Dancing Flies

by Carl Strang

A program had me at Kline Creek Farm early one morning last week. While waiting at the parking lot for others to arrive, I noticed a swarm of small flies engaged in what I took to be a courtship dance. They were in the light at the edge of a tree-cast shadow, and they remained in the vertical plane defined by that edge, within an altitude range of about 5-8 feet, the zone parallel to the ground and around 20 feet long. Each fly followed a roller-coaster or sine-wave flight path, turning around when it reached each end of the zone.  They were going too fast to follow easily, and I had no net with me. I took a few photos.

The flies could be seen clearly only when backlit. Each bright dot is a different fly.

The flies could be seen clearly only when backlit. Each bright dot is a different fly.

The flies in focus in each photo had similar shapes. Here are two examples:

There is a large spot in the middle, and two lines at each side. The shutter speed is 1/1000 second.

There is a large spot in the middle, and two lines at each side. The shutter speed is 1/1000 second.

Often there were additional projections above and below.

Often there were additional projections above and below.

There is a family of flies called dance flies, the Empididae. They are famous in ethological circles for the nuptial gifts offered by males to females. In some species the pattern is regarded as more primitive, and the gift is a prey item. In others the male wraps the prey in silk. At the other end of the spectrum are species in which the male creates a balloon of silk, and this has replaced the prey entirely. Were the photographed flies members of this family? I do not know. Empidids have bulbous thoraxes, which would account for the bright central spot in the photos. The abdomen is thin, and the long central line could be a highlight, with the wings similarly indicated by the lines to each side. The thicker line below could be the dangling long legs, or perhaps the long proboscis that some species of empidids possess, if these were in fact empidids. Whatever they were, they were fascinating to watch. The shadow-edge convention provides a standardized meeting site, reminiscent of hilltopping butterflies. I found the up-and-down motion of the individual flies hypnotic, the experience delightful.

Spring Bird Count

by Carl Strang

Saturday was the Spring Bird Count in DuPage County. I explained the principle in my description of last December’s Christmas Count . I have less to show you on the spring count. The area was much the same, and again was led by Urs Geiser. There were enough of us to split into two subgroups. I was joined in my subgroup by Michael Marlow and Bruce Struckman. We covered Kline Creek Farm and the nearby North Woods subdivision, a beautifully wooded area surrounded on all sides by forest preserves. The only bird photo I managed to get was of our first scarlet tanager.

Scarlet tanager b

Other highlights were a vesper sparrow, a bald eagle, and three golden-winged warblers, plus a variety of other beautiful birds briefly glimpsed or heard through the dense vegetation in the gusting winds that impaired us that day.

CBC Part 2

By Carl Strang


Yesterday I outlined the story of a shared day with other birders in the Christmas Bird Count. Today I am finishing with some of the birds we were especially happy to find, species we certainly don’t see every winter day.


One of these species was the purple finch. We saw both males




and female-plumaged individuals, some of which may have been first-year males.




The single most unusual bird of the day was this rusty blackbird.




Its head showed the sharply contrasting rusty tones of winter plumage that give the species its name, but this male appeared to be delayed in its body feather molt.




A final species of special interest was the eastern bluebird. We saw two small groups of them, one along the Prairie Path containing this female.




The second group was at Kline Creek Farm, and included this hackberry-loving male.



CBC Part 1

by Carl Strang


Yesterday was the Fermilab Christmas Bird Count, in which I have participated for several years now. It’s an opportunity for birders to join in a continent-wide effort to compile an annual snapshot of bird numbers and geography. Other groups cover other areas at other times, generally in the second half of December or early in January.


Each count circle is divided into areas, 8 in the circle centered on the Fermilab grounds. Here are the other members of our Area 4 group from yesterday, left to right in the photo: Judy Morgan, Linda and Frank Padera, Chuck Drake, Marcia and Lee Nye, and group leader Urs Geiser.




Our day began very early, with most of the morning devoted to covering a 4-mile stretch of Prairie Path northwest from the intersection of County Farm and Geneva Roads. If the birds were competing to be counted, on this day the starlings jumped to an early lead with this tightly packed mob on the wire, and never looked back.




As you might expect, most of the birds we see are of the more common or familiar species, like this white-breasted nuthatch.




The icy snowfall of a couple days ago made walking more of an effort than in many years, but did add to the beauty of the scenery.




While birds that were moving and calling were easy to find, others held still and required a little more effort, like this mourning dove.




We encountered great horned owl tracks in the snow.




The night before, the owl had killed a cottontail rabbit.




Tracks don’t count, however, so we could not include the owl on the day’s list. We also saw a coyote, and passed where it or another had caught a mouse or vole beside the trail.




The day’s tally included several red-bellied woodpeckers,




as well as downy woodpeckers.




In the afternoon we explored additional sites, such as Kline Creek Farm (cattle also don’t make the list, nor did we find any cowbirds).




Tomorrow I’ll share some of the birds that were unusual enough to get us especially excited.

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