper-Pulaski Fish and Wildlife Area in Indiana provided a Jasper County record for my study.

I found a healthy population of long-tailed meadow katydids, including this brown-legged male, at Ferson Creek Fen in Kane County.

The Ferson Creek population also had green-legged variants, including this female.

Lisa Rainsong, Wendy Partridge and I drove south to Loda Prairie to check out the bush cicadas there. I concluded this year that the species does not occur in the Chicago region.

This Texas bush katydid was singing in early October at Springbrook Prairie Forest Preserve, DuPage County. I had an observation of this species on October 17, my latest ever in the region.

Most of the long winter remains, and as I compile data, write reports, and visit museums, I will be looking forward to another collection of rich experiences as I resume my field study in 2018.

 

Christmas, North Carolina

by Carl Strang

My brother Gary and his wife Lisa have moved from the Eastern Shore of Maryland down to coastal North Carolina, and I joined them there for the week around Christmas. Most of our time went into unpacking and some yard work, but there were plenty of moments to explore the surroundings.

One corner of their property extends into a swamp complete with bald cypress “knees.”

One corner of their property extends into a swamp complete with bald cypress “knees.”

Some of the trees also have the iconic southern epiphyte, Spanish moss.

The most charming critter award went to the anoles that climbed the walls, shrubs and yard furniture.

It’s easy to project lots of personality into these little lizards.

It’s easy to project lots of personality into these little lizards.

Most were wearing their basic brown.

Most were wearing their basic brown.

A few switched to green, demonstrating why some call them “chameleons.”

A few switched to green, demonstrating why some call them “chameleons.”

There still were several species of singing insects performing in the unseasonably warm temperatures of those days. I recognized Carolina ground crickets, southern ground crickets (song identical to that of the striped ground cricket of the North), pine tree crickets, and abundant jumping bush crickets. I was left with a mystery, two individuals of a fifth species that sang from lawns after dark. Here is a recording:

Most of the time the spacing between trills was more evenly rhythmic than in this recording.

The recording was made well out in the lawn in front of Gary’s house.

The recording was made well out in the lawn in front of Gary’s house.

I was able to locate the presumed cricket’s position within a few square inches, but unsuccessful in seeing him. He must have been well concealed in a soil crack or tunnel. At first I thought, from the sound and the habitat, that he must be a ground cricket, but his song was louder than most ground crickets and I have never encountered a ground cricket that sings only after dark. A quick review of ground cricket recordings, and those of other likely cricket groups, in the Singing Insects of North America website, failed to turn up a match. If anyone recognizes this, I would appreciate the tip, but it was great to leave North Carolina with a mystery in hand.

 

Lessons from a Tiny Teacher

by Carl Strang

A moment came Saturday night when I had an experience which seldom happens anymore. I was walking to my car to head home from Mayslake Forest Preserve after watching First Folio Theater’s excellent performance of Shakespeare’s The Merry Wives of Windsor on the outdoor stage. I heard a singing insect that I did not recognize.

This was at the end of a day that had been fairly productive. I had found green-winged cicadas in two additional counties in the afternoon. During the play’s intermission I heard the first sword-bearing coneheads of the year in Mayslake’s prairies. I also heard the first unambiguous fall field crickets of the season.

But then, as I headed for the car, I heard a trill that seemed unfamiliar. At first I thought it was probably something I was hearing for the first time this season, and its identity would click if I just listened for a short time. While waiting for that click to happen I went through the mental checklist. It was a high-pitched, musical trill. So, it had to be a cricket. I approached it, and the hidden insect kept singing until I was beneath it. So, it had to be a tree cricket. I looked up into the spruce above me, but without a flashlight there wasn’t even a small possibility of seeing it. The checklist continued. All the early arboreal tree crickets have pauses in their trills, at least little ones. Therefore it wasn’t a two-spotted, or a Davis’s, and certainly not a snowy. I knew I would be there at night in a little over a week, and resolved to make a recording then. It wasn’t until later that the obvious solution filtered through the late night fatigue. It had to be a pine tree cricket. I realized that I had allowed myself to think of Oecanthus pini as a late-season species, but that was because Nancy Collins introduced me to pine tree crickets in September last year. I had noted that they were going strong at that point, and so could not say when they had begun. Everything fit. It was a continuous musical trill, but not as loud as tree crickets usually are. It was in a conifer. The Singing Insects of North America website gives starting dates consistent with the end of July at this latitude.

Pine tree cricket

Pine tree cricket

The lessons were several: be open to all sounds, notice them all; pursue incongruities if a song isn’t a clear match with past experience; abandon assumptions that are constructed from limited past experience. That’s a lot of profit gained from one tiny cricket, and I am grateful.

Sound Ideas: Trilling Tree Crickets

by Carl Strang

Today I wish to share recordings of 4 species of our tree crickets, which have in common songs that are continuous (rather than interrupted) trills. I will order them along a typical habitat gradient, from grasses to mixed grasses and forbs to mixed forbs and shrubs to trees (specifically, conifers).

The four-spotted tree cricket seems to prefer to sing from grass stems.

Four-spotted tree crickets are pale.

Four-spotted tree crickets are pale.

The song is a continuous clear trill:

Very abundant late in the season, Forbes’s tree cricket prefers forbs or vines.

Forbes’s tree cricket is highly variable, but usually has some dark markings.

Forbes’s tree cricket is highly variable, but usually has some dark markings.

