David Krooshof

Dark Trails

When taking a photo with a long shuttertime, all bright parts that move relative to the camera, draw a trail. Pete Mauney is a master at making photos in which fireflies, airplanes, traffic and stars all draw their light trails through his images. I've been a fan for years.

There are no fireflies where I live. But there is another interesting family of animals, one that nearly invisible navigates around us: Bats. When I studied biology (1 year) we went into the fields and a teacher pointed them out to me. I noticed I was able to hear their communications (not their sonar). Spotting bats while biking around at dusk, became a sport for a while.

Above the canals of Amsterdam, countless bats feast on the mosquitos, eating thousands of them every night. I was decades older when I moved to Amsterdam I so I was no longer able to hear the bats. In 2011, I made a bat detector out of a kit. That's a device that translates the sonar of the bats from ±40.000 Hz down to ±1.000 Hz, making the sonar very audible for older humans.

You can hear them closing in on their prey, their sonar getting faster and faster:

"Tee tee tee tee t t tttttrrrrrrt!"

I always thought bats flew erratically. But through the bat detector I learned this is not true. They fly in gorgeous curves. I wanted to record this. I wanted to make curves they fly visible. Pete advised me that shooting video is the way to go. I got to work to try and pull this off.

Two bats

The process

A composite of several exposures shot in succession, is called a chronophotograph.

The method is to shoot video, then load a few seconds of it into photoshop. There, I stack the video frames on top of each other. The algorithm is this: Pixel by pixel, each frame is checked. The darkest variant of that pixel gets to be in the output layer. Then the next pixel is evaluated in the same way. My old laptop takes a long time to process this, especially if use all 500 layers photoshop allows me to use at once.

In general, I keep a few backgroud frames, that use a different method on. Here, I take a mean of these frames. This reduces the noise. I got this trick from the astrophotographers. Most images shot at dusk, are a hybrid between these two process.

To the left, an apartment buiding. The bottom of the frame is the roof of a school. At the top of the frame runs a rainbow. I heard a crow approaching, and started the video. The curve that the crow flies, compliments the rainbow.

I took a picture of this rainbow, when I heard a crow approaching, and started the video. This is one of the first trails managed to process well.

I first used my photo cameras to shoot the videos. But they only shoot in "full HD". And then I realized that I have one camera that can do 4K video: My phone. Not before long, these images led to an exhibition in the US, where my Dark Trials were presented accross the room from Pete Mauneys Light Trails. It was Stephen DiRado who invited is both. I'm very proud and I had the best of times there.

So here I am, shooting these huge analog cameras, and the camera that got me to go accross the ocean, was my phone. To be fair, my phone is my most expensive camera.

  • Black and white image. To the left there is a tree. Three black birds fly up from the bottom of the frame. There is a forth one, faintly in the back ground. A half moon stands out brightly.
  • Black and deeply blue image, shot just after dusk. The flock arrives at the apartment buildings from afar, and navigates in an S curve between the two buildings. Some windows reflect what is left of the sunset, in green. The focus is unusual, as the plane lies nearly parallel to the flight pattern. There is a dreamy atmosphere to this image.
  • Dusk. The sky is blue at the top, but orange at the horizon. The horizon shows many silhouettes of trees in the far background. There is a double stemmed tree in the front. The crows left the tree in two groups. One flew to the right immediately, the other flew a circle first. In the image, the crows flying straight have exited the frame, while the circling crows have only just completed one turn.

Bats and birds

While figuring out how to record bats, the local jackdaws kept flying through the frame, and they became my test pilots.

I went out shooting video every night at dusk. The trick to get usable footage, is to walk around with the camera mounted on a tripod, while it is recording. I can compose real fast, but if I were to hit record as soon as the camera was set up, the seconds the camera takes to start recording would make me miss the fly over time and again.

When I heard crows, jackdaws (a smallish corvid) or bats, I quickly composed the view, anticipating the animals to fly through the frame.

Overlooking the pond of the old parliament building. The sky has a dark trail process, the building and the water have a light trail process. The birds in the sky are black, above the water, they are white. Some trails are double. Those were pairs of jackdaws.

Chronophotograph of various birds flying near the Dutch parliament building

Jackdaws are stinky, but really nice. Within the flock, they fly in pairs. In the daytime, they spread out, but at dusk, they gather in the trees in the village where I live now. The offspring keep begging for food with their parents until they are so old I can not tell them apart from the older birds.

I also noticed that they beg for food from crows. The crows are able to pull worms from the ground, that the jackdaws can't. The crows live in much smaller groups, nuclear families, but they like the company of the many jackdaws. There are often a few crows flying along with the flock of jackdaws. The crows can be recognized in the Dark Trails, because they, contrary to the saying in English, do not fly as straight as the jackdaws do.

Also, jackdaws "kiss" in mid air. If you see double trails in my image, you can bet it is a pair of jackdaws. They should become an icon for love.


While processing a bit of video of seaguls, Ryan walked in, and backwards out of the frame. I decided to keep her in the image. From this point on, I included humans in the frame, pushing the birds to the background. This also led to many self portraits. Easy to do, the camera is on a tripod anyway.

Once I biked under a tree with thousands of starlings. I got shat on.