Here is a recording from last year:

There is an interesting issue surrounding these first two songs, in my mind. I know of other singing insect students who, like me, at least sometimes can distinguish the songs of four-spotted and Forbes’s tree crickets, but we describe them with different language. To me, the four-spotted’s song has more of a clear, tone-like quality, while the Forbes’s song has a discordant tone that others apparently don’t hear. Others point to the difference in pulse rate (much faster in Forbes’s, but I need a computer analysis of a recording to tell that difference). This is the best example I have found of how describing insect songs in words can be difficult, and may in some cases be impossible.

Woodland shrubby understories to masses of forbs in open places near wooded edges are habitat for our third species, the broad-winged tree cricket. Here is its song:

Broad-winged tree crickets are distinguished by the wide wings and the raspberry coloration on the head and antenna bases.

Broad-winged tree crickets are distinguished by the wide wings and the raspberry coloration on the head and antenna bases.

To my ear, this song has a richer tone, and usually is lower in pitch than other trilling tree crickets at the same temperature.

I’ll close with the pine tree cricket, perhaps the most beautiful of the four.

The red-browns and pale greens provide good camouflage in a habitat of coniferous trees.

The red-browns and pale greens provide good camouflage in a habitat of coniferous trees.

The following recording was made indoors, from a caged male (you can hear the splashing of the aquarium pump in the background):

Again the trill is continuous and similar to the others, especially the four-spotted tree cricket, but the source of the sound in a pine, spruce or cedar (usually in a grove of them) is a dead give-away.

Mayslake Update

by Carl Strang

Today, some accumulated photos from, or at least connected to, Mayslake Forest Preserve.

The stream corridor marsh has become dry for the second year in a row, though this time it happened a couple months later.

The stream corridor marsh has become dry for the second year in a row, though this time it happened a couple months later.

Insects provided some photo ops.

This female sword-bearing conehead was the first of its kind I have seen at Mayslake in three years.

This female sword-bearing conehead was the first of its kind I have seen at Mayslake in three years.

Scissor-grinder cicadas occur in greater densities at Mayslake than in any other place I have found them to date.

Scissor-grinder cicadas occur in greater densities at Mayslake than in any other place I have found them to date.

This short-winged grasshopper appears to be a Melanoplus borealis, but I am not entirely sure.

This short-winged grasshopper appears to be a Melanoplus borealis, but I am not entirely sure.

The backdrop for the final photo is from Mayslake, but the pine tree cricket is the one Nancy Collins sent me from Wisconsin, still singing weeks later.

The cricket’s camouflage is superb.

The cricket’s camouflage is superb.

Snow fell for the first time yesterday: time for a new seasonal transition.

Pine Tree Cricket

by Carl Strang

One of the nicest aspects of scientific inquiry is the discovery of other people pursuing shared interests. My own study of singing insects in northeast Illinois, northwest Indiana and adjacent counties in Wisconsin and Indiana has placed me in contact with Gideon Ney, whose pursuit of coneheaded katydid evolution in his Ph.D. thesis work at the University of Missouri has added the marsh conehead and slightly musical conehead to the region’s species list. Dennis Nyberg and associates at the University of Illinois Chicago have led me to the short-grass prairie cicada. Botanist Scott Namestnik and I have collaborated in mapping the regional distribution of Roesel’s katydids.  Lisa Rainsong conducts a similar regional survey of species in the Cleveland area, allowing a valuable comparison of notes. And now I owe my thanks to Nancy Collins for introducing me to the pine tree cricket. Nancy is one of those rare people who develop such a strong interest in some aspect of natural history that they go on to make genuine contributions to science. She has traveled through the U.S. and into Central America searching for tree crickets, and has been involved in the discovery of new species. Her website provides an excellent overview of this charming group of insects.

Nancy came out to the Bong Recreation Area when I was surveying the southeast Wisconsin counties a couple of weeks ago, and helped me learn to recognize the song of the pine tree cricket. She also provided a male for me to photograph and record in an isolated indoor setting.

Pine tree cricket, recovering from a few minutes in the freezer to slow him down so I could photograph him.

Pine tree cricket, recovering from a few minutes in the freezer to slow him down so I could photograph him.

And the ventral view. At some point I will risk a more lifelike pose with him warmer and more active.

And the ventral view. At some point I will risk a more lifelike pose with him warmer and more active.

I had not focused on this species because the references seemed to indicate that it is only on the fringe of my area. Thanks to Nancy I now expect to find pine tree crickets throughout the survey area. Already I have found two populations in DuPage County, for instance, one of them at Mayslake where I work, and the other two miles from my home, at Fermilab. The Fermi population is particularly instructive, because the groves of conifers hosting the crickets are widely separated by expanses of prairie. This is a small insect with a narrowly defined habitat, but impressive dispersal ability. I suspect they have been able to jump around mainly by their affinity for red cedars, which readily spring up in open areas where birds disperse their seeds after eating the berry-like cones.

The song is not particularly intrusive, but easily recognized if you know what to listen for. Approach a large grove of coniferous trees in late summer or early autumn, late afternoon or early evening, and listen for a steady, high-pitched, sweet-toned trill. No other singing insect in the region has this peculiar attachment to conifers. The song of a single cricket is not particularly loud, but a chorus of them adds up significantly, and I had no trouble hearing those at Fermilab as I passed the spruces and cedars on my bicycle. Interestingly, and somewhat ironically, there were fewer in the pine groves.

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