  • Ryan at the beach. A low wave is just coming in. She walks backwards, this is no trail, just a still. The very low stand point make the shells in the sand big. Dark trails of seaguls and of a kit make this image remarkable. One trail on the right side compliments the foam on the incoming wave.
  • Shot from a very low vantage point, only centimeters above the sand, overlooking the sea. Over a dozen starfish with an “old pink” color, sit on a big rounded block of wood. A foamy wave is coming in, and has just hit the back of the block. Meanwhile, a kitesurfer is passing behind this scene. He leaves a colourful light blue trail. There is also a trail of a seagull, but it is spaced further apart than other trails of birds, because the frame rate is kept low, because that looked better for the surfer.
  • Some green trees near a pond. The sun is setting behind them. Me and my dog are silhouettes under a willow tree, in the setting sun. Only in the top of the frame, there are dark trails of crows. With the light shining through their feathers, they look orange. Who knew? A jackdaw behind them is still grey looking.
  • At the backside of the palace, a lot is going on. There is a big black door, and on each side windows with iron cross bars. A 5 layer stone staircase leads up to the door. On the left, 4 tourists are having lunch, each sitting on a different level. The lowest one bends over, the second one a bit, the third sits more or less straight and notices me filming. The forth is a woman. She looks at the other three guys. On the right side is a red scooter, with two young guys on them. 
In the middle is an old man. He wears a crown. He is feeding the doves that sit on his lap.
There is a dark trail of the shadow that dove threw onto the palace, while landing to be fed by the old man.
  • A water filled ditch, reflecting the sky, and a gravel road go straight into one point in the middle of the horizon. The camera is pointing up a bit. Trees to the left are dark, but the trees to the right of the road bathe in orange light of a sunset. Starlings approach these trees. Some dive right into it, others decide to do a go-around first.
Since the camera was on a tripod, I was free to bike into the frame. When I was under the trees, I got shat on.

Composites of Dark trails with birds and stills of people. Each of thee were made out of a few seconds of 4K video and nothing else. The humans were simply one frame out of the video, exept the kite surfer.


  • Curves of 5 bats flying between some trees. The sun has just set. The background is a gradient from a purplish blue to a deep red. On the left side, at the horizon, you can see clouds above the apartment buildings. This is the jackdaw flock, literally pushed into the background.

This what I wanted all along. Dark trails of bats. Mission accomplished. It took me a year to pull this off, but I managed.

Worcester, MA

I'm so thankful that Clark University invited me to be a part of their exhibition. It was an honor and a crown on my work. I got to give a talk, a lecture, discuss the work of students, and to meet so many great people I previously only knew through facebook. It was such a magical time!

  • Poster saying...
  • Seth David Rubin, Stephen DiRado, Pete Mauney, David Krooshof in the exhibition. To the left, four of my images, carefully printed by Clark students, hung from the wall with magnets. There were 15 of these in the show.
  • David Krooshof in a red suit talking about grabbing images. Photo by Frank Armstrong.
  • Several big printers in a windowless room. No less than 4 copies of the photo of the woman between the seagulls are scattered around the room.
  • Frank Armstrong an Stephen DiRado, teaching in their cosy classroom. Stephen is seen from the back. He is so engaged with the class, that he’s partly over the table. Students listen closely. Colourful Christmas lights dangle from the ceiling.
  • Wide angle shot of a man with a long white beard and longish hair. It's Pete Mauney. He has a very deep voice. He reaches for his food, exaggerated with by the wide angle lens. In the back, in red sits another man, with black hair.  That's Matt Malsky.
  • I was fascinated by the rusty railway bridges. Stephen and I were riding in his wife Donna's cabrio, with the top down. This is a wide angle shot taken from the stick shift, looking up at us and two of the bridges. 
The wide angle lens distorted our head shapes. We both look over at the street, but due to -again- the wide angle view, this seems to be in different positions.

The jackdaws were never really the goal, though I have been pre-occupied with their chatter for decades. I was friends with a small group of them when I lived in Scheveningen from 1996 to 2005, after I saved one of them from a cat. They liked to sit in the tree in front of my house especially if I was on the balcony. Their waves of vocalisations inspired me to use the boids algorithm in my music to have a flock of guitar notes from each single plucking of a string.

After I nailed that red bats photo, I had calm down from listening out for the jackdaws. Not from the dark trails series, but from these birds specifically. It had became a fixation to scan the audible field for the local flock. I had done so for a year, to be able to set up the composition in the camera quickly enough. I could hear where they were from miles away, and I could tell if they'd come near or not, and it alerted me instantly. I had to give it a rest. It took me over a month or so before I could shake it off.

I still have a metric tonne of footage that can be converted into trails. I have processed some of these since. I have been talking with a programmer to make an app for this process. I think I will revisit it then. In the past year and a half, my process went from fully manual, punching holes in layers, to largely automatic. This was not a time saver, though. The time I saved was put to use to make better selections in the video, better choices in frame rate, better handling of the noise, but not in more hours of sleep.

Looking back, I think there is poetry in the red bat photo in the sense that the jackdaws and the odd apartment buildings are still there, but in the background. If you listen to the footage, you can hear me saying the above statements to Ryan.

I nailed the ultimate goal of this project, just before I went to the USA with this work. I'm very proud of what I had accoplished and that is was recieved so well, too.

Two photos have been published in magazines: One in the Juniper Rag, and one in a Dutch photo magazine, with a nice explanation by Eduard de Kam